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| <book> |
| <?dbhtml filename="index.html"> |
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| <!-- ****************************************************** --> |
| <!-- Header --> |
| <!-- ****************************************************** --> |
| <bookinfo> |
| <title>Writing an ALSA Driver</title> |
| <author> |
| <firstname>Takashi</firstname> |
| <surname>Iwai</surname> |
| <affiliation> |
| <address> |
| <email>tiwai@suse.de</email> |
| </address> |
| </affiliation> |
| </author> |
| |
| <date>October 6, 2005</date> |
| <edition>0.3.5</edition> |
| |
| <abstract> |
| <para> |
| This document describes how to write an ALSA (Advanced Linux |
| Sound Architecture) driver. |
| </para> |
| </abstract> |
| |
| <legalnotice> |
| <para> |
| Copyright (c) 2002-2005 Takashi Iwai <email>tiwai@suse.de</email> |
| </para> |
| |
| <para> |
| This document is free; you can redistribute it and/or modify it |
| under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2 of the License, or |
| (at your option) any later version. |
| </para> |
| |
| <para> |
| This document is distributed in the hope that it will be useful, |
| but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the |
| implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A |
| PARTICULAR PURPOSE</emphasis>. See the GNU General Public License |
| for more details. |
| </para> |
| |
| <para> |
| You should have received a copy of the GNU General Public |
| License along with this program; if not, write to the Free |
| Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, |
| MA 02111-1307 USA |
| </para> |
| </legalnotice> |
| |
| </bookinfo> |
| |
| <!-- ****************************************************** --> |
| <!-- Preface --> |
| <!-- ****************************************************** --> |
| <preface id="preface"> |
| <title>Preface</title> |
| <para> |
| This document describes how to write an |
| <ulink url="http://www.alsa-project.org/"><citetitle> |
| ALSA (Advanced Linux Sound Architecture)</citetitle></ulink> |
| driver. The document focuses mainly on the PCI soundcard. |
| In the case of other device types, the API might |
| be different, too. However, at least the ALSA kernel API is |
| consistent, and therefore it would be still a bit help for |
| writing them. |
| </para> |
| |
| <para> |
| The target of this document is ones who already have enough |
| skill of C language and have the basic knowledge of linux |
| kernel programming. This document doesn't explain the general |
| topics of linux kernel codes and doesn't cover the detail of |
| implementation of each low-level driver. It describes only how is |
| the standard way to write a PCI sound driver on ALSA. |
| </para> |
| |
| <para> |
| If you are already familiar with the older ALSA ver.0.5.x, you |
| can check the drivers such as <filename>es1938.c</filename> or |
| <filename>maestro3.c</filename> which have also almost the same |
| code-base in the ALSA 0.5.x tree, so you can compare the differences. |
| </para> |
| |
| <para> |
| This document is still a draft version. Any feedbacks and |
| corrections, please!! |
| </para> |
| </preface> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- File Tree Structure --> |
| <!-- ****************************************************** --> |
| <chapter id="file-tree"> |
| <title>File Tree Structure</title> |
| |
| <section id="file-tree-general"> |
| <title>General</title> |
| <para> |
| The ALSA drivers are provided in the two ways. |
| </para> |
| |
| <para> |
| One is the trees provided as a tarball or via cvs from the |
| ALSA's ftp site, and another is the 2.6 (or later) Linux kernel |
| tree. To synchronize both, the ALSA driver tree is split into |
| two different trees: alsa-kernel and alsa-driver. The former |
| contains purely the source codes for the Linux 2.6 (or later) |
| tree. This tree is designed only for compilation on 2.6 or |
| later environment. The latter, alsa-driver, contains many subtle |
| files for compiling the ALSA driver on the outside of Linux |
| kernel like configure script, the wrapper functions for older, |
| 2.2 and 2.4 kernels, to adapt the latest kernel API, |
| and additional drivers which are still in development or in |
| tests. The drivers in alsa-driver tree will be moved to |
| alsa-kernel (eventually 2.6 kernel tree) once when they are |
| finished and confirmed to work fine. |
| </para> |
| |
| <para> |
| The file tree structure of ALSA driver is depicted below. Both |
| alsa-kernel and alsa-driver have almost the same file |
| structure, except for <quote>core</quote> directory. It's |
| named as <quote>acore</quote> in alsa-driver tree. |
| |
| <example> |
| <title>ALSA File Tree Structure</title> |
| <literallayout> |
| sound |
| /core |
| /oss |
| /seq |
| /oss |
| /instr |
| /ioctl32 |
| /include |
| /drivers |
| /mpu401 |
| /opl3 |
| /i2c |
| /l3 |
| /synth |
| /emux |
| /pci |
| /(cards) |
| /isa |
| /(cards) |
| /arm |
| /ppc |
| /sparc |
| /usb |
| /pcmcia /(cards) |
| /oss |
| </literallayout> |
| </example> |
| </para> |
| </section> |
| |
| <section id="file-tree-core-directory"> |
| <title>core directory</title> |
| <para> |
| This directory contains the middle layer, that is, the heart |
| of ALSA drivers. In this directory, the native ALSA modules are |
| stored. The sub-directories contain different modules and are |
| dependent upon the kernel config. |
| </para> |
| |
| <section id="file-tree-core-directory-oss"> |
| <title>core/oss</title> |
| |
| <para> |
| The codes for PCM and mixer OSS emulation modules are stored |
| in this directory. The rawmidi OSS emulation is included in |
| the ALSA rawmidi code since it's quite small. The sequencer |
| code is stored in core/seq/oss directory (see |
| <link linkend="file-tree-core-directory-seq-oss"><citetitle> |
| below</citetitle></link>). |
| </para> |
| </section> |
| |
| <section id="file-tree-core-directory-ioctl32"> |
| <title>core/ioctl32</title> |
| |
| <para> |
| This directory contains the 32bit-ioctl wrappers for 64bit |
| architectures such like x86-64, ppc64 and sparc64. For 32bit |
| and alpha architectures, these are not compiled. |
| </para> |
| </section> |
| |
| <section id="file-tree-core-directory-seq"> |
| <title>core/seq</title> |
| <para> |
| This and its sub-directories are for the ALSA |
| sequencer. This directory contains the sequencer core and |
| primary sequencer modules such like snd-seq-midi, |
| snd-seq-virmidi, etc. They are compiled only when |
| <constant>CONFIG_SND_SEQUENCER</constant> is set in the kernel |
| config. |
| </para> |
| </section> |
| |
| <section id="file-tree-core-directory-seq-oss"> |
| <title>core/seq/oss</title> |
| <para> |
| This contains the OSS sequencer emulation codes. |
| </para> |
| </section> |
| |
| <section id="file-tree-core-directory-deq-instr"> |
| <title>core/seq/instr</title> |
| <para> |
| This directory contains the modules for the sequencer |
| instrument layer. |
| </para> |
| </section> |
| </section> |
| |
| <section id="file-tree-include-directory"> |
| <title>include directory</title> |
| <para> |
| This is the place for the public header files of ALSA drivers, |
| which are to be exported to the user-space, or included by |
| several files at different directories. Basically, the private |
| header files should not be placed in this directory, but you may |
| still find files there, due to historical reason :) |
| </para> |
| </section> |
| |
| <section id="file-tree-drivers-directory"> |
| <title>drivers directory</title> |
| <para> |
| This directory contains the codes shared among different drivers |
| on the different architectures. They are hence supposed not to be |
| architecture-specific. |
| For example, the dummy pcm driver and the serial MIDI |
| driver are found in this directory. In the sub-directories, |
| there are the codes for components which are independent from |
| bus and cpu architectures. |
| </para> |
| |
| <section id="file-tree-drivers-directory-mpu401"> |
| <title>drivers/mpu401</title> |
| <para> |
| The MPU401 and MPU401-UART modules are stored here. |
| </para> |
| </section> |
| |
| <section id="file-tree-drivers-directory-opl3"> |
| <title>drivers/opl3 and opl4</title> |
| <para> |
| The OPL3 and OPL4 FM-synth stuff is found here. |
| </para> |
| </section> |
| </section> |
| |
| <section id="file-tree-i2c-directory"> |
| <title>i2c directory</title> |
| <para> |
| This contains the ALSA i2c components. |
| </para> |
| |
| <para> |
| Although there is a standard i2c layer on Linux, ALSA has its |
| own i2c codes for some cards, because the soundcard needs only a |
| simple operation and the standard i2c API is too complicated for |
| such a purpose. |
| </para> |
| |
| <section id="file-tree-i2c-directory-l3"> |
| <title>i2c/l3</title> |
| <para> |
| This is a sub-directory for ARM L3 i2c. |
| </para> |
| </section> |
| </section> |
| |
| <section id="file-tree-synth-directory"> |
| <title>synth directory</title> |
| <para> |
| This contains the synth middle-level modules. |
| </para> |
| |
| <para> |
| So far, there is only Emu8000/Emu10k1 synth driver under |
| synth/emux sub-directory. |
| </para> |
| </section> |
| |
| <section id="file-tree-pci-directory"> |
| <title>pci directory</title> |
| <para> |
| This and its sub-directories hold the top-level card modules |
| for PCI soundcards and the codes specific to the PCI BUS. |
| </para> |
| |
| <para> |
| The drivers compiled from a single file is stored directly on |
| pci directory, while the drivers with several source files are |
| stored on its own sub-directory (e.g. emu10k1, ice1712). |
| </para> |
| </section> |
| |
| <section id="file-tree-isa-directory"> |
| <title>isa directory</title> |
| <para> |
| This and its sub-directories hold the top-level card modules |
| for ISA soundcards. |
| </para> |
| </section> |
| |
| <section id="file-tree-arm-ppc-sparc-directories"> |
| <title>arm, ppc, and sparc directories</title> |
| <para> |
| These are for the top-level card modules which are |
| specific to each given architecture. |
| </para> |
| </section> |
| |
| <section id="file-tree-usb-directory"> |
| <title>usb directory</title> |
| <para> |
| This contains the USB-audio driver. On the latest version, the |
| USB MIDI driver is integrated together with usb-audio driver. |
| </para> |
| </section> |
| |
| <section id="file-tree-pcmcia-directory"> |
| <title>pcmcia directory</title> |
| <para> |
| The PCMCIA, especially PCCard drivers will go here. CardBus |
| drivers will be on pci directory, because its API is identical |
| with the standard PCI cards. |
| </para> |
| </section> |
| |
| <section id="file-tree-oss-directory"> |
| <title>oss directory</title> |
| <para> |
| The OSS/Lite source files are stored here on Linux 2.6 (or |
| later) tree. (In the ALSA driver tarball, it's empty, of course :) |
| </para> |
| </section> |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Basic Flow for PCI Drivers --> |
| <!-- ****************************************************** --> |
| <chapter id="basic-flow"> |
| <title>Basic Flow for PCI Drivers</title> |
| |
| <section id="basic-flow-outline"> |
| <title>Outline</title> |
| <para> |
| The minimum flow of PCI soundcard is like the following: |
| |
| <itemizedlist> |
| <listitem><para>define the PCI ID table (see the section |
| <link linkend="pci-resource-entries"><citetitle>PCI Entries |
| </citetitle></link>).</para></listitem> |
| <listitem><para>create <function>probe()</function> callback.</para></listitem> |
| <listitem><para>create <function>remove()</function> callback.</para></listitem> |
| <listitem><para>create pci_driver table which contains the three pointers above.</para></listitem> |
| <listitem><para>create <function>init()</function> function just calling <function>pci_register_driver()</function> to register the pci_driver table defined above.</para></listitem> |
| <listitem><para>create <function>exit()</function> function to call <function>pci_unregister_driver()</function> function.</para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id="basic-flow-example"> |
| <title>Full Code Example</title> |
| <para> |
| The code example is shown below. Some parts are kept |
| unimplemented at this moment but will be filled in the |
| succeeding sections. The numbers in comment lines of |
| <function>snd_mychip_probe()</function> function are the |
| markers. |
| |
| <example> |
| <title>Basic Flow for PCI Drivers Example</title> |
| <programlisting> |
| <![CDATA[ |
| #include <sound/driver.h> |
| #include <linux/init.h> |
| #include <linux/pci.h> |
| #include <linux/slab.h> |
| #include <sound/core.h> |
| #include <sound/initval.h> |
| |
| /* module parameters (see "Module Parameters") */ |
| static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; |
| static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; |
| static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; |
| |
| /* definition of the chip-specific record */ |
| struct mychip { |
| struct snd_card *card; |
| // rest of implementation will be in the section |
| // "PCI Resource Managements" |
| }; |
| |
| /* chip-specific destructor |
| * (see "PCI Resource Managements") |
| */ |
| static int snd_mychip_free(struct mychip *chip) |
| { |
| .... // will be implemented later... |
| } |
| |
| /* component-destructor |
| * (see "Management of Cards and Components") |
| */ |
| static int snd_mychip_dev_free(struct snd_device *device) |
| { |
| return snd_mychip_free(device->device_data); |
| } |
| |
| /* chip-specific constructor |
| * (see "Management of Cards and Components") |
| */ |
| static int __devinit snd_mychip_create(struct snd_card *card, |
| struct pci_dev *pci, |
| struct mychip **rchip) |
| { |
| struct mychip *chip; |
| int err; |
| static struct snd_device_ops ops = { |
| .dev_free = snd_mychip_dev_free, |
| }; |
| |
| *rchip = NULL; |
| |
| // check PCI availability here |
| // (see "PCI Resource Managements") |
| .... |
| |
| /* allocate a chip-specific data with zero filled */ |
| chip = kzalloc(sizeof(*chip), GFP_KERNEL); |
| if (chip == NULL) |
| return -ENOMEM; |
| |
| chip->card = card; |
| |
| // rest of initialization here; will be implemented |
| // later, see "PCI Resource Managements" |
| .... |
| |
| if ((err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, |
| chip, &ops)) < 0) { |
| snd_mychip_free(chip); |
| return err; |
| } |
| |
| snd_card_set_dev(card, &pci->dev); |
| |
| *rchip = chip; |
| return 0; |
| } |
| |
| /* constructor -- see "Constructor" sub-section */ |
| static int __devinit snd_mychip_probe(struct pci_dev *pci, |
| const struct pci_device_id *pci_id) |
| { |
| static int dev; |
| struct snd_card *card; |
| struct mychip *chip; |
| int err; |
| |
| /* (1) */ |
| if (dev >= SNDRV_CARDS) |
| return -ENODEV; |
| if (!enable[dev]) { |
| dev++; |
| return -ENOENT; |
| } |
| |
| /* (2) */ |
| card = snd_card_new(index[dev], id[dev], THIS_MODULE, 0); |
| if (card == NULL) |
| return -ENOMEM; |
| |
| /* (3) */ |
| if ((err = snd_mychip_create(card, pci, &chip)) < 0) { |
| snd_card_free(card); |
| return err; |
| } |
| |
| /* (4) */ |
| strcpy(card->driver, "My Chip"); |
| strcpy(card->shortname, "My Own Chip 123"); |
| sprintf(card->longname, "%s at 0x%lx irq %i", |
| card->shortname, chip->ioport, chip->irq); |
| |
| /* (5) */ |
| .... // implemented later |
| |
| /* (6) */ |
| if ((err = snd_card_register(card)) < 0) { |
| snd_card_free(card); |
| return err; |
| } |
| |
| /* (7) */ |
| pci_set_drvdata(pci, card); |
| dev++; |
| return 0; |
| } |
| |
| /* destructor -- see "Destructor" sub-section */ |
| static void __devexit snd_mychip_remove(struct pci_dev *pci) |
| { |
| snd_card_free(pci_get_drvdata(pci)); |
| pci_set_drvdata(pci, NULL); |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </section> |
| |
| <section id="basic-flow-constructor"> |
| <title>Constructor</title> |
| <para> |
| The real constructor of PCI drivers is probe callback. The |
| probe callback and other component-constructors which are called |
| from probe callback should be defined with |
| <parameter>__devinit</parameter> prefix. You |
| cannot use <parameter>__init</parameter> prefix for them, |
| because any PCI device could be a hotplug device. |
| </para> |
| |
| <para> |
| In the probe callback, the following scheme is often used. |
| </para> |
| |
| <section id="basic-flow-constructor-device-index"> |
| <title>1) Check and increment the device index.</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int dev; |
| .... |
| if (dev >= SNDRV_CARDS) |
| return -ENODEV; |
| if (!enable[dev]) { |
| dev++; |
| return -ENOENT; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where enable[dev] is the module option. |
| </para> |
| |
| <para> |
| At each time probe callback is called, check the |
| availability of the device. If not available, simply increment |
| the device index and returns. dev will be incremented also |
| later (<link |
| linkend="basic-flow-constructor-set-pci"><citetitle>step |
| 7</citetitle></link>). |
| </para> |
| </section> |
| |
| <section id="basic-flow-constructor-create-card"> |
| <title>2) Create a card instance</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_card *card; |
| .... |
| card = snd_card_new(index[dev], id[dev], THIS_MODULE, 0); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The detail will be explained in the section |
| <link linkend="card-management-card-instance"><citetitle> |
| Management of Cards and Components</citetitle></link>. |
| </para> |
| </section> |
| |
| <section id="basic-flow-constructor-create-main"> |
| <title>3) Create a main component</title> |
| <para> |
| In this part, the PCI resources are allocated. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct mychip *chip; |
| .... |
| if ((err = snd_mychip_create(card, pci, &chip)) < 0) { |
| snd_card_free(card); |
| return err; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| The detail will be explained in the section <link |
| linkend="pci-resource"><citetitle>PCI Resource |
| Managements</citetitle></link>. |
| </para> |
| </section> |
| |
| <section id="basic-flow-constructor-main-component"> |
| <title>4) Set the driver ID and name strings.</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| strcpy(card->driver, "My Chip"); |
| strcpy(card->shortname, "My Own Chip 123"); |
| sprintf(card->longname, "%s at 0x%lx irq %i", |
| card->shortname, chip->ioport, chip->irq); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| The driver field holds the minimal ID string of the |
| chip. This is referred by alsa-lib's configurator, so keep it |
| simple but unique. |
| Even the same driver can have different driver IDs to |
| distinguish the functionality of each chip type. |
| </para> |
| |
| <para> |
| The shortname field is a string shown as more verbose |
| name. The longname field contains the information which is |
| shown in <filename>/proc/asound/cards</filename>. |
| </para> |
| </section> |
| |
| <section id="basic-flow-constructor-create-other"> |
| <title>5) Create other components, such as mixer, MIDI, etc.</title> |
| <para> |
| Here you define the basic components such as |
| <link linkend="pcm-interface"><citetitle>PCM</citetitle></link>, |
| mixer (e.g. <link linkend="api-ac97"><citetitle>AC97</citetitle></link>), |
| MIDI (e.g. <link linkend="midi-interface"><citetitle>MPU-401</citetitle></link>), |
| and other interfaces. |
| Also, if you want a <link linkend="proc-interface"><citetitle>proc |
| file</citetitle></link>, define it here, too. |
| </para> |
| </section> |
| |
| <section id="basic-flow-constructor-register-card"> |
| <title>6) Register the card instance.</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| if ((err = snd_card_register(card)) < 0) { |
| snd_card_free(card); |
| return err; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Will be explained in the section <link |
| linkend="card-management-registration"><citetitle>Management |
| of Cards and Components</citetitle></link>, too. |
| </para> |
| </section> |
| |
| <section id="basic-flow-constructor-set-pci"> |
| <title>7) Set the PCI driver data and return zero.</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| pci_set_drvdata(pci, card); |
| dev++; |
| return 0; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| In the above, the card record is stored. This pointer is |
| referred in the remove callback and power-management |
| callbacks, too. |
| </para> |
| </section> |
| </section> |
| |
| <section id="basic-flow-destructor"> |
| <title>Destructor</title> |
| <para> |
| The destructor, remove callback, simply releases the card |
| instance. Then the ALSA middle layer will release all the |
| attached components automatically. |
| </para> |
| |
| <para> |
| It would be typically like the following: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void __devexit snd_mychip_remove(struct pci_dev *pci) |
| { |
| snd_card_free(pci_get_drvdata(pci)); |
| pci_set_drvdata(pci, NULL); |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| The above code assumes that the card pointer is set to the PCI |
| driver data. |
| </para> |
| </section> |
| |
| <section id="basic-flow-header-files"> |
| <title>Header Files</title> |
| <para> |
| For the above example, at least the following include files |
| are necessary. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| #include <sound/driver.h> |
| #include <linux/init.h> |
| #include <linux/pci.h> |
| #include <linux/slab.h> |
| #include <sound/core.h> |
| #include <sound/initval.h> |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where the last one is necessary only when module options are |
| defined in the source file. If the codes are split to several |
| files, the file without module options don't need them. |
| </para> |
| |
| <para> |
| In addition to them, you'll need |
| <filename><linux/interrupt.h></filename> for the interrupt |
| handling, and <filename><asm/io.h></filename> for the i/o |
| access. If you use <function>mdelay()</function> or |
| <function>udelay()</function> functions, you'll need to include |
| <filename><linux/delay.h></filename>, too. |
| </para> |
| |
| <para> |
| The ALSA interfaces like PCM or control API are defined in other |
| header files as <filename><sound/xxx.h></filename>. |
| They have to be included after |
| <filename><sound/core.h></filename>. |
| </para> |
| |
| </section> |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Management of Cards and Components --> |
| <!-- ****************************************************** --> |
| <chapter id="card-management"> |
| <title>Management of Cards and Components</title> |
| |
| <section id="card-management-card-instance"> |
| <title>Card Instance</title> |
| <para> |
| For each soundcard, a <quote>card</quote> record must be allocated. |
| </para> |
| |
| <para> |
| A card record is the headquarters of the soundcard. It manages |
| the list of whole devices (components) on the soundcard, such as |
| PCM, mixers, MIDI, synthesizer, and so on. Also, the card |
| record holds the ID and the name strings of the card, manages |
| the root of proc files, and controls the power-management states |
| and hotplug disconnections. The component list on the card |
| record is used to manage the proper releases of resources at |
| destruction. |
| </para> |
| |
| <para> |
| As mentioned above, to create a card instance, call |
| <function>snd_card_new()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_card *card; |
| card = snd_card_new(index, id, module, extra_size); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The function takes four arguments, the card-index number, the |
| id string, the module pointer (usually |
| <constant>THIS_MODULE</constant>), |
| and the size of extra-data space. The last argument is used to |
| allocate card->private_data for the |
| chip-specific data. Note that this data |
| <emphasis>is</emphasis> allocated by |
| <function>snd_card_new()</function>. |
| </para> |
| </section> |
| |
| <section id="card-management-component"> |
| <title>Components</title> |
| <para> |
| After the card is created, you can attach the components |
| (devices) to the card instance. On ALSA driver, a component is |
| represented as a struct <structname>snd_device</structname> object. |
| A component can be a PCM instance, a control interface, a raw |
| MIDI interface, etc. Each of such instances has one component |
| entry. |
| </para> |
| |
| <para> |
| A component can be created via |
| <function>snd_device_new()</function> function. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_device_new(card, SNDRV_DEV_XXX, chip, &ops); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| This takes the card pointer, the device-level |
| (<constant>SNDRV_DEV_XXX</constant>), the data pointer, and the |
| callback pointers (<parameter>&ops</parameter>). The |
| device-level defines the type of components and the order of |
| registration and de-registration. For most of components, the |
| device-level is already defined. For a user-defined component, |
| you can use <constant>SNDRV_DEV_LOWLEVEL</constant>. |
| </para> |
| |
| <para> |
| This function itself doesn't allocate the data space. The data |
| must be allocated manually beforehand, and its pointer is passed |
| as the argument. This pointer is used as the identifier |
| (<parameter>chip</parameter> in the above example) for the |
| instance. |
| </para> |
| |
| <para> |
| Each ALSA pre-defined component such as ac97 or pcm calls |
| <function>snd_device_new()</function> inside its |
| constructor. The destructor for each component is defined in the |
| callback pointers. Hence, you don't need to take care of |
| calling a destructor for such a component. |
| </para> |
| |
| <para> |
| If you would like to create your own component, you need to |
| set the destructor function to dev_free callback in |
| <parameter>ops</parameter>, so that it can be released |
| automatically via <function>snd_card_free()</function>. The |
| example will be shown later as an implementation of a |
| chip-specific data. |
| </para> |
| </section> |
| |
| <section id="card-management-chip-specific"> |
| <title>Chip-Specific Data</title> |
| <para> |
| The chip-specific information, e.g. the i/o port address, its |
| resource pointer, or the irq number, is stored in the |
| chip-specific record. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct mychip { |
| .... |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| In general, there are two ways to allocate the chip record. |
| </para> |
| |
| <section id="card-management-chip-specific-snd-card-new"> |
| <title>1. Allocating via <function>snd_card_new()</function>.</title> |
| <para> |
| As mentioned above, you can pass the extra-data-length to the 4th argument of <function>snd_card_new()</function>, i.e. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| card = snd_card_new(index[dev], id[dev], THIS_MODULE, sizeof(struct mychip)); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| whether struct <structname>mychip</structname> is the type of the chip record. |
| </para> |
| |
| <para> |
| In return, the allocated record can be accessed as |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct mychip *chip = (struct mychip *)card->private_data; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| With this method, you don't have to allocate twice. |
| The record is released together with the card instance. |
| </para> |
| </section> |
| |
| <section id="card-management-chip-specific-allocate-extra"> |
| <title>2. Allocating an extra device.</title> |
| |
| <para> |
| After allocating a card instance via |
| <function>snd_card_new()</function> (with |
| <constant>NULL</constant> on the 4th arg), call |
| <function>kzalloc()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_card *card; |
| struct mychip *chip; |
| card = snd_card_new(index[dev], id[dev], THIS_MODULE, NULL); |
| ..... |
| chip = kzalloc(sizeof(*chip), GFP_KERNEL); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The chip record should have the field to hold the card |
| pointer at least, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct mychip { |
| struct snd_card *card; |
| .... |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Then, set the card pointer in the returned chip instance. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| chip->card = card; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Next, initialize the fields, and register this chip |
| record as a low-level device with a specified |
| <parameter>ops</parameter>, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct snd_device_ops ops = { |
| .dev_free = snd_mychip_dev_free, |
| }; |
| .... |
| snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| <function>snd_mychip_dev_free()</function> is the |
| device-destructor function, which will call the real |
| destructor. |
| </para> |
| |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_mychip_dev_free(struct snd_device *device) |
| { |
| return snd_mychip_free(device->device_data); |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where <function>snd_mychip_free()</function> is the real destructor. |
| </para> |
| </section> |
| </section> |
| |
| <section id="card-management-registration"> |
| <title>Registration and Release</title> |
| <para> |
| After all components are assigned, register the card instance |
| by calling <function>snd_card_register()</function>. The access |
| to the device files are enabled at this point. That is, before |
| <function>snd_card_register()</function> is called, the |
| components are safely inaccessible from external side. If this |
| call fails, exit the probe function after releasing the card via |
| <function>snd_card_free()</function>. |
| </para> |
| |
| <para> |
| For releasing the card instance, you can call simply |
| <function>snd_card_free()</function>. As already mentioned, all |
| components are released automatically by this call. |
| </para> |
| |
| <para> |
| As further notes, the destructors (both |
| <function>snd_mychip_dev_free</function> and |
| <function>snd_mychip_free</function>) cannot be defined with |
| <parameter>__devexit</parameter> prefix, because they may be |
| called from the constructor, too, at the false path. |
| </para> |
| |
| <para> |
| For a device which allows hotplugging, you can use |
| <function>snd_card_free_in_thread</function>. This one will |
| postpone the destruction and wait in a kernel-thread until all |
| devices are closed. |
| </para> |
| |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- PCI Resource Managements --> |
| <!-- ****************************************************** --> |
| <chapter id="pci-resource"> |
| <title>PCI Resource Managements</title> |
| |
| <section id="pci-resource-example"> |
| <title>Full Code Example</title> |
| <para> |
| In this section, we'll finish the chip-specific constructor, |
| destructor and PCI entries. The example code is shown first, |
| below. |
| |
| <example> |
| <title>PCI Resource Managements Example</title> |
| <programlisting> |
| <![CDATA[ |
| struct mychip { |
| struct snd_card *card; |
| struct pci_dev *pci; |
| |
| unsigned long port; |
| int irq; |
| }; |
| |
| static int snd_mychip_free(struct mychip *chip) |
| { |
| /* disable hardware here if any */ |
| .... // (not implemented in this document) |
| |
| /* release the irq */ |
| if (chip->irq >= 0) |
| free_irq(chip->irq, (void *)chip); |
| /* release the i/o ports & memory */ |
| pci_release_regions(chip->pci); |
| /* disable the PCI entry */ |
| pci_disable_device(chip->pci); |
| /* release the data */ |
| kfree(chip); |
| return 0; |
| } |
| |
| /* chip-specific constructor */ |
| static int __devinit snd_mychip_create(struct snd_card *card, |
| struct pci_dev *pci, |
| struct mychip **rchip) |
| { |
| struct mychip *chip; |
| int err; |
| static struct snd_device_ops ops = { |
| .dev_free = snd_mychip_dev_free, |
| }; |
| |
| *rchip = NULL; |
| |
| /* initialize the PCI entry */ |
| if ((err = pci_enable_device(pci)) < 0) |
| return err; |
| /* check PCI availability (28bit DMA) */ |
| if (pci_set_dma_mask(pci, 0x0fffffff) < 0 || |
| pci_set_consistent_dma_mask(pci, 0x0fffffff) < 0) { |
| printk(KERN_ERR "error to set 28bit mask DMA\n"); |
| pci_disable_device(pci); |
| return -ENXIO; |
| } |
| |
| chip = kzalloc(sizeof(*chip), GFP_KERNEL); |
| if (chip == NULL) { |
| pci_disable_device(pci); |
| return -ENOMEM; |
| } |
| |
| /* initialize the stuff */ |
| chip->card = card; |
| chip->pci = pci; |
| chip->irq = -1; |
| |
| /* (1) PCI resource allocation */ |
| if ((err = pci_request_regions(pci, "My Chip")) < 0) { |
| kfree(chip); |
| pci_disable_device(pci); |
| return err; |
| } |
| chip->port = pci_resource_start(pci, 0); |
| if (request_irq(pci->irq, snd_mychip_interrupt, |
| SA_INTERRUPT|SA_SHIRQ, "My Chip", chip)) { |
| printk(KERN_ERR "cannot grab irq %d\n", pci->irq); |
| snd_mychip_free(chip); |
| return -EBUSY; |
| } |
| chip->irq = pci->irq; |
| |
| /* (2) initialization of the chip hardware */ |
| .... // (not implemented in this document) |
| |
| if ((err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, |
| chip, &ops)) < 0) { |
| snd_mychip_free(chip); |
| return err; |
| } |
| |
| snd_card_set_dev(card, &pci->dev); |
| |
| *rchip = chip; |
| return 0; |
| } |
| |
| /* PCI IDs */ |
| static struct pci_device_id snd_mychip_ids[] = { |
| { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, |
| PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, |
| .... |
| { 0, } |
| }; |
| MODULE_DEVICE_TABLE(pci, snd_mychip_ids); |
| |
| /* pci_driver definition */ |
| static struct pci_driver driver = { |
| .name = "My Own Chip", |
| .id_table = snd_mychip_ids, |
| .probe = snd_mychip_probe, |
| .remove = __devexit_p(snd_mychip_remove), |
| }; |
| |
| /* initialization of the module */ |
| static int __init alsa_card_mychip_init(void) |
| { |
| return pci_register_driver(&driver); |
| } |
| |
| /* clean up the module */ |
| static void __exit alsa_card_mychip_exit(void) |
| { |
| pci_unregister_driver(&driver); |
| } |
| |
| module_init(alsa_card_mychip_init) |
| module_exit(alsa_card_mychip_exit) |
| |
| EXPORT_NO_SYMBOLS; /* for old kernels only */ |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </section> |
| |
| <section id="pci-resource-some-haftas"> |
| <title>Some Hafta's</title> |
| <para> |
| The allocation of PCI resources is done in the |
| <function>probe()</function> function, and usually an extra |
| <function>xxx_create()</function> function is written for this |
| purpose. |
| </para> |
| |
| <para> |
| In the case of PCI devices, you have to call at first |
| <function>pci_enable_device()</function> function before |
| allocating resources. Also, you need to set the proper PCI DMA |
| mask to limit the accessed i/o range. In some cases, you might |
| need to call <function>pci_set_master()</function> function, |
| too. |
| </para> |
| |
| <para> |
| Suppose the 28bit mask, and the code to be added would be like: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| if ((err = pci_enable_device(pci)) < 0) |
| return err; |
| if (pci_set_dma_mask(pci, 0x0fffffff) < 0 || |
| pci_set_consistent_dma_mask(pci, 0x0fffffff) < 0) { |
| printk(KERN_ERR "error to set 28bit mask DMA\n"); |
| pci_disable_device(pci); |
| return -ENXIO; |
| } |
| |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| <section id="pci-resource-resource-allocation"> |
| <title>Resource Allocation</title> |
| <para> |
| The allocation of I/O ports and irqs are done via standard kernel |
| functions. Unlike ALSA ver.0.5.x., there are no helpers for |
| that. And these resources must be released in the destructor |
| function (see below). Also, on ALSA 0.9.x, you don't need to |
| allocate (pseudo-)DMA for PCI like ALSA 0.5.x. |
| </para> |
| |
| <para> |
| Now assume that this PCI device has an I/O port with 8 bytes |
| and an interrupt. Then struct <structname>mychip</structname> will have the |
| following fields: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct mychip { |
| struct snd_card *card; |
| |
| unsigned long port; |
| int irq; |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| For an i/o port (and also a memory region), you need to have |
| the resource pointer for the standard resource management. For |
| an irq, you have to keep only the irq number (integer). But you |
| need to initialize this number as -1 before actual allocation, |
| since irq 0 is valid. The port address and its resource pointer |
| can be initialized as null by |
| <function>kzalloc()</function> automatically, so you |
| don't have to take care of resetting them. |
| </para> |
| |
| <para> |
| The allocation of an i/o port is done like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| if ((err = pci_request_regions(pci, "My Chip")) < 0) { |
| kfree(chip); |
| pci_disable_device(pci); |
| return err; |
| } |
| chip->port = pci_resource_start(pci, 0); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| <!-- obsolete --> |
| It will reserve the i/o port region of 8 bytes of the given |
| PCI device. The returned value, chip->res_port, is allocated |
| via <function>kmalloc()</function> by |
| <function>request_region()</function>. The pointer must be |
| released via <function>kfree()</function>, but there is some |
| problem regarding this. This issue will be explained more below. |
| </para> |
| |
| <para> |
| The allocation of an interrupt source is done like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| if (request_irq(pci->irq, snd_mychip_interrupt, |
| SA_INTERRUPT|SA_SHIRQ, "My Chip", chip)) { |
| printk(KERN_ERR "cannot grab irq %d\n", pci->irq); |
| snd_mychip_free(chip); |
| return -EBUSY; |
| } |
| chip->irq = pci->irq; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where <function>snd_mychip_interrupt()</function> is the |
| interrupt handler defined <link |
| linkend="pcm-interface-interrupt-handler"><citetitle>later</citetitle></link>. |
| Note that chip->irq should be defined |
| only when <function>request_irq()</function> succeeded. |
| </para> |
| |
| <para> |
| On the PCI bus, the interrupts can be shared. Thus, |
| <constant>SA_SHIRQ</constant> is given as the interrupt flag of |
| <function>request_irq()</function>. |
| </para> |
| |
| <para> |
| The last argument of <function>request_irq()</function> is the |
| data pointer passed to the interrupt handler. Usually, the |
| chip-specific record is used for that, but you can use what you |
| like, too. |
| </para> |
| |
| <para> |
| I won't define the detail of the interrupt handler at this |
| point, but at least its appearance can be explained now. The |
| interrupt handler looks usually like the following: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id, |
| struct pt_regs *regs) |
| { |
| struct mychip *chip = dev_id; |
| .... |
| return IRQ_HANDLED; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Now let's write the corresponding destructor for the resources |
| above. The role of destructor is simple: disable the hardware |
| (if already activated) and release the resources. So far, we |
| have no hardware part, so the disabling is not written here. |
| </para> |
| |
| <para> |
| For releasing the resources, <quote>check-and-release</quote> |
| method is a safer way. For the interrupt, do like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| if (chip->irq >= 0) |
| free_irq(chip->irq, (void *)chip); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| Since the irq number can start from 0, you should initialize |
| chip->irq with a negative value (e.g. -1), so that you can |
| check the validity of the irq number as above. |
| </para> |
| |
| <para> |
| When you requested I/O ports or memory regions via |
| <function>pci_request_region()</function> or |
| <function>pci_request_regions()</function> like this example, |
| release the resource(s) using the corresponding function, |
| <function>pci_release_region()</function> or |
| <function>pci_release_regions()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| pci_release_regions(chip->pci); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| When you requested manually via <function>request_region()</function> |
| or <function>request_mem_region</function>, you can release it via |
| <function>release_resource()</function>. Suppose that you keep |
| the resource pointer returned from <function>request_region()</function> |
| in chip->res_port, the release procedure looks like below: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| release_and_free_resource(chip->res_port); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Don't forget to call <function>pci_disable_device()</function> |
| before all finished. |
| </para> |
| |
| <para> |
| And finally, release the chip-specific record. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| kfree(chip); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Again, remember that you cannot |
| set <parameter>__devexit</parameter> prefix for this destructor. |
| </para> |
| |
| <para> |
| We didn't implement the hardware-disabling part in the above. |
| If you need to do this, please note that the destructor may be |
| called even before the initialization of the chip is completed. |
| It would be better to have a flag to skip the hardware-disabling |
| if the hardware was not initialized yet. |
| </para> |
| |
| <para> |
| When the chip-data is assigned to the card using |
| <function>snd_device_new()</function> with |
| <constant>SNDRV_DEV_LOWLELVEL</constant> , its destructor is |
| called at the last. That is, it is assured that all other |
| components like PCMs and controls have been already released. |
| You don't have to call stopping PCMs, etc. explicitly, but just |
| stop the hardware in the low-level. |
| </para> |
| |
| <para> |
| The management of a memory-mapped region is almost as same as |
| the management of an i/o port. You'll need three fields like |
| the following: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct mychip { |
| .... |
| unsigned long iobase_phys; |
| void __iomem *iobase_virt; |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| and the allocation would be like below: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| if ((err = pci_request_regions(pci, "My Chip")) < 0) { |
| kfree(chip); |
| return err; |
| } |
| chip->iobase_phys = pci_resource_start(pci, 0); |
| chip->iobase_virt = ioremap_nocache(chip->iobase_phys, |
| pci_resource_len(pci, 0)); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| and the corresponding destructor would be: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_mychip_free(struct mychip *chip) |
| { |
| .... |
| if (chip->iobase_virt) |
| iounmap(chip->iobase_virt); |
| .... |
| pci_release_regions(chip->pci); |
| .... |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| </section> |
| |
| <section id="pci-resource-device-struct"> |
| <title>Registration of Device Struct</title> |
| <para> |
| At some point, typically after calling <function>snd_device_new()</function>, |
| you need to register the struct <structname>device</structname> of the chip |
| you're handling for udev and co. ALSA provides a macro for compatibility with |
| older kernels. Simply call like the following: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_card_set_dev(card, &pci->dev); |
| ]]> |
| </programlisting> |
| </informalexample> |
| so that it stores the PCI's device pointer to the card. This will be |
| referred by ALSA core functions later when the devices are registered. |
| </para> |
| <para> |
| In the case of non-PCI, pass the proper device struct pointer of the BUS |
| instead. (In the case of legacy ISA without PnP, you don't have to do |
| anything.) |
| </para> |
| </section> |
| |
| <section id="pci-resource-entries"> |
| <title>PCI Entries</title> |
| <para> |
| So far, so good. Let's finish the rest of missing PCI |
| stuffs. At first, we need a |
| <structname>pci_device_id</structname> table for this |
| chipset. It's a table of PCI vendor/device ID number, and some |
| masks. |
| </para> |
| |
| <para> |
| For example, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct pci_device_id snd_mychip_ids[] = { |
| { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, |
| PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, |
| .... |
| { 0, } |
| }; |
| MODULE_DEVICE_TABLE(pci, snd_mychip_ids); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The first and second fields of |
| <structname>pci_device_id</structname> struct are the vendor and |
| device IDs. If you have nothing special to filter the matching |
| devices, you can use the rest of fields like above. The last |
| field of <structname>pci_device_id</structname> struct is a |
| private data for this entry. You can specify any value here, for |
| example, to tell the type of different operations per each |
| device IDs. Such an example is found in intel8x0 driver. |
| </para> |
| |
| <para> |
| The last entry of this list is the terminator. You must |
| specify this all-zero entry. |
| </para> |
| |
| <para> |
| Then, prepare the <structname>pci_driver</structname> record: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct pci_driver driver = { |
| .name = "My Own Chip", |
| .id_table = snd_mychip_ids, |
| .probe = snd_mychip_probe, |
| .remove = __devexit_p(snd_mychip_remove), |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The <structfield>probe</structfield> and |
| <structfield>remove</structfield> functions are what we already |
| defined in |
| the previous sections. The <structfield>remove</structfield> should |
| be defined with |
| <function>__devexit_p()</function> macro, so that it's not |
| defined for built-in (and non-hot-pluggable) case. The |
| <structfield>name</structfield> |
| field is the name string of this device. Note that you must not |
| use a slash <quote>/</quote> in this string. |
| </para> |
| |
| <para> |
| And at last, the module entries: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int __init alsa_card_mychip_init(void) |
| { |
| return pci_register_driver(&driver); |
| } |
| |
| static void __exit alsa_card_mychip_exit(void) |
| { |
| pci_unregister_driver(&driver); |
| } |
| |
| module_init(alsa_card_mychip_init) |
| module_exit(alsa_card_mychip_exit) |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Note that these module entries are tagged with |
| <parameter>__init</parameter> and |
| <parameter>__exit</parameter> prefixes, not |
| <parameter>__devinit</parameter> nor |
| <parameter>__devexit</parameter>. |
| </para> |
| |
| <para> |
| Oh, one thing was forgotten. If you have no exported symbols, |
| you need to declare it on 2.2 or 2.4 kernels (on 2.6 kernels |
| it's not necessary, though). |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| EXPORT_NO_SYMBOLS; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| That's all! |
| </para> |
| </section> |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- PCM Interface --> |
| <!-- ****************************************************** --> |
| <chapter id="pcm-interface"> |
| <title>PCM Interface</title> |
| |
| <section id="pcm-interface-general"> |
| <title>General</title> |
| <para> |
| The PCM middle layer of ALSA is quite powerful and it is only |
| necessary for each driver to implement the low-level functions |
| to access its hardware. |
| </para> |
| |
| <para> |
| For accessing to the PCM layer, you need to include |
| <filename><sound/pcm.h></filename> above all. In addition, |
| <filename><sound/pcm_params.h></filename> might be needed |
| if you access to some functions related with hw_param. |
| </para> |
| |
| <para> |
| Each card device can have up to four pcm instances. A pcm |
| instance corresponds to a pcm device file. The limitation of |
| number of instances comes only from the available bit size of |
| the linux's device number. Once when 64bit device number is |
| used, we'll have more available pcm instances. |
| </para> |
| |
| <para> |
| A pcm instance consists of pcm playback and capture streams, |
| and each pcm stream consists of one or more pcm substreams. Some |
| soundcard supports the multiple-playback function. For example, |
| emu10k1 has a PCM playback of 32 stereo substreams. In this case, at |
| each open, a free substream is (usually) automatically chosen |
| and opened. Meanwhile, when only one substream exists and it was |
| already opened, the succeeding open will result in the blocking |
| or the error with <constant>EAGAIN</constant> according to the |
| file open mode. But you don't have to know the detail in your |
| driver. The PCM middle layer will take all such jobs. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-example"> |
| <title>Full Code Example</title> |
| <para> |
| The example code below does not include any hardware access |
| routines but shows only the skeleton, how to build up the PCM |
| interfaces. |
| |
| <example> |
| <title>PCM Example Code</title> |
| <programlisting> |
| <![CDATA[ |
| #include <sound/pcm.h> |
| .... |
| |
| /* hardware definition */ |
| static struct snd_pcm_hardware snd_mychip_playback_hw = { |
| .info = (SNDRV_PCM_INFO_MMAP | |
| SNDRV_PCM_INFO_INTERLEAVED | |
| SNDRV_PCM_INFO_BLOCK_TRANSFER | |
| SNDRV_PCM_INFO_MMAP_VALID), |
| .formats = SNDRV_PCM_FMTBIT_S16_LE, |
| .rates = SNDRV_PCM_RATE_8000_48000, |
| .rate_min = 8000, |
| .rate_max = 48000, |
| .channels_min = 2, |
| .channels_max = 2, |
| .buffer_bytes_max = 32768, |
| .period_bytes_min = 4096, |
| .period_bytes_max = 32768, |
| .periods_min = 1, |
| .periods_max = 1024, |
| }; |
| |
| /* hardware definition */ |
| static struct snd_pcm_hardware snd_mychip_capture_hw = { |
| .info = (SNDRV_PCM_INFO_MMAP | |
| SNDRV_PCM_INFO_INTERLEAVED | |
| SNDRV_PCM_INFO_BLOCK_TRANSFER | |
| SNDRV_PCM_INFO_MMAP_VALID), |
| .formats = SNDRV_PCM_FMTBIT_S16_LE, |
| .rates = SNDRV_PCM_RATE_8000_48000, |
| .rate_min = 8000, |
| .rate_max = 48000, |
| .channels_min = 2, |
| .channels_max = 2, |
| .buffer_bytes_max = 32768, |
| .period_bytes_min = 4096, |
| .period_bytes_max = 32768, |
| .periods_min = 1, |
| .periods_max = 1024, |
| }; |
| |
| /* open callback */ |
| static int snd_mychip_playback_open(struct snd_pcm_substream *substream) |
| { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| struct snd_pcm_runtime *runtime = substream->runtime; |
| |
| runtime->hw = snd_mychip_playback_hw; |
| // more hardware-initialization will be done here |
| return 0; |
| } |
| |
| /* close callback */ |
| static int snd_mychip_playback_close(struct snd_pcm_substream *substream) |
| { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| // the hardware-specific codes will be here |
| return 0; |
| |
| } |
| |
| /* open callback */ |
| static int snd_mychip_capture_open(struct snd_pcm_substream *substream) |
| { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| struct snd_pcm_runtime *runtime = substream->runtime; |
| |
| runtime->hw = snd_mychip_capture_hw; |
| // more hardware-initialization will be done here |
| return 0; |
| } |
| |
| /* close callback */ |
| static int snd_mychip_capture_close(struct snd_pcm_substream *substream) |
| { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| // the hardware-specific codes will be here |
| return 0; |
| |
| } |
| |
| /* hw_params callback */ |
| static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream, |
| struct snd_pcm_hw_params *hw_params) |
| { |
| return snd_pcm_lib_malloc_pages(substream, |
| params_buffer_bytes(hw_params)); |
| } |
| |
| /* hw_free callback */ |
| static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream) |
| { |
| return snd_pcm_lib_free_pages(substream); |
| } |
| |
| /* prepare callback */ |
| static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream) |
| { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| struct snd_pcm_runtime *runtime = substream->runtime; |
| |
| /* set up the hardware with the current configuration |
| * for example... |
| */ |
| mychip_set_sample_format(chip, runtime->format); |
| mychip_set_sample_rate(chip, runtime->rate); |
| mychip_set_channels(chip, runtime->channels); |
| mychip_set_dma_setup(chip, runtime->dma_area, |
| chip->buffer_size, |
| chip->period_size); |
| return 0; |
| } |
| |
| /* trigger callback */ |
| static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream, |
| int cmd) |
| { |
| switch (cmd) { |
| case SNDRV_PCM_TRIGGER_START: |
| // do something to start the PCM engine |
| break; |
| case SNDRV_PCM_TRIGGER_STOP: |
| // do something to stop the PCM engine |
| break; |
| default: |
| return -EINVAL; |
| } |
| } |
| |
| /* pointer callback */ |
| static snd_pcm_uframes_t |
| snd_mychip_pcm_pointer(struct snd_pcm_substream *substream) |
| { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| unsigned int current_ptr; |
| |
| /* get the current hardware pointer */ |
| current_ptr = mychip_get_hw_pointer(chip); |
| return current_ptr; |
| } |
| |
| /* operators */ |
| static struct snd_pcm_ops snd_mychip_playback_ops = { |
| .open = snd_mychip_playback_open, |
| .close = snd_mychip_playback_close, |
| .ioctl = snd_pcm_lib_ioctl, |
| .hw_params = snd_mychip_pcm_hw_params, |
| .hw_free = snd_mychip_pcm_hw_free, |
| .prepare = snd_mychip_pcm_prepare, |
| .trigger = snd_mychip_pcm_trigger, |
| .pointer = snd_mychip_pcm_pointer, |
| }; |
| |
| /* operators */ |
| static struct snd_pcm_ops snd_mychip_capture_ops = { |
| .open = snd_mychip_capture_open, |
| .close = snd_mychip_capture_close, |
| .ioctl = snd_pcm_lib_ioctl, |
| .hw_params = snd_mychip_pcm_hw_params, |
| .hw_free = snd_mychip_pcm_hw_free, |
| .prepare = snd_mychip_pcm_prepare, |
| .trigger = snd_mychip_pcm_trigger, |
| .pointer = snd_mychip_pcm_pointer, |
| }; |
| |
| /* |
| * definitions of capture are omitted here... |
| */ |
| |
| /* create a pcm device */ |
| static int __devinit snd_mychip_new_pcm(struct mychip *chip) |
| { |
| struct snd_pcm *pcm; |
| int err; |
| |
| if ((err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, |
| &pcm)) < 0) |
| return err; |
| pcm->private_data = chip; |
| strcpy(pcm->name, "My Chip"); |
| chip->pcm = pcm; |
| /* set operators */ |
| snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, |
| &snd_mychip_playback_ops); |
| snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, |
| &snd_mychip_capture_ops); |
| /* pre-allocation of buffers */ |
| /* NOTE: this may fail */ |
| snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, |
| snd_dma_pci_data(chip->pci), |
| 64*1024, 64*1024); |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </section> |
| |
| <section id="pcm-interface-constructor"> |
| <title>Constructor</title> |
| <para> |
| A pcm instance is allocated by <function>snd_pcm_new()</function> |
| function. It would be better to create a constructor for pcm, |
| namely, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int __devinit snd_mychip_new_pcm(struct mychip *chip) |
| { |
| struct snd_pcm *pcm; |
| int err; |
| |
| if ((err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, |
| &pcm)) < 0) |
| return err; |
| pcm->private_data = chip; |
| strcpy(pcm->name, "My Chip"); |
| chip->pcm = pcm; |
| .... |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The <function>snd_pcm_new()</function> function takes the four |
| arguments. The first argument is the card pointer to which this |
| pcm is assigned, and the second is the ID string. |
| </para> |
| |
| <para> |
| The third argument (<parameter>index</parameter>, 0 in the |
| above) is the index of this new pcm. It begins from zero. When |
| you will create more than one pcm instances, specify the |
| different numbers in this argument. For example, |
| <parameter>index</parameter> = 1 for the second PCM device. |
| </para> |
| |
| <para> |
| The fourth and fifth arguments are the number of substreams |
| for playback and capture, respectively. Here both 1 are given in |
| the above example. When no playback or no capture is available, |
| pass 0 to the corresponding argument. |
| </para> |
| |
| <para> |
| If a chip supports multiple playbacks or captures, you can |
| specify more numbers, but they must be handled properly in |
| open/close, etc. callbacks. When you need to know which |
| substream you are referring to, then it can be obtained from |
| struct <structname>snd_pcm_substream</structname> data passed to each callback |
| as follows: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_pcm_substream *substream; |
| int index = substream->number; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| After the pcm is created, you need to set operators for each |
| pcm stream. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, |
| &snd_mychip_playback_ops); |
| snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, |
| &snd_mychip_capture_ops); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The operators are defined typically like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct snd_pcm_ops snd_mychip_playback_ops = { |
| .open = snd_mychip_pcm_open, |
| .close = snd_mychip_pcm_close, |
| .ioctl = snd_pcm_lib_ioctl, |
| .hw_params = snd_mychip_pcm_hw_params, |
| .hw_free = snd_mychip_pcm_hw_free, |
| .prepare = snd_mychip_pcm_prepare, |
| .trigger = snd_mychip_pcm_trigger, |
| .pointer = snd_mychip_pcm_pointer, |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| Each of callbacks is explained in the subsection |
| <link linkend="pcm-interface-operators"><citetitle> |
| Operators</citetitle></link>. |
| </para> |
| |
| <para> |
| After setting the operators, most likely you'd like to |
| pre-allocate the buffer. For the pre-allocation, simply call |
| the following: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, |
| snd_dma_pci_data(chip->pci), |
| 64*1024, 64*1024); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| It will allocate up to 64kB buffer as default. The details of |
| buffer management will be described in the later section <link |
| linkend="buffer-and-memory"><citetitle>Buffer and Memory |
| Management</citetitle></link>. |
| </para> |
| |
| <para> |
| Additionally, you can set some extra information for this pcm |
| in pcm->info_flags. |
| The available values are defined as |
| <constant>SNDRV_PCM_INFO_XXX</constant> in |
| <filename><sound/asound.h></filename>, which is used for |
| the hardware definition (described later). When your soundchip |
| supports only half-duplex, specify like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| <section id="pcm-interface-destructor"> |
| <title>... And the Destructor?</title> |
| <para> |
| The destructor for a pcm instance is not always |
| necessary. Since the pcm device will be released by the middle |
| layer code automatically, you don't have to call destructor |
| explicitly. |
| </para> |
| |
| <para> |
| The destructor would be necessary when you created some |
| special records internally and need to release them. In such a |
| case, set the destructor function to |
| pcm->private_free: |
| |
| <example> |
| <title>PCM Instance with a Destructor</title> |
| <programlisting> |
| <![CDATA[ |
| static void mychip_pcm_free(struct snd_pcm *pcm) |
| { |
| struct mychip *chip = snd_pcm_chip(pcm); |
| /* free your own data */ |
| kfree(chip->my_private_pcm_data); |
| // do what you like else |
| .... |
| } |
| |
| static int __devinit snd_mychip_new_pcm(struct mychip *chip) |
| { |
| struct snd_pcm *pcm; |
| .... |
| /* allocate your own data */ |
| chip->my_private_pcm_data = kmalloc(...); |
| /* set the destructor */ |
| pcm->private_data = chip; |
| pcm->private_free = mychip_pcm_free; |
| .... |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </section> |
| |
| <section id="pcm-interface-runtime"> |
| <title>Runtime Pointer - The Chest of PCM Information</title> |
| <para> |
| When the PCM substream is opened, a PCM runtime instance is |
| allocated and assigned to the substream. This pointer is |
| accessible via <constant>substream->runtime</constant>. |
| This runtime pointer holds the various information; it holds |
| the copy of hw_params and sw_params configurations, the buffer |
| pointers, mmap records, spinlocks, etc. Almost everyhing you |
| need for controlling the PCM can be found there. |
| </para> |
| |
| <para> |
| The definition of runtime instance is found in |
| <filename><sound/pcm.h></filename>. Here is the |
| copy from the file. |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct _snd_pcm_runtime { |
| /* -- Status -- */ |
| struct snd_pcm_substream *trigger_master; |
| snd_timestamp_t trigger_tstamp; /* trigger timestamp */ |
| int overrange; |
| snd_pcm_uframes_t avail_max; |
| snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */ |
| snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/ |
| |
| /* -- HW params -- */ |
| snd_pcm_access_t access; /* access mode */ |
| snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */ |
| snd_pcm_subformat_t subformat; /* subformat */ |
| unsigned int rate; /* rate in Hz */ |
| unsigned int channels; /* channels */ |
| snd_pcm_uframes_t period_size; /* period size */ |
| unsigned int periods; /* periods */ |
| snd_pcm_uframes_t buffer_size; /* buffer size */ |
| unsigned int tick_time; /* tick time */ |
| snd_pcm_uframes_t min_align; /* Min alignment for the format */ |
| size_t byte_align; |
| unsigned int frame_bits; |
| unsigned int sample_bits; |
| unsigned int info; |
| unsigned int rate_num; |
| unsigned int rate_den; |
| |
| /* -- SW params -- */ |
| struct timespec tstamp_mode; /* mmap timestamp is updated */ |
| unsigned int period_step; |
| unsigned int sleep_min; /* min ticks to sleep */ |
| snd_pcm_uframes_t xfer_align; /* xfer size need to be a multiple */ |
| snd_pcm_uframes_t start_threshold; |
| snd_pcm_uframes_t stop_threshold; |
| snd_pcm_uframes_t silence_threshold; /* Silence filling happens when |
| noise is nearest than this */ |
| snd_pcm_uframes_t silence_size; /* Silence filling size */ |
| snd_pcm_uframes_t boundary; /* pointers wrap point */ |
| |
| snd_pcm_uframes_t silenced_start; |
| snd_pcm_uframes_t silenced_size; |
| |
| snd_pcm_sync_id_t sync; /* hardware synchronization ID */ |
| |
| /* -- mmap -- */ |
| volatile struct snd_pcm_mmap_status *status; |
| volatile struct snd_pcm_mmap_control *control; |
| atomic_t mmap_count; |
| |
| /* -- locking / scheduling -- */ |
| spinlock_t lock; |
| wait_queue_head_t sleep; |
| struct timer_list tick_timer; |
| struct fasync_struct *fasync; |
| |
| /* -- private section -- */ |
| void *private_data; |
| void (*private_free)(struct snd_pcm_runtime *runtime); |
| |
| /* -- hardware description -- */ |
| struct snd_pcm_hardware hw; |
| struct snd_pcm_hw_constraints hw_constraints; |
| |
| /* -- interrupt callbacks -- */ |
| void (*transfer_ack_begin)(struct snd_pcm_substream *substream); |
| void (*transfer_ack_end)(struct snd_pcm_substream *substream); |
| |
| /* -- timer -- */ |
| unsigned int timer_resolution; /* timer resolution */ |
| |
| /* -- DMA -- */ |
| unsigned char *dma_area; /* DMA area */ |
| dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */ |
| size_t dma_bytes; /* size of DMA area */ |
| |
| struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */ |
| |
| #if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE) |
| /* -- OSS things -- */ |
| struct snd_pcm_oss_runtime oss; |
| #endif |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| For the operators (callbacks) of each sound driver, most of |
| these records are supposed to be read-only. Only the PCM |
| middle-layer changes / updates these info. The exceptions are |
| the hardware description (hw), interrupt callbacks |
| (transfer_ack_xxx), DMA buffer information, and the private |
| data. Besides, if you use the standard buffer allocation |
| method via <function>snd_pcm_lib_malloc_pages()</function>, |
| you don't need to set the DMA buffer information by yourself. |
| </para> |
| |
| <para> |
| In the sections below, important records are explained. |
| </para> |
| |
| <section id="pcm-interface-runtime-hw"> |
| <title>Hardware Description</title> |
| <para> |
| The hardware descriptor (struct <structname>snd_pcm_hardware</structname>) |
| contains the definitions of the fundamental hardware |
| configuration. Above all, you'll need to define this in |
| <link linkend="pcm-interface-operators-open-callback"><citetitle> |
| the open callback</citetitle></link>. |
| Note that the runtime instance holds the copy of the |
| descriptor, not the pointer to the existing descriptor. That |
| is, in the open callback, you can modify the copied descriptor |
| (<constant>runtime->hw</constant>) as you need. For example, if the maximum |
| number of channels is 1 only on some chip models, you can |
| still use the same hardware descriptor and change the |
| channels_max later: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_pcm_runtime *runtime = substream->runtime; |
| ... |
| runtime->hw = snd_mychip_playback_hw; /* common definition */ |
| if (chip->model == VERY_OLD_ONE) |
| runtime->hw.channels_max = 1; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Typically, you'll have a hardware descriptor like below: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct snd_pcm_hardware snd_mychip_playback_hw = { |
| .info = (SNDRV_PCM_INFO_MMAP | |
| SNDRV_PCM_INFO_INTERLEAVED | |
| SNDRV_PCM_INFO_BLOCK_TRANSFER | |
| SNDRV_PCM_INFO_MMAP_VALID), |
| .formats = SNDRV_PCM_FMTBIT_S16_LE, |
| .rates = SNDRV_PCM_RATE_8000_48000, |
| .rate_min = 8000, |
| .rate_max = 48000, |
| .channels_min = 2, |
| .channels_max = 2, |
| .buffer_bytes_max = 32768, |
| .period_bytes_min = 4096, |
| .period_bytes_max = 32768, |
| .periods_min = 1, |
| .periods_max = 1024, |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| <itemizedlist> |
| <listitem><para> |
| The <structfield>info</structfield> field contains the type and |
| capabilities of this pcm. The bit flags are defined in |
| <filename><sound/asound.h></filename> as |
| <constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you |
| have to specify whether the mmap is supported and which |
| interleaved format is supported. |
| When the mmap is supported, add |
| <constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the |
| hardware supports the interleaved or the non-interleaved |
| format, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or |
| <constant>SNDRV_PCM_INFO_NONINTERLEAVED</constant> flag must |
| be set, respectively. If both are supported, you can set both, |
| too. |
| </para> |
| |
| <para> |
| In the above example, <constant>MMAP_VALID</constant> and |
| <constant>BLOCK_TRANSFER</constant> are specified for OSS mmap |
| mode. Usually both are set. Of course, |
| <constant>MMAP_VALID</constant> is set only if the mmap is |
| really supported. |
| </para> |
| |
| <para> |
| The other possible flags are |
| <constant>SNDRV_PCM_INFO_PAUSE</constant> and |
| <constant>SNDRV_PCM_INFO_RESUME</constant>. The |
| <constant>PAUSE</constant> bit means that the pcm supports the |
| <quote>pause</quote> operation, while the |
| <constant>RESUME</constant> bit means that the pcm supports |
| the <quote>suspend/resume</quote> operation. If these flags |
| are set, the <structfield>trigger</structfield> callback below |
| must handle the corresponding commands. |
| </para> |
| |
| <para> |
| When the PCM substreams can be synchronized (typically, |
| synchorinized start/stop of a playback and a capture streams), |
| you can give <constant>SNDRV_PCM_INFO_SYNC_START</constant>, |
| too. In this case, you'll need to check the linked-list of |
| PCM substreams in the trigger callback. This will be |
| described in the later section. |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| <structfield>formats</structfield> field contains the bit-flags |
| of supported formats (<constant>SNDRV_PCM_FMTBIT_XXX</constant>). |
| If the hardware supports more than one format, give all or'ed |
| bits. In the example above, the signed 16bit little-endian |
| format is specified. |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| <structfield>rates</structfield> field contains the bit-flags of |
| supported rates (<constant>SNDRV_PCM_RATE_XXX</constant>). |
| When the chip supports continuous rates, pass |
| <constant>CONTINUOUS</constant> bit additionally. |
| The pre-defined rate bits are provided only for typical |
| rates. If your chip supports unconventional rates, you need to add |
| <constant>KNOT</constant> bit and set up the hardware |
| constraint manually (explained later). |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| <structfield>rate_min</structfield> and |
| <structfield>rate_max</structfield> define the minimal and |
| maximal sample rate. This should correspond somehow to |
| <structfield>rates</structfield> bits. |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| <structfield>channel_min</structfield> and |
| <structfield>channel_max</structfield> |
| define, as you might already expected, the minimal and maximal |
| number of channels. |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| <structfield>buffer_bytes_max</structfield> defines the |
| maximal buffer size in bytes. There is no |
| <structfield>buffer_bytes_min</structfield> field, since |
| it can be calculated from the minimal period size and the |
| minimal number of periods. |
| Meanwhile, <structfield>period_bytes_min</structfield> and |
| define the minimal and maximal size of the period in bytes. |
| <structfield>periods_max</structfield> and |
| <structfield>periods_min</structfield> define the maximal and |
| minimal number of periods in the buffer. |
| </para> |
| |
| <para> |
| The <quote>period</quote> is a term, that corresponds to |
| fragment in the OSS world. The period defines the size at |
| which the PCM interrupt is generated. This size strongly |
| depends on the hardware. |
| Generally, the smaller period size will give you more |
| interrupts, that is, more controls. |
| In the case of capture, this size defines the input latency. |
| On the other hand, the whole buffer size defines the |
| output latency for the playback direction. |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| There is also a field <structfield>fifo_size</structfield>. |
| This specifies the size of the hardware FIFO, but it's not |
| used currently in the driver nor in the alsa-lib. So, you |
| can ignore this field. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id="pcm-interface-runtime-config"> |
| <title>PCM Configurations</title> |
| <para> |
| Ok, let's go back again to the PCM runtime records. |
| The most frequently referred records in the runtime instance are |
| the PCM configurations. |
| The PCM configurations are stored on runtime instance |
| after the application sends <type>hw_params</type> data via |
| alsa-lib. There are many fields copied from hw_params and |
| sw_params structs. For example, |
| <structfield>format</structfield> holds the format type |
| chosen by the application. This field contains the enum value |
| <constant>SNDRV_PCM_FORMAT_XXX</constant>. |
| </para> |
| |
| <para> |
| One thing to be noted is that the configured buffer and period |
| sizes are stored in <quote>frames</quote> in the runtime |
| In the ALSA world, 1 frame = channels * samples-size. |
| For conversion between frames and bytes, you can use the |
| helper functions, <function>frames_to_bytes()</function> and |
| <function>bytes_to_frames()</function>. |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| period_bytes = frames_to_bytes(runtime, runtime->period_size); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Also, many software parameters (sw_params) are |
| stored in frames, too. Please check the type of the field. |
| <type>snd_pcm_uframes_t</type> is for the frames as unsigned |
| integer while <type>snd_pcm_sframes_t</type> is for the frames |
| as signed integer. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-runtime-dma"> |
| <title>DMA Buffer Information</title> |
| <para> |
| The DMA buffer is defined by the following four fields, |
| <structfield>dma_area</structfield>, |
| <structfield>dma_addr</structfield>, |
| <structfield>dma_bytes</structfield> and |
| <structfield>dma_private</structfield>. |
| The <structfield>dma_area</structfield> holds the buffer |
| pointer (the logical address). You can call |
| <function>memcpy</function> from/to |
| this pointer. Meanwhile, <structfield>dma_addr</structfield> |
| holds the physical address of the buffer. This field is |
| specified only when the buffer is a linear buffer. |
| <structfield>dma_bytes</structfield> holds the size of buffer |
| in bytes. <structfield>dma_private</structfield> is used for |
| the ALSA DMA allocator. |
| </para> |
| |
| <para> |
| If you use a standard ALSA function, |
| <function>snd_pcm_lib_malloc_pages()</function>, for |
| allocating the buffer, these fields are set by the ALSA middle |
| layer, and you should <emphasis>not</emphasis> change them by |
| yourself. You can read them but not write them. |
| On the other hand, if you want to allocate the buffer by |
| yourself, you'll need to manage it in hw_params callback. |
| At least, <structfield>dma_bytes</structfield> is mandatory. |
| <structfield>dma_area</structfield> is necessary when the |
| buffer is mmapped. If your driver doesn't support mmap, this |
| field is not necessary. <structfield>dma_addr</structfield> |
| is also not mandatory. You can use |
| <structfield>dma_private</structfield> as you like, too. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-runtime-status"> |
| <title>Running Status</title> |
| <para> |
| The running status can be referred via <constant>runtime->status</constant>. |
| This is the pointer to struct <structname>snd_pcm_mmap_status</structname> |
| record. For example, you can get the current DMA hardware |
| pointer via <constant>runtime->status->hw_ptr</constant>. |
| </para> |
| |
| <para> |
| The DMA application pointer can be referred via |
| <constant>runtime->control</constant>, which points |
| struct <structname>snd_pcm_mmap_control</structname> record. |
| However, accessing directly to this value is not recommended. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-runtime-private"> |
| <title>Private Data</title> |
| <para> |
| You can allocate a record for the substream and store it in |
| <constant>runtime->private_data</constant>. Usually, this |
| done in |
| <link linkend="pcm-interface-operators-open-callback"><citetitle> |
| the open callback</citetitle></link>. |
| Don't mix this with <constant>pcm->private_data</constant>. |
| The <constant>pcm->private_data</constant> usually points the |
| chip instance assigned statically at the creation of PCM, while the |
| <constant>runtime->private_data</constant> points a dynamic |
| data created at the PCM open callback. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_open(struct snd_pcm_substream *substream) |
| { |
| struct my_pcm_data *data; |
| .... |
| data = kmalloc(sizeof(*data), GFP_KERNEL); |
| substream->runtime->private_data = data; |
| .... |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The allocated object must be released in |
| <link linkend="pcm-interface-operators-open-callback"><citetitle> |
| the close callback</citetitle></link>. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-runtime-intr"> |
| <title>Interrupt Callbacks</title> |
| <para> |
| The field <structfield>transfer_ack_begin</structfield> and |
| <structfield>transfer_ack_end</structfield> are called at |
| the beginning and the end of |
| <function>snd_pcm_period_elapsed()</function>, respectively. |
| </para> |
| </section> |
| |
| </section> |
| |
| <section id="pcm-interface-operators"> |
| <title>Operators</title> |
| <para> |
| OK, now let me explain the detail of each pcm callback |
| (<parameter>ops</parameter>). In general, every callback must |
| return 0 if successful, or a negative number with the error |
| number such as <constant>-EINVAL</constant> at any |
| error. |
| </para> |
| |
| <para> |
| The callback function takes at least the argument with |
| <structname>snd_pcm_substream</structname> pointer. For retrieving the |
| chip record from the given substream instance, you can use the |
| following macro. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| int xxx() { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| .... |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| The macro reads <constant>substream->private_data</constant>, |
| which is a copy of <constant>pcm->private_data</constant>. |
| You can override the former if you need to assign different data |
| records per PCM substream. For example, cmi8330 driver assigns |
| different private_data for playback and capture directions, |
| because it uses two different codecs (SB- and AD-compatible) for |
| different directions. |
| </para> |
| |
| <section id="pcm-interface-operators-open-callback"> |
| <title>open callback</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_open(struct snd_pcm_substream *substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| This is called when a pcm substream is opened. |
| </para> |
| |
| <para> |
| At least, here you have to initialize the runtime->hw |
| record. Typically, this is done by like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_open(struct snd_pcm_substream *substream) |
| { |
| struct mychip *chip = snd_pcm_substream_chip(substream); |
| struct snd_pcm_runtime *runtime = substream->runtime; |
| |
| runtime->hw = snd_mychip_playback_hw; |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where <parameter>snd_mychip_playback_hw</parameter> is the |
| pre-defined hardware description. |
| </para> |
| |
| <para> |
| You can allocate a private data in this callback, as described |
| in <link linkend="pcm-interface-runtime-private"><citetitle> |
| Private Data</citetitle></link> section. |
| </para> |
| |
| <para> |
| If the hardware configuration needs more constraints, set the |
| hardware constraints here, too. |
| See <link linkend="pcm-interface-constraints"><citetitle> |
| Constraints</citetitle></link> for more details. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-close-callback"> |
| <title>close callback</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_close(struct snd_pcm_substream *substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| Obviously, this is called when a pcm substream is closed. |
| </para> |
| |
| <para> |
| Any private instance for a pcm substream allocated in the |
| open callback will be released here. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_close(struct snd_pcm_substream *substream) |
| { |
| .... |
| kfree(substream->runtime->private_data); |
| .... |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-ioctl-callback"> |
| <title>ioctl callback</title> |
| <para> |
| This is used for any special action to pcm ioctls. But |
| usually you can pass a generic ioctl callback, |
| <function>snd_pcm_lib_ioctl</function>. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-hw-params-callback"> |
| <title>hw_params callback</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_hw_params(struct snd_pcm_substream *substream, |
| struct snd_pcm_hw_params *hw_params); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| This and <structfield>hw_free</structfield> callbacks exist |
| only on ALSA 0.9.x. |
| </para> |
| |
| <para> |
| This is called when the hardware parameter |
| (<structfield>hw_params</structfield>) is set |
| up by the application, |
| that is, once when the buffer size, the period size, the |
| format, etc. are defined for the pcm substream. |
| </para> |
| |
| <para> |
| Many hardware set-up should be done in this callback, |
| including the allocation of buffers. |
| </para> |
| |
| <para> |
| Parameters to be initialized are retrieved by |
| <function>params_xxx()</function> macros. For allocating a |
| buffer, you can call a helper function, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params)); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| <function>snd_pcm_lib_malloc_pages()</function> is available |
| only when the DMA buffers have been pre-allocated. |
| See the section <link |
| linkend="buffer-and-memory-buffer-types"><citetitle> |
| Buffer Types</citetitle></link> for more details. |
| </para> |
| |
| <para> |
| Note that this and <structfield>prepare</structfield> callbacks |
| may be called multiple times per initialization. |
| For example, the OSS emulation may |
| call these callbacks at each change via its ioctl. |
| </para> |
| |
| <para> |
| Thus, you need to take care not to allocate the same buffers |
| many times, which will lead to memory leak! Calling the |
| helper function above many times is OK. It will release the |
| previous buffer automatically when it was already allocated. |
| </para> |
| |
| <para> |
| Another note is that this callback is non-atomic |
| (schedulable). This is important, because the |
| <structfield>trigger</structfield> callback |
| is atomic (non-schedulable). That is, mutex or any |
| schedule-related functions are not available in |
| <structfield>trigger</structfield> callback. |
| Please see the subsection |
| <link linkend="pcm-interface-atomicity"><citetitle> |
| Atomicity</citetitle></link> for details. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-hw-free-callback"> |
| <title>hw_free callback</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_hw_free(struct snd_pcm_substream *substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| This is called to release the resources allocated via |
| <structfield>hw_params</structfield>. For example, releasing the |
| buffer via |
| <function>snd_pcm_lib_malloc_pages()</function> is done by |
| calling the following: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_lib_free_pages(substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| This function is always called before the close callback is called. |
| Also, the callback may be called multiple times, too. |
| Keep track whether the resource was already released. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-prepare-callback"> |
| <title>prepare callback</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_prepare(struct snd_pcm_substream *substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| This callback is called when the pcm is |
| <quote>prepared</quote>. You can set the format type, sample |
| rate, etc. here. The difference from |
| <structfield>hw_params</structfield> is that the |
| <structfield>prepare</structfield> callback will be called at each |
| time |
| <function>snd_pcm_prepare()</function> is called, i.e. when |
| recovered after underruns, etc. |
| </para> |
| |
| <para> |
| Note that this callback became non-atomic since the recent version. |
| You can use schedule-related fucntions safely in this callback now. |
| </para> |
| |
| <para> |
| In this and the following callbacks, you can refer to the |
| values via the runtime record, |
| substream->runtime. |
| For example, to get the current |
| rate, format or channels, access to |
| runtime->rate, |
| runtime->format or |
| runtime->channels, respectively. |
| The physical address of the allocated buffer is set to |
| runtime->dma_area. The buffer and period sizes are |
| in runtime->buffer_size and runtime->period_size, |
| respectively. |
| </para> |
| |
| <para> |
| Be careful that this callback will be called many times at |
| each set up, too. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-trigger-callback"> |
| <title>trigger callback</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| This is called when the pcm is started, stopped or paused. |
| </para> |
| |
| <para> |
| Which action is specified in the second argument, |
| <constant>SNDRV_PCM_TRIGGER_XXX</constant> in |
| <filename><sound/pcm.h></filename>. At least, |
| <constant>START</constant> and <constant>STOP</constant> |
| commands must be defined in this callback. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| switch (cmd) { |
| case SNDRV_PCM_TRIGGER_START: |
| // do something to start the PCM engine |
| break; |
| case SNDRV_PCM_TRIGGER_STOP: |
| // do something to stop the PCM engine |
| break; |
| default: |
| return -EINVAL; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| When the pcm supports the pause operation (given in info |
| field of the hardware table), <constant>PAUSE_PUSE</constant> |
| and <constant>PAUSE_RELEASE</constant> commands must be |
| handled here, too. The former is the command to pause the pcm, |
| and the latter to restart the pcm again. |
| </para> |
| |
| <para> |
| When the pcm supports the suspend/resume operation |
| (i.e. <constant>SNDRV_PCM_INFO_RESUME</constant> flag is set), |
| <constant>SUSPEND</constant> and <constant>RESUME</constant> |
| commands must be handled, too. |
| These commands are issued when the power-management status is |
| changed. Obviously, the <constant>SUSPEND</constant> and |
| <constant>RESUME</constant> |
| do suspend and resume of the pcm substream, and usually, they |
| are identical with <constant>STOP</constant> and |
| <constant>START</constant> commands, respectively. |
| </para> |
| |
| <para> |
| As mentioned, this callback is atomic. You cannot call |
| the function going to sleep. |
| The trigger callback should be as minimal as possible, |
| just really triggering the DMA. The other stuff should be |
| initialized hw_params and prepare callbacks properly |
| beforehand. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-pointer-callback"> |
| <title>pointer callback</title> |
| <para> |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream) |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| This callback is called when the PCM middle layer inquires |
| the current hardware position on the buffer. The position must |
| be returned in frames (which was in bytes on ALSA 0.5.x), |
| ranged from 0 to buffer_size - 1. |
| </para> |
| |
| <para> |
| This is called usually from the buffer-update routine in the |
| pcm middle layer, which is invoked when |
| <function>snd_pcm_period_elapsed()</function> is called in the |
| interrupt routine. Then the pcm middle layer updates the |
| position and calculates the available space, and wakes up the |
| sleeping poll threads, etc. |
| </para> |
| |
| <para> |
| This callback is also atomic. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-copy-silence"> |
| <title>copy and silence callbacks</title> |
| <para> |
| These callbacks are not mandatory, and can be omitted in |
| most cases. These callbacks are used when the hardware buffer |
| cannot be on the normal memory space. Some chips have their |
| own buffer on the hardware which is not mappable. In such a |
| case, you have to transfer the data manually from the memory |
| buffer to the hardware buffer. Or, if the buffer is |
| non-contiguous on both physical and virtual memory spaces, |
| these callbacks must be defined, too. |
| </para> |
| |
| <para> |
| If these two callbacks are defined, copy and set-silence |
| operations are done by them. The detailed will be described in |
| the later section <link |
| linkend="buffer-and-memory"><citetitle>Buffer and Memory |
| Management</citetitle></link>. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-ack"> |
| <title>ack callback</title> |
| <para> |
| This callback is also not mandatory. This callback is called |
| when the appl_ptr is updated in read or write operations. |
| Some drivers like emu10k1-fx and cs46xx need to track the |
| current appl_ptr for the internal buffer, and this callback |
| is useful only for such a purpose. |
| </para> |
| <para> |
| This callback is atomic. |
| </para> |
| </section> |
| |
| <section id="pcm-interface-operators-page-callback"> |
| <title>page callback</title> |
| |
| <para> |
| This callback is also not mandatory. This callback is used |
| mainly for the non-contiguous buffer. The mmap calls this |
| callback to get the page address. Some examples will be |
| explained in the later section <link |
| linkend="buffer-and-memory"><citetitle>Buffer and Memory |
| Management</citetitle></link>, too. |
| </para> |
| </section> |
| </section> |
| |
| <section id="pcm-interface-interrupt-handler"> |
| <title>Interrupt Handler</title> |
| <para> |
| The rest of pcm stuff is the PCM interrupt handler. The |
| role of PCM interrupt handler in the sound driver is to update |
| the buffer position and to tell the PCM middle layer when the |
| buffer position goes across the prescribed period size. To |
| inform this, call <function>snd_pcm_period_elapsed()</function> |
| function. |
| </para> |
| |
| <para> |
| There are several types of sound chips to generate the interrupts. |
| </para> |
| |
| <section id="pcm-interface-interrupt-handler-boundary"> |
| <title>Interrupts at the period (fragment) boundary</title> |
| <para> |
| This is the most frequently found type: the hardware |
| generates an interrupt at each period boundary. |
| In this case, you can call |
| <function>snd_pcm_period_elapsed()</function> at each |
| interrupt. |
| </para> |
| |
| <para> |
| <function>snd_pcm_period_elapsed()</function> takes the |
| substream pointer as its argument. Thus, you need to keep the |
| substream pointer accessible from the chip instance. For |
| example, define substream field in the chip record to hold the |
| current running substream pointer, and set the pointer value |
| at open callback (and reset at close callback). |
| </para> |
| |
| <para> |
| If you aquire a spinlock in the interrupt handler, and the |
| lock is used in other pcm callbacks, too, then you have to |
| release the lock before calling |
| <function>snd_pcm_period_elapsed()</function>, because |
| <function>snd_pcm_period_elapsed()</function> calls other pcm |
| callbacks inside. |
| </para> |
| |
| <para> |
| A typical coding would be like: |
| |
| <example> |
| <title>Interrupt Handler Case #1</title> |
| <programlisting> |
| <![CDATA[ |
| static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id, |
| struct pt_regs *regs) |
| { |
| struct mychip *chip = dev_id; |
| spin_lock(&chip->lock); |
| .... |
| if (pcm_irq_invoked(chip)) { |
| /* call updater, unlock before it */ |
| spin_unlock(&chip->lock); |
| snd_pcm_period_elapsed(chip->substream); |
| spin_lock(&chip->lock); |
| // acknowledge the interrupt if necessary |
| } |
| .... |
| spin_unlock(&chip->lock); |
| return IRQ_HANDLED; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </section> |
| |
| <section id="pcm-interface-interrupt-handler-timer"> |
| <title>High-frequent timer interrupts</title> |
| <para> |
| This is the case when the hardware doesn't generate interrupts |
| at the period boundary but do timer-interrupts at the fixed |
| timer rate (e.g. es1968 or ymfpci drivers). |
| In this case, you need to check the current hardware |
| position and accumulates the processed sample length at each |
| interrupt. When the accumulated size overcomes the period |
| size, call |
| <function>snd_pcm_period_elapsed()</function> and reset the |
| accumulator. |
| </para> |
| |
| <para> |
| A typical coding would be like the following. |
| |
| <example> |
| <title>Interrupt Handler Case #2</title> |
| <programlisting> |
| <![CDATA[ |
| static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id, |
| struct pt_regs *regs) |
| { |
| struct mychip *chip = dev_id; |
| spin_lock(&chip->lock); |
| .... |
| if (pcm_irq_invoked(chip)) { |
| unsigned int last_ptr, size; |
| /* get the current hardware pointer (in frames) */ |
| last_ptr = get_hw_ptr(chip); |
| /* calculate the processed frames since the |
| * last update |
| */ |
| if (last_ptr < chip->last_ptr) |
| size = runtime->buffer_size + last_ptr |
| - chip->last_ptr; |
| else |
| size = last_ptr - chip->last_ptr; |
| /* remember the last updated point */ |
| chip->last_ptr = last_ptr; |
| /* accumulate the size */ |
| chip->size += size; |
| /* over the period boundary? */ |
| if (chip->size >= runtime->period_size) { |
| /* reset the accumulator */ |
| chip->size %= runtime->period_size; |
| /* call updater */ |
| spin_unlock(&chip->lock); |
| snd_pcm_period_elapsed(substream); |
| spin_lock(&chip->lock); |
| } |
| // acknowledge the interrupt if necessary |
| } |
| .... |
| spin_unlock(&chip->lock); |
| return IRQ_HANDLED; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </section> |
| |
| <section id="pcm-interface-interrupt-handler-both"> |
| <title>On calling <function>snd_pcm_period_elapsed()</function></title> |
| <para> |
| In both cases, even if more than one period are elapsed, you |
| don't have to call |
| <function>snd_pcm_period_elapsed()</function> many times. Call |
| only once. And the pcm layer will check the current hardware |
| pointer and update to the latest status. |
| </para> |
| </section> |
| </section> |
| |
| <section id="pcm-interface-atomicity"> |
| <title>Atomicity</title> |
| <para> |
| One of the most important (and thus difficult to debug) problem |
| on the kernel programming is the race condition. |
| On linux kernel, usually it's solved via spin-locks or |
| semaphores. In general, if the race condition may |
| happen in the interrupt handler, it's handled as atomic, and you |
| have to use spinlock for protecting the critical session. If it |
| never happens in the interrupt and it may take relatively long |
| time, you should use semaphore. |
| </para> |
| |
| <para> |
| As already seen, some pcm callbacks are atomic and some are |
| not. For example, <parameter>hw_params</parameter> callback is |
| non-atomic, while <parameter>trigger</parameter> callback is |
| atomic. This means, the latter is called already in a spinlock |
| held by the PCM middle layer. Please take this atomicity into |
| account when you use a spinlock or a semaphore in the callbacks. |
| </para> |
| |
| <para> |
| In the atomic callbacks, you cannot use functions which may call |
| <function>schedule</function> or go to |
| <function>sleep</function>. The semaphore and mutex do sleep, |
| and hence they cannot be used inside the atomic callbacks |
| (e.g. <parameter>trigger</parameter> callback). |
| For taking a certain delay in such a callback, please use |
| <function>udelay()</function> or <function>mdelay()</function>. |
| </para> |
| |
| <para> |
| All three atomic callbacks (trigger, pointer, and ack) are |
| called with local interrupts disabled. |
| </para> |
| |
| </section> |
| <section id="pcm-interface-constraints"> |
| <title>Constraints</title> |
| <para> |
| If your chip supports unconventional sample rates, or only the |
| limited samples, you need to set a constraint for the |
| condition. |
| </para> |
| |
| <para> |
| For example, in order to restrict the sample rates in the some |
| supported values, use |
| <function>snd_pcm_hw_constraint_list()</function>. |
| You need to call this function in the open callback. |
| |
| <example> |
| <title>Example of Hardware Constraints</title> |
| <programlisting> |
| <![CDATA[ |
| static unsigned int rates[] = |
| {4000, 10000, 22050, 44100}; |
| static struct snd_pcm_hw_constraint_list constraints_rates = { |
| .count = ARRAY_SIZE(rates), |
| .list = rates, |
| .mask = 0, |
| }; |
| |
| static int snd_mychip_pcm_open(struct snd_pcm_substream *substream) |
| { |
| int err; |
| .... |
| err = snd_pcm_hw_constraint_list(substream->runtime, 0, |
| SNDRV_PCM_HW_PARAM_RATE, |
| &constraints_rates); |
| if (err < 0) |
| return err; |
| .... |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| |
| <para> |
| There are many different constraints. |
| Look in <filename>sound/pcm.h</filename> for a complete list. |
| You can even define your own constraint rules. |
| For example, let's suppose my_chip can manage a substream of 1 channel |
| if and only if the format is S16_LE, otherwise it supports any format |
| specified in the <structname>snd_pcm_hardware</structname> stucture (or in any |
| other constraint_list). You can build a rule like this: |
| |
| <example> |
| <title>Example of Hardware Constraints for Channels</title> |
| <programlisting> |
| <![CDATA[ |
| static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params, |
| struct snd_pcm_hw_rule *rule) |
| { |
| struct snd_interval *c = hw_param_interval(params, |
| SNDRV_PCM_HW_PARAM_CHANNELS); |
| struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); |
| struct snd_mask fmt; |
| |
| snd_mask_any(&fmt); /* Init the struct */ |
| if (c->min < 2) { |
| fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; |
| return snd_mask_refine(f, &fmt); |
| } |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| |
| <para> |
| Then you need to call this function to add your rule: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, |
| hw_rule_channels_by_format, 0, SNDRV_PCM_HW_PARAM_FORMAT, |
| -1); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The rule function is called when an application sets the number of |
| channels. But an application can set the format before the number of |
| channels. Thus you also need to define the inverse rule: |
| |
| <example> |
| <title>Example of Hardware Constraints for Channels</title> |
| <programlisting> |
| <![CDATA[ |
| static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params, |
| struct snd_pcm_hw_rule *rule) |
| { |
| struct snd_interval *c = hw_param_interval(params, |
| SNDRV_PCM_HW_PARAM_CHANNELS); |
| struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); |
| struct snd_interval ch; |
| |
| snd_interval_any(&ch); |
| if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { |
| ch.min = ch.max = 1; |
| ch.integer = 1; |
| return snd_interval_refine(c, &ch); |
| } |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| |
| <para> |
| ...and in the open callback: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, |
| hw_rule_format_by_channels, 0, SNDRV_PCM_HW_PARAM_CHANNELS, |
| -1); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| I won't explain more details here, rather I |
| would like to say, <quote>Luke, use the source.</quote> |
| </para> |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Control Interface --> |
| <!-- ****************************************************** --> |
| <chapter id="control-interface"> |
| <title>Control Interface</title> |
| |
| <section id="control-interface-general"> |
| <title>General</title> |
| <para> |
| The control interface is used widely for many switches, |
| sliders, etc. which are accessed from the user-space. Its most |
| important use is the mixer interface. In other words, on ALSA |
| 0.9.x, all the mixer stuff is implemented on the control kernel |
| API (while there was an independent mixer kernel API on 0.5.x). |
| </para> |
| |
| <para> |
| ALSA has a well-defined AC97 control module. If your chip |
| supports only the AC97 and nothing else, you can skip this |
| section. |
| </para> |
| |
| <para> |
| The control API is defined in |
| <filename><sound/control.h></filename>. |
| Include this file if you add your own controls. |
| </para> |
| </section> |
| |
| <section id="control-interface-definition"> |
| <title>Definition of Controls</title> |
| <para> |
| For creating a new control, you need to define the three |
| callbacks: <structfield>info</structfield>, |
| <structfield>get</structfield> and |
| <structfield>put</structfield>. Then, define a |
| struct <structname>snd_kcontrol_new</structname> record, such as: |
| |
| <example> |
| <title>Definition of a Control</title> |
| <programlisting> |
| <![CDATA[ |
| static struct snd_kcontrol_new my_control __devinitdata = { |
| .iface = SNDRV_CTL_ELEM_IFACE_MIXER, |
| .name = "PCM Playback Switch", |
| .index = 0, |
| .access = SNDRV_CTL_ELEM_ACCESS_READWRITE, |
| .private_values = 0xffff, |
| .info = my_control_info, |
| .get = my_control_get, |
| .put = my_control_put |
| }; |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| |
| <para> |
| Most likely the control is created via |
| <function>snd_ctl_new1()</function>, and in such a case, you can |
| add <parameter>__devinitdata</parameter> prefix to the |
| definition like above. |
| </para> |
| |
| <para> |
| The <structfield>iface</structfield> field specifies the type of |
| the control, <constant>SNDRV_CTL_ELEM_IFACE_XXX</constant>, which |
| is usually <constant>MIXER</constant>. |
| Use <constant>CARD</constant> for global controls that are not |
| logically part of the mixer. |
| If the control is closely associated with some specific device on |
| the sound card, use <constant>HWDEP</constant>, |
| <constant>PCM</constant>, <constant>RAWMIDI</constant>, |
| <constant>TIMER</constant>, or <constant>SEQUENCER</constant>, and |
| specify the device number with the |
| <structfield>device</structfield> and |
| <structfield>subdevice</structfield> fields. |
| </para> |
| |
| <para> |
| The <structfield>name</structfield> is the name identifier |
| string. On ALSA 0.9.x, the control name is very important, |
| because its role is classified from its name. There are |
| pre-defined standard control names. The details are described in |
| the subsection |
| <link linkend="control-interface-control-names"><citetitle> |
| Control Names</citetitle></link>. |
| </para> |
| |
| <para> |
| The <structfield>index</structfield> field holds the index number |
| of this control. If there are several different controls with |
| the same name, they can be distinguished by the index |
| number. This is the case when |
| several codecs exist on the card. If the index is zero, you can |
| omit the definition above. |
| </para> |
| |
| <para> |
| The <structfield>access</structfield> field contains the access |
| type of this control. Give the combination of bit masks, |
| <constant>SNDRV_CTL_ELEM_ACCESS_XXX</constant>, there. |
| The detailed will be explained in the subsection |
| <link linkend="control-interface-access-flags"><citetitle> |
| Access Flags</citetitle></link>. |
| </para> |
| |
| <para> |
| The <structfield>private_values</structfield> field contains |
| an arbitrary long integer value for this record. When using |
| generic <structfield>info</structfield>, |
| <structfield>get</structfield> and |
| <structfield>put</structfield> callbacks, you can pass a value |
| through this field. If several small numbers are necessary, you can |
| combine them in bitwise. Or, it's possible to give a pointer |
| (casted to unsigned long) of some record to this field, too. |
| </para> |
| |
| <para> |
| The other three are |
| <link linkend="control-interface-callbacks"><citetitle> |
| callback functions</citetitle></link>. |
| </para> |
| </section> |
| |
| <section id="control-interface-control-names"> |
| <title>Control Names</title> |
| <para> |
| There are some standards for defining the control names. A |
| control is usually defined from the three parts as |
| <quote>SOURCE DIRECTION FUNCTION</quote>. |
| </para> |
| |
| <para> |
| The first, <constant>SOURCE</constant>, specifies the source |
| of the control, and is a string such as <quote>Master</quote>, |
| <quote>PCM</quote>, <quote>CD</quote> or |
| <quote>Line</quote>. There are many pre-defined sources. |
| </para> |
| |
| <para> |
| The second, <constant>DIRECTION</constant>, is one of the |
| following strings according to the direction of the control: |
| <quote>Playback</quote>, <quote>Capture</quote>, <quote>Bypass |
| Playback</quote> and <quote>Bypass Capture</quote>. Or, it can |
| be omitted, meaning both playback and capture directions. |
| </para> |
| |
| <para> |
| The third, <constant>FUNCTION</constant>, is one of the |
| following strings according to the function of the control: |
| <quote>Switch</quote>, <quote>Volume</quote> and |
| <quote>Route</quote>. |
| </para> |
| |
| <para> |
| The example of control names are, thus, <quote>Master Capture |
| Switch</quote> or <quote>PCM Playback Volume</quote>. |
| </para> |
| |
| <para> |
| There are some exceptions: |
| </para> |
| |
| <section id="control-interface-control-names-global"> |
| <title>Global capture and playback</title> |
| <para> |
| <quote>Capture Source</quote>, <quote>Capture Switch</quote> |
| and <quote>Capture Volume</quote> are used for the global |
| capture (input) source, switch and volume. Similarly, |
| <quote>Playback Switch</quote> and <quote>Playback |
| Volume</quote> are used for the global output gain switch and |
| volume. |
| </para> |
| </section> |
| |
| <section id="control-interface-control-names-tone"> |
| <title>Tone-controls</title> |
| <para> |
| tone-control switch and volumes are specified like |
| <quote>Tone Control - XXX</quote>, e.g. <quote>Tone Control - |
| Switch</quote>, <quote>Tone Control - Bass</quote>, |
| <quote>Tone Control - Center</quote>. |
| </para> |
| </section> |
| |
| <section id="control-interface-control-names-3d"> |
| <title>3D controls</title> |
| <para> |
| 3D-control switches and volumes are specified like <quote>3D |
| Control - XXX</quote>, e.g. <quote>3D Control - |
| Switch</quote>, <quote>3D Control - Center</quote>, <quote>3D |
| Control - Space</quote>. |
| </para> |
| </section> |
| |
| <section id="control-interface-control-names-mic"> |
| <title>Mic boost</title> |
| <para> |
| Mic-boost switch is set as <quote>Mic Boost</quote> or |
| <quote>Mic Boost (6dB)</quote>. |
| </para> |
| |
| <para> |
| More precise information can be found in |
| <filename>Documentation/sound/alsa/ControlNames.txt</filename>. |
| </para> |
| </section> |
| </section> |
| |
| <section id="control-interface-access-flags"> |
| <title>Access Flags</title> |
| |
| <para> |
| The access flag is the bit-flags which specifies the access type |
| of the given control. The default access type is |
| <constant>SNDRV_CTL_ELEM_ACCESS_READWRITE</constant>, |
| which means both read and write are allowed to this control. |
| When the access flag is omitted (i.e. = 0), it is |
| regarded as <constant>READWRITE</constant> access as default. |
| </para> |
| |
| <para> |
| When the control is read-only, pass |
| <constant>SNDRV_CTL_ELEM_ACCESS_READ</constant> instead. |
| In this case, you don't have to define |
| <structfield>put</structfield> callback. |
| Similarly, when the control is write-only (although it's a rare |
| case), you can use <constant>WRITE</constant> flag instead, and |
| you don't need <structfield>get</structfield> callback. |
| </para> |
| |
| <para> |
| If the control value changes frequently (e.g. the VU meter), |
| <constant>VOLATILE</constant> flag should be given. This means |
| that the control may be changed without |
| <link linkend="control-interface-change-notification"><citetitle> |
| notification</citetitle></link>. Applications should poll such |
| a control constantly. |
| </para> |
| |
| <para> |
| When the control is inactive, set |
| <constant>INACTIVE</constant> flag, too. |
| There are <constant>LOCK</constant> and |
| <constant>OWNER</constant> flags for changing the write |
| permissions. |
| </para> |
| |
| </section> |
| |
| <section id="control-interface-callbacks"> |
| <title>Callbacks</title> |
| |
| <section id="control-interface-callbacks-info"> |
| <title>info callback</title> |
| <para> |
| The <structfield>info</structfield> callback is used to get |
| the detailed information of this control. This must store the |
| values of the given struct <structname>snd_ctl_elem_info</structname> |
| object. For example, for a boolean control with a single |
| element will be: |
| |
| <example> |
| <title>Example of info callback</title> |
| <programlisting> |
| <![CDATA[ |
| static int snd_myctl_info(struct snd_kcontrol *kcontrol, |
| struct snd_ctl_elem_info *uinfo) |
| { |
| uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN; |
| uinfo->count = 1; |
| uinfo->value.integer.min = 0; |
| uinfo->value.integer.max = 1; |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| |
| <para> |
| The <structfield>type</structfield> field specifies the type |
| of the control. There are <constant>BOOLEAN</constant>, |
| <constant>INTEGER</constant>, <constant>ENUMERATED</constant>, |
| <constant>BYTES</constant>, <constant>IEC958</constant> and |
| <constant>INTEGER64</constant>. The |
| <structfield>count</structfield> field specifies the |
| number of elements in this control. For example, a stereo |
| volume would have count = 2. The |
| <structfield>value</structfield> field is a union, and |
| the values stored are depending on the type. The boolean and |
| integer are identical. |
| </para> |
| |
| <para> |
| The enumerated type is a bit different from others. You'll |
| need to set the string for the currently given item index. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_myctl_info(struct snd_kcontrol *kcontrol, |
| struct snd_ctl_elem_info *uinfo) |
| { |
| static char *texts[4] = { |
| "First", "Second", "Third", "Fourth" |
| }; |
| uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED; |
| uinfo->count = 1; |
| uinfo->value.enumerated.items = 4; |
| if (uinfo->value.enumerated.item > 3) |
| uinfo->value.enumerated.item = 3; |
| strcpy(uinfo->value.enumerated.name, |
| texts[uinfo->value.enumerated.item]); |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| <section id="control-interface-callbacks-get"> |
| <title>get callback</title> |
| |
| <para> |
| This callback is used to read the current value of the |
| control and to return to the user-space. |
| </para> |
| |
| <para> |
| For example, |
| |
| <example> |
| <title>Example of get callback</title> |
| <programlisting> |
| <![CDATA[ |
| static int snd_myctl_get(struct snd_kcontrol *kcontrol, |
| struct snd_ctl_elem_value *ucontrol) |
| { |
| struct mychip *chip = snd_kcontrol_chip(kcontrol); |
| ucontrol->value.integer.value[0] = get_some_value(chip); |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| |
| <para> |
| Here, the chip instance is retrieved via |
| <function>snd_kcontrol_chip()</function> macro. This macro |
| just accesses to kcontrol->private_data. The |
| kcontrol->private_data field is |
| given as the argument of <function>snd_ctl_new()</function> |
| (see the later subsection |
| <link linkend="control-interface-constructor"><citetitle>Constructor</citetitle></link>). |
| </para> |
| |
| <para> |
| The <structfield>value</structfield> field is depending on |
| the type of control as well as on info callback. For example, |
| the sb driver uses this field to store the register offset, |
| the bit-shift and the bit-mask. The |
| <structfield>private_value</structfield> is set like |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| .private_value = reg | (shift << 16) | (mask << 24) |
| ]]> |
| </programlisting> |
| </informalexample> |
| and is retrieved in callbacks like |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol, |
| struct snd_ctl_elem_value *ucontrol) |
| { |
| int reg = kcontrol->private_value & 0xff; |
| int shift = (kcontrol->private_value >> 16) & 0xff; |
| int mask = (kcontrol->private_value >> 24) & 0xff; |
| .... |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| In <structfield>get</structfield> callback, you have to fill all the elements if the |
| control has more than one elements, |
| i.e. <structfield>count</structfield> > 1. |
| In the example above, we filled only one element |
| (<structfield>value.integer.value[0]</structfield>) since it's |
| assumed as <structfield>count</structfield> = 1. |
| </para> |
| </section> |
| |
| <section id="control-interface-callbacks-put"> |
| <title>put callback</title> |
| |
| <para> |
| This callback is used to write a value from the user-space. |
| </para> |
| |
| <para> |
| For example, |
| |
| <example> |
| <title>Example of put callback</title> |
| <programlisting> |
| <![CDATA[ |
| static int snd_myctl_put(struct snd_kcontrol *kcontrol, |
| struct snd_ctl_elem_value *ucontrol) |
| { |
| struct mychip *chip = snd_kcontrol_chip(kcontrol); |
| int changed = 0; |
| if (chip->current_value != |
| ucontrol->value.integer.value[0]) { |
| change_current_value(chip, |
| ucontrol->value.integer.value[0]); |
| changed = 1; |
| } |
| return changed; |
| } |
| ]]> |
| </programlisting> |
| </example> |
| |
| As seen above, you have to return 1 if the value is |
| changed. If the value is not changed, return 0 instead. |
| If any fatal error happens, return a negative error code as |
| usual. |
| </para> |
| |
| <para> |
| Like <structfield>get</structfield> callback, |
| when the control has more than one elements, |
| all elemehts must be evaluated in this callback, too. |
| </para> |
| </section> |
| |
| <section id="control-interface-callbacks-all"> |
| <title>Callbacks are not atomic</title> |
| <para> |
| All these three callbacks are basically not atomic. |
| </para> |
| </section> |
| </section> |
| |
| <section id="control-interface-constructor"> |
| <title>Constructor</title> |
| <para> |
| When everything is ready, finally we can create a new |
| control. For creating a control, there are two functions to be |
| called, <function>snd_ctl_new1()</function> and |
| <function>snd_ctl_add()</function>. |
| </para> |
| |
| <para> |
| In the simplest way, you can do like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| if ((err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip))) < 0) |
| return err; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where <parameter>my_control</parameter> is the |
| struct <structname>snd_kcontrol_new</structname> object defined above, and chip |
| is the object pointer to be passed to |
| kcontrol->private_data |
| which can be referred in callbacks. |
| </para> |
| |
| <para> |
| <function>snd_ctl_new1()</function> allocates a new |
| <structname>snd_kcontrol</structname> instance (that's why the definition |
| of <parameter>my_control</parameter> can be with |
| <parameter>__devinitdata</parameter> |
| prefix), and <function>snd_ctl_add</function> assigns the given |
| control component to the card. |
| </para> |
| </section> |
| |
| <section id="control-interface-change-notification"> |
| <title>Change Notification</title> |
| <para> |
| If you need to change and update a control in the interrupt |
| routine, you can call <function>snd_ctl_notify()</function>. For |
| example, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| This function takes the card pointer, the event-mask, and the |
| control id pointer for the notification. The event-mask |
| specifies the types of notification, for example, in the above |
| example, the change of control values is notified. |
| The id pointer is the pointer of struct <structname>snd_ctl_elem_id</structname> |
| to be notified. |
| You can find some examples in <filename>es1938.c</filename> or |
| <filename>es1968.c</filename> for hardware volume interrupts. |
| </para> |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- API for AC97 Codec --> |
| <!-- ****************************************************** --> |
| <chapter id="api-ac97"> |
| <title>API for AC97 Codec</title> |
| |
| <section> |
| <title>General</title> |
| <para> |
| The ALSA AC97 codec layer is a well-defined one, and you don't |
| have to write many codes to control it. Only low-level control |
| routines are necessary. The AC97 codec API is defined in |
| <filename><sound/ac97_codec.h></filename>. |
| </para> |
| </section> |
| |
| <section id="api-ac97-example"> |
| <title>Full Code Example</title> |
| <para> |
| <example> |
| <title>Example of AC97 Interface</title> |
| <programlisting> |
| <![CDATA[ |
| struct mychip { |
| .... |
| struct snd_ac97 *ac97; |
| .... |
| }; |
| |
| static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, |
| unsigned short reg) |
| { |
| struct mychip *chip = ac97->private_data; |
| .... |
| // read a register value here from the codec |
| return the_register_value; |
| } |
| |
| static void snd_mychip_ac97_write(struct snd_ac97 *ac97, |
| unsigned short reg, unsigned short val) |
| { |
| struct mychip *chip = ac97->private_data; |
| .... |
| // write the given register value to the codec |
| } |
| |
| static int snd_mychip_ac97(struct mychip *chip) |
| { |
| struct snd_ac97_bus *bus; |
| struct snd_ac97_template ac97; |
| int err; |
| static struct snd_ac97_bus_ops ops = { |
| .write = snd_mychip_ac97_write, |
| .read = snd_mychip_ac97_read, |
| }; |
| |
| if ((err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus)) < 0) |
| return err; |
| memset(&ac97, 0, sizeof(ac97)); |
| ac97.private_data = chip; |
| return snd_ac97_mixer(bus, &ac97, &chip->ac97); |
| } |
| |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </section> |
| |
| <section id="api-ac97-constructor"> |
| <title>Constructor</title> |
| <para> |
| For creating an ac97 instance, first call <function>snd_ac97_bus</function> |
| with an <type>ac97_bus_ops_t</type> record with callback functions. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_ac97_bus *bus; |
| static struct snd_ac97_bus_ops ops = { |
| .write = snd_mychip_ac97_write, |
| .read = snd_mychip_ac97_read, |
| }; |
| |
| snd_ac97_bus(card, 0, &ops, NULL, &pbus); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| The bus record is shared among all belonging ac97 instances. |
| </para> |
| |
| <para> |
| And then call <function>snd_ac97_mixer()</function> with an |
| struct <structname>snd_ac97_template</structname> |
| record together with the bus pointer created above. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_ac97_template ac97; |
| int err; |
| |
| memset(&ac97, 0, sizeof(ac97)); |
| ac97.private_data = chip; |
| snd_ac97_mixer(bus, &ac97, &chip->ac97); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where chip->ac97 is the pointer of a newly created |
| <type>ac97_t</type> instance. |
| In this case, the chip pointer is set as the private data, so that |
| the read/write callback functions can refer to this chip instance. |
| This instance is not necessarily stored in the chip |
| record. When you need to change the register values from the |
| driver, or need the suspend/resume of ac97 codecs, keep this |
| pointer to pass to the corresponding functions. |
| </para> |
| </section> |
| |
| <section id="api-ac97-callbacks"> |
| <title>Callbacks</title> |
| <para> |
| The standard callbacks are <structfield>read</structfield> and |
| <structfield>write</structfield>. Obviously they |
| correspond to the functions for read and write accesses to the |
| hardware low-level codes. |
| </para> |
| |
| <para> |
| The <structfield>read</structfield> callback returns the |
| register value specified in the argument. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, |
| unsigned short reg) |
| { |
| struct mychip *chip = ac97->private_data; |
| .... |
| return the_register_value; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| Here, the chip can be cast from ac97->private_data. |
| </para> |
| |
| <para> |
| Meanwhile, the <structfield>write</structfield> callback is |
| used to set the register value. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void snd_mychip_ac97_write(struct snd_ac97 *ac97, |
| unsigned short reg, unsigned short val) |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| These callbacks are non-atomic like the callbacks of control API. |
| </para> |
| |
| <para> |
| There are also other callbacks: |
| <structfield>reset</structfield>, |
| <structfield>wait</structfield> and |
| <structfield>init</structfield>. |
| </para> |
| |
| <para> |
| The <structfield>reset</structfield> callback is used to reset |
| the codec. If the chip requires a special way of reset, you can |
| define this callback. |
| </para> |
| |
| <para> |
| The <structfield>wait</structfield> callback is used for a |
| certain wait at the standard initialization of the codec. If the |
| chip requires the extra wait-time, define this callback. |
| </para> |
| |
| <para> |
| The <structfield>init</structfield> callback is used for |
| additional initialization of the codec. |
| </para> |
| </section> |
| |
| <section id="api-ac97-updating-registers"> |
| <title>Updating Registers in The Driver</title> |
| <para> |
| If you need to access to the codec from the driver, you can |
| call the following functions: |
| <function>snd_ac97_write()</function>, |
| <function>snd_ac97_read()</function>, |
| <function>snd_ac97_update()</function> and |
| <function>snd_ac97_update_bits()</function>. |
| </para> |
| |
| <para> |
| Both <function>snd_ac97_write()</function> and |
| <function>snd_ac97_update()</function> functions are used to |
| set a value to the given register |
| (<constant>AC97_XXX</constant>). The difference between them is |
| that <function>snd_ac97_update()</function> doesn't write a |
| value if the given value has been already set, while |
| <function>snd_ac97_write()</function> always rewrites the |
| value. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_ac97_write(ac97, AC97_MASTER, 0x8080); |
| snd_ac97_update(ac97, AC97_MASTER, 0x8080); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| <function>snd_ac97_read()</function> is used to read the value |
| of the given register. For example, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| value = snd_ac97_read(ac97, AC97_MASTER); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| <function>snd_ac97_update_bits()</function> is used to update |
| some bits of the given register. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_ac97_update_bits(ac97, reg, mask, value); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Also, there is a function to change the sample rate (of a |
| certain register such as |
| <constant>AC97_PCM_FRONT_DAC_RATE</constant>) when VRA or |
| DRA is supported by the codec: |
| <function>snd_ac97_set_rate()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The following registers are available for setting the rate: |
| <constant>AC97_PCM_MIC_ADC_RATE</constant>, |
| <constant>AC97_PCM_FRONT_DAC_RATE</constant>, |
| <constant>AC97_PCM_LR_ADC_RATE</constant>, |
| <constant>AC97_SPDIF</constant>. When the |
| <constant>AC97_SPDIF</constant> is specified, the register is |
| not really changed but the corresponding IEC958 status bits will |
| be updated. |
| </para> |
| </section> |
| |
| <section id="api-ac97-clock-adjustment"> |
| <title>Clock Adjustment</title> |
| <para> |
| On some chip, the clock of the codec isn't 48000 but using a |
| PCI clock (to save a quartz!). In this case, change the field |
| bus->clock to the corresponding |
| value. For example, intel8x0 |
| and es1968 drivers have the auto-measurement function of the |
| clock. |
| </para> |
| </section> |
| |
| <section id="api-ac97-proc-files"> |
| <title>Proc Files</title> |
| <para> |
| The ALSA AC97 interface will create a proc file such as |
| <filename>/proc/asound/card0/codec97#0/ac97#0-0</filename> and |
| <filename>ac97#0-0+regs</filename>. You can refer to these files to |
| see the current status and registers of the codec. |
| </para> |
| </section> |
| |
| <section id="api-ac97-multiple-codecs"> |
| <title>Multiple Codecs</title> |
| <para> |
| When there are several codecs on the same card, you need to |
| call <function>snd_ac97_mixer()</function> multiple times with |
| ac97.num=1 or greater. The <structfield>num</structfield> field |
| specifies the codec |
| number. |
| </para> |
| |
| <para> |
| If you have set up multiple codecs, you need to either write |
| different callbacks for each codec or check |
| ac97->num in the |
| callback routines. |
| </para> |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- MIDI (MPU401-UART) Interface --> |
| <!-- ****************************************************** --> |
| <chapter id="midi-interface"> |
| <title>MIDI (MPU401-UART) Interface</title> |
| |
| <section id="midi-interface-general"> |
| <title>General</title> |
| <para> |
| Many soundcards have built-in MIDI (MPU401-UART) |
| interfaces. When the soundcard supports the standard MPU401-UART |
| interface, most likely you can use the ALSA MPU401-UART API. The |
| MPU401-UART API is defined in |
| <filename><sound/mpu401.h></filename>. |
| </para> |
| |
| <para> |
| Some soundchips have similar but a little bit different |
| implementation of mpu401 stuff. For example, emu10k1 has its own |
| mpu401 routines. |
| </para> |
| </section> |
| |
| <section id="midi-interface-constructor"> |
| <title>Constructor</title> |
| <para> |
| For creating a rawmidi object, call |
| <function>snd_mpu401_uart_new()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_rawmidi *rmidi; |
| snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, integrated, |
| irq, irq_flags, &rmidi); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The first argument is the card pointer, and the second is the |
| index of this component. You can create up to 8 rawmidi |
| devices. |
| </para> |
| |
| <para> |
| The third argument is the type of the hardware, |
| <constant>MPU401_HW_XXX</constant>. If it's not a special one, |
| you can use <constant>MPU401_HW_MPU401</constant>. |
| </para> |
| |
| <para> |
| The 4th argument is the i/o port address. Many |
| backward-compatible MPU401 has an i/o port such as 0x330. Or, it |
| might be a part of its own PCI i/o region. It depends on the |
| chip design. |
| </para> |
| |
| <para> |
| When the i/o port address above is a part of the PCI i/o |
| region, the MPU401 i/o port might have been already allocated |
| (reserved) by the driver itself. In such a case, pass non-zero |
| to the 5th argument |
| (<parameter>integrated</parameter>). Otherwise, pass 0 to it, |
| and |
| the mpu401-uart layer will allocate the i/o ports by itself. |
| </para> |
| |
| <para> |
| Usually, the port address corresponds to the command port and |
| port + 1 corresponds to the data port. If not, you may change |
| the <structfield>cport</structfield> field of |
| struct <structname>snd_mpu401</structname> manually |
| afterward. However, <structname>snd_mpu401</structname> pointer is not |
| returned explicitly by |
| <function>snd_mpu401_uart_new()</function>. You need to cast |
| rmidi->private_data to |
| <structname>snd_mpu401</structname> explicitly, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_mpu401 *mpu; |
| mpu = rmidi->private_data; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| and reset the cport as you like: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| mpu->cport = my_own_control_port; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The 6th argument specifies the irq number for UART. If the irq |
| is already allocated, pass 0 to the 7th argument |
| (<parameter>irq_flags</parameter>). Otherwise, pass the flags |
| for irq allocation |
| (<constant>SA_XXX</constant> bits) to it, and the irq will be |
| reserved by the mpu401-uart layer. If the card doesn't generates |
| UART interrupts, pass -1 as the irq number. Then a timer |
| interrupt will be invoked for polling. |
| </para> |
| </section> |
| |
| <section id="midi-interface-interrupt-handler"> |
| <title>Interrupt Handler</title> |
| <para> |
| When the interrupt is allocated in |
| <function>snd_mpu401_uart_new()</function>, the private |
| interrupt handler is used, hence you don't have to do nothing |
| else than creating the mpu401 stuff. Otherwise, you have to call |
| <function>snd_mpu401_uart_interrupt()</function> explicitly when |
| a UART interrupt is invoked and checked in your own interrupt |
| handler. |
| </para> |
| |
| <para> |
| In this case, you need to pass the private_data of the |
| returned rawmidi object from |
| <function>snd_mpu401_uart_new()</function> as the second |
| argument of <function>snd_mpu401_uart_interrupt()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- RawMIDI Interface --> |
| <!-- ****************************************************** --> |
| <chapter id="rawmidi-interface"> |
| <title>RawMIDI Interface</title> |
| |
| <section id="rawmidi-interface-overview"> |
| <title>Overview</title> |
| |
| <para> |
| The raw MIDI interface is used for hardware MIDI ports that can |
| be accessed as a byte stream. It is not used for synthesizer |
| chips that do not directly understand MIDI. |
| </para> |
| |
| <para> |
| ALSA handles file and buffer management. All you have to do is |
| to write some code to move data between the buffer and the |
| hardware. |
| </para> |
| |
| <para> |
| The rawmidi API is defined in |
| <filename><sound/rawmidi.h></filename>. |
| </para> |
| </section> |
| |
| <section id="rawmidi-interface-constructor"> |
| <title>Constructor</title> |
| |
| <para> |
| To create a rawmidi device, call the |
| <function>snd_rawmidi_new</function> function: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_rawmidi *rmidi; |
| err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi); |
| if (err < 0) |
| return err; |
| rmidi->private_data = chip; |
| strcpy(rmidi->name, "My MIDI"); |
| rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT | |
| SNDRV_RAWMIDI_INFO_INPUT | |
| SNDRV_RAWMIDI_INFO_DUPLEX; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The first argument is the card pointer, the second argument is |
| the ID string. |
| </para> |
| |
| <para> |
| The third argument is the index of this component. You can |
| create up to 8 rawmidi devices. |
| </para> |
| |
| <para> |
| The fourth and fifth arguments are the number of output and |
| input substreams, respectively, of this device. (A substream is |
| the equivalent of a MIDI port.) |
| </para> |
| |
| <para> |
| Set the <structfield>info_flags</structfield> field to specify |
| the capabilities of the device. |
| Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is |
| at least one output port, |
| <constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at |
| least one input port, |
| and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device |
| can handle output and input at the same time. |
| </para> |
| |
| <para> |
| After the rawmidi device is created, you need to set the |
| operators (callbacks) for each substream. There are helper |
| functions to set the operators for all substream of a device: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops); |
| snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The operators are usually defined like this: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct snd_rawmidi_ops snd_mymidi_output_ops = { |
| .open = snd_mymidi_output_open, |
| .close = snd_mymidi_output_close, |
| .trigger = snd_mymidi_output_trigger, |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| These callbacks are explained in the <link |
| linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link> |
| section. |
| </para> |
| |
| <para> |
| If there is more than one substream, you should give each one a |
| unique name: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct list_head *list; |
| struct snd_rawmidi_substream *substream; |
| list_for_each(list, &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams) { |
| substream = list_entry(list, struct snd_rawmidi_substream, list); |
| sprintf(substream->name, "My MIDI Port %d", substream->number + 1); |
| } |
| /* same for SNDRV_RAWMIDI_STREAM_INPUT */ |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| <section id="rawmidi-interface-callbacks"> |
| <title>Callbacks</title> |
| |
| <para> |
| In all callbacks, the private data that you've set for the |
| rawmidi device can be accessed as |
| substream->rmidi->private_data. |
| <!-- <code> isn't available before DocBook 4.3 --> |
| </para> |
| |
| <para> |
| If there is more than one port, your callbacks can determine the |
| port index from the struct snd_rawmidi_substream data passed to each |
| callback: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_rawmidi_substream *substream; |
| int index = substream->number; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <section id="rawmidi-interface-op-open"> |
| <title><function>open</function> callback</title> |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_open(struct snd_rawmidi_substream *substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| <para> |
| This is called when a substream is opened. |
| You can initialize the hardware here, but you should not yet |
| start transmitting/receiving data. |
| </para> |
| </section> |
| |
| <section id="rawmidi-interface-op-close"> |
| <title><function>close</function> callback</title> |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int snd_xxx_close(struct snd_rawmidi_substream *substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| <para> |
| Guess what. |
| </para> |
| |
| <para> |
| The <function>open</function> and <function>close</function> |
| callbacks of a rawmidi device are serialized with a mutex, |
| and can sleep. |
| </para> |
| </section> |
| |
| <section id="rawmidi-interface-op-trigger-out"> |
| <title><function>trigger</function> callback for output |
| substreams</title> |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| <para> |
| This is called with a nonzero <parameter>up</parameter> |
| parameter when there is some data in the substream buffer that |
| must be transmitted. |
| </para> |
| |
| <para> |
| To read data from the buffer, call |
| <function>snd_rawmidi_transmit_peek</function>. It will |
| return the number of bytes that have been read; this will be |
| less than the number of bytes requested when there is no more |
| data in the buffer. |
| After the data has been transmitted successfully, call |
| <function>snd_rawmidi_transmit_ack</function> to remove the |
| data from the substream buffer: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| unsigned char data; |
| while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) { |
| if (snd_mychip_try_to_transmit(data)) |
| snd_rawmidi_transmit_ack(substream, 1); |
| else |
| break; /* hardware FIFO full */ |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| If you know beforehand that the hardware will accept data, you |
| can use the <function>snd_rawmidi_transmit</function> function |
| which reads some data and removes it from the buffer at once: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| while (snd_mychip_transmit_possible()) { |
| unsigned char data; |
| if (snd_rawmidi_transmit(substream, &data, 1) != 1) |
| break; /* no more data */ |
| snd_mychip_transmit(data); |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| If you know beforehand how many bytes you can accept, you can |
| use a buffer size greater than one with the |
| <function>snd_rawmidi_transmit*</function> functions. |
| </para> |
| |
| <para> |
| The <function>trigger</function> callback must not sleep. If |
| the hardware FIFO is full before the substream buffer has been |
| emptied, you have to continue transmitting data later, either |
| in an interrupt handler, or with a timer if the hardware |
| doesn't have a MIDI transmit interrupt. |
| </para> |
| |
| <para> |
| The <function>trigger</function> callback is called with a |
| zero <parameter>up</parameter> parameter when the transmission |
| of data should be aborted. |
| </para> |
| </section> |
| |
| <section id="rawmidi-interface-op-trigger-in"> |
| <title><function>trigger</function> callback for input |
| substreams</title> |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| <para> |
| This is called with a nonzero <parameter>up</parameter> |
| parameter to enable receiving data, or with a zero |
| <parameter>up</parameter> parameter do disable receiving data. |
| </para> |
| |
| <para> |
| The <function>trigger</function> callback must not sleep; the |
| actual reading of data from the device is usually done in an |
| interrupt handler. |
| </para> |
| |
| <para> |
| When data reception is enabled, your interrupt handler should |
| call <function>snd_rawmidi_receive</function> for all received |
| data: |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| void snd_mychip_midi_interrupt(...) |
| { |
| while (mychip_midi_available()) { |
| unsigned char data; |
| data = mychip_midi_read(); |
| snd_rawmidi_receive(substream, &data, 1); |
| } |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| <section id="rawmidi-interface-op-drain"> |
| <title><function>drain</function> callback</title> |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void snd_xxx_drain(struct snd_rawmidi_substream *substream); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| <para> |
| This is only used with output substreams. This function should wait |
| until all data read from the substream buffer has been transmitted. |
| This ensures that the device can be closed and the driver unloaded |
| without losing data. |
| </para> |
| |
| <para> |
| This callback is optional. If you do not set |
| <structfield>drain</structfield> in the struct snd_rawmidi_ops |
| structure, ALSA will simply wait for 50 milliseconds |
| instead. |
| </para> |
| </section> |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Miscellaneous Devices --> |
| <!-- ****************************************************** --> |
| <chapter id="misc-devices"> |
| <title>Miscellaneous Devices</title> |
| |
| <section id="misc-devices-opl3"> |
| <title>FM OPL3</title> |
| <para> |
| The FM OPL3 is still used on many chips (mainly for backward |
| compatibility). ALSA has a nice OPL3 FM control layer, too. The |
| OPL3 API is defined in |
| <filename><sound/opl3.h></filename>. |
| </para> |
| |
| <para> |
| FM registers can be directly accessed through direct-FM API, |
| defined in <filename><sound/asound_fm.h></filename>. In |
| ALSA native mode, FM registers are accessed through |
| Hardware-Dependant Device direct-FM extension API, whereas in |
| OSS compatible mode, FM registers can be accessed with OSS |
| direct-FM compatible API on <filename>/dev/dmfmX</filename> device. |
| </para> |
| |
| <para> |
| For creating the OPL3 component, you have two functions to |
| call. The first one is a constructor for <type>opl3_t</type> |
| instance. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_opl3 *opl3; |
| snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX, |
| integrated, &opl3); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The first argument is the card pointer, the second one is the |
| left port address, and the third is the right port address. In |
| most cases, the right port is placed at the left port + 2. |
| </para> |
| |
| <para> |
| The fourth argument is the hardware type. |
| </para> |
| |
| <para> |
| When the left and right ports have been already allocated by |
| the card driver, pass non-zero to the fifth argument |
| (<parameter>integrated</parameter>). Otherwise, opl3 module will |
| allocate the specified ports by itself. |
| </para> |
| |
| <para> |
| When the accessing to the hardware requires special method |
| instead of the standard I/O access, you can create opl3 instance |
| separately with <function>snd_opl3_new()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_opl3 *opl3; |
| snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Then set <structfield>command</structfield>, |
| <structfield>private_data</structfield> and |
| <structfield>private_free</structfield> for the private |
| access function, the private data and the destructor. |
| The l_port and r_port are not necessarily set. Only the |
| command must be set properly. You can retrieve the data |
| from opl3->private_data field. |
| </para> |
| |
| <para> |
| After creating the opl3 instance via <function>snd_opl3_new()</function>, |
| call <function>snd_opl3_init()</function> to initialize the chip to the |
| proper state. Note that <function>snd_opl3_create()</function> always |
| calls it internally. |
| </para> |
| |
| <para> |
| If the opl3 instance is created successfully, then create a |
| hwdep device for this opl3. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_hwdep *opl3hwdep; |
| snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The first argument is the <type>opl3_t</type> instance you |
| created, and the second is the index number, usually 0. |
| </para> |
| |
| <para> |
| The third argument is the index-offset for the sequencer |
| client assigned to the OPL3 port. When there is an MPU401-UART, |
| give 1 for here (UART always takes 0). |
| </para> |
| </section> |
| |
| <section id="misc-devices-hardware-dependent"> |
| <title>Hardware-Dependent Devices</title> |
| <para> |
| Some chips need the access from the user-space for special |
| controls or for loading the micro code. In such a case, you can |
| create a hwdep (hardware-dependent) device. The hwdep API is |
| defined in <filename><sound/hwdep.h></filename>. You can |
| find examples in opl3 driver or |
| <filename>isa/sb/sb16_csp.c</filename>. |
| </para> |
| |
| <para> |
| Creation of the <type>hwdep</type> instance is done via |
| <function>snd_hwdep_new()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_hwdep *hw; |
| snd_hwdep_new(card, "My HWDEP", 0, &hw); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where the third argument is the index number. |
| </para> |
| |
| <para> |
| You can then pass any pointer value to the |
| <parameter>private_data</parameter>. |
| If you assign a private data, you should define the |
| destructor, too. The destructor function is set to |
| <structfield>private_free</structfield> field. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL); |
| hw->private_data = p; |
| hw->private_free = mydata_free; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| and the implementation of destructor would be: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void mydata_free(struct snd_hwdep *hw) |
| { |
| struct mydata *p = hw->private_data; |
| kfree(p); |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The arbitrary file operations can be defined for this |
| instance. The file operators are defined in |
| <parameter>ops</parameter> table. For example, assume that |
| this chip needs an ioctl. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| hw->ops.open = mydata_open; |
| hw->ops.ioctl = mydata_ioctl; |
| hw->ops.release = mydata_release; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| And implement the callback functions as you like. |
| </para> |
| </section> |
| |
| <section id="misc-devices-IEC958"> |
| <title>IEC958 (S/PDIF)</title> |
| <para> |
| Usually the controls for IEC958 devices are implemented via |
| control interface. There is a macro to compose a name string for |
| IEC958 controls, <function>SNDRV_CTL_NAME_IEC958()</function> |
| defined in <filename><include/asound.h></filename>. |
| </para> |
| |
| <para> |
| There are some standard controls for IEC958 status bits. These |
| controls use the type <type>SNDRV_CTL_ELEM_TYPE_IEC958</type>, |
| and the size of element is fixed as 4 bytes array |
| (value.iec958.status[x]). For <structfield>info</structfield> |
| callback, you don't specify |
| the value field for this type (the count field must be set, |
| though). |
| </para> |
| |
| <para> |
| <quote>IEC958 Playback Con Mask</quote> is used to return the |
| bit-mask for the IEC958 status bits of consumer mode. Similarly, |
| <quote>IEC958 Playback Pro Mask</quote> returns the bitmask for |
| professional mode. They are read-only controls, and are defined |
| as MIXER controls (iface = |
| <constant>SNDRV_CTL_ELEM_IFACE_MIXER</constant>). |
| </para> |
| |
| <para> |
| Meanwhile, <quote>IEC958 Playback Default</quote> control is |
| defined for getting and setting the current default IEC958 |
| bits. Note that this one is usually defined as a PCM control |
| (iface = <constant>SNDRV_CTL_ELEM_IFACE_PCM</constant>), |
| although in some places it's defined as a MIXER control. |
| </para> |
| |
| <para> |
| In addition, you can define the control switches to |
| enable/disable or to set the raw bit mode. The implementation |
| will depend on the chip, but the control should be named as |
| <quote>IEC958 xxx</quote>, preferably using |
| <function>SNDRV_CTL_NAME_IEC958()</function> macro. |
| </para> |
| |
| <para> |
| You can find several cases, for example, |
| <filename>pci/emu10k1</filename>, |
| <filename>pci/ice1712</filename>, or |
| <filename>pci/cmipci.c</filename>. |
| </para> |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Buffer and Memory Management --> |
| <!-- ****************************************************** --> |
| <chapter id="buffer-and-memory"> |
| <title>Buffer and Memory Management</title> |
| |
| <section id="buffer-and-memory-buffer-types"> |
| <title>Buffer Types</title> |
| <para> |
| ALSA provides several different buffer allocation functions |
| depending on the bus and the architecture. All these have a |
| consistent API. The allocation of physically-contiguous pages is |
| done via |
| <function>snd_malloc_xxx_pages()</function> function, where xxx |
| is the bus type. |
| </para> |
| |
| <para> |
| The allocation of pages with fallback is |
| <function>snd_malloc_xxx_pages_fallback()</function>. This |
| function tries to allocate the specified pages but if the pages |
| are not available, it tries to reduce the page sizes until the |
| enough space is found. |
| </para> |
| |
| <para> |
| For releasing the space, call |
| <function>snd_free_xxx_pages()</function> function. |
| </para> |
| |
| <para> |
| Usually, ALSA drivers try to allocate and reserve |
| a large contiguous physical space |
| at the time the module is loaded for the later use. |
| This is called <quote>pre-allocation</quote>. |
| As already written, you can call the following function at the |
| construction of pcm instance (in the case of PCI bus). |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, |
| snd_dma_pci_data(pci), size, max); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where <parameter>size</parameter> is the byte size to be |
| pre-allocated and the <parameter>max</parameter> is the maximal |
| size to be changed via <filename>prealloc</filename> proc file. |
| The allocator will try to get as large area as possible |
| within the given size. |
| </para> |
| |
| <para> |
| The second argument (type) and the third argument (device pointer) |
| are dependent on the bus. |
| In the case of ISA bus, pass <function>snd_dma_isa_data()</function> |
| as the third argument with <constant>SNDRV_DMA_TYPE_DEV</constant> type. |
| For the continuous buffer unrelated to the bus can be pre-allocated |
| with <constant>SNDRV_DMA_TYPE_CONTINUOUS</constant> type and the |
| <function>snd_dma_continuous_data(GFP_KERNEL)</function> device pointer, |
| whereh <constant>GFP_KERNEL</constant> is the kernel allocation flag to |
| use. For the SBUS, <constant>SNDRV_DMA_TYPE_SBUS</constant> and |
| <function>snd_dma_sbus_data(sbus_dev)</function> are used instead. |
| For the PCI scatter-gather buffers, use |
| <constant>SNDRV_DMA_TYPE_DEV_SG</constant> with |
| <function>snd_dma_pci_data(pci)</function> |
| (see the section |
| <link linkend="buffer-and-memory-non-contiguous"><citetitle>Non-Contiguous Buffers |
| </citetitle></link>). |
| </para> |
| |
| <para> |
| Once when the buffer is pre-allocated, you can use the |
| allocator in the <structfield>hw_params</structfield> callback |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_pcm_lib_malloc_pages(substream, size); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| Note that you have to pre-allocate to use this function. |
| </para> |
| </section> |
| |
| <section id="buffer-and-memory-external-hardware"> |
| <title>External Hardware Buffers</title> |
| <para> |
| Some chips have their own hardware buffers and the DMA |
| transfer from the host memory is not available. In such a case, |
| you need to either 1) copy/set the audio data directly to the |
| external hardware buffer, or 2) make an intermediate buffer and |
| copy/set the data from it to the external hardware buffer in |
| interrupts (or in tasklets, preferably). |
| </para> |
| |
| <para> |
| The first case works fine if the external hardware buffer is enough |
| large. This method doesn't need any extra buffers and thus is |
| more effective. You need to define the |
| <structfield>copy</structfield> and |
| <structfield>silence</structfield> callbacks for |
| the data transfer. However, there is a drawback: it cannot |
| be mmapped. The examples are GUS's GF1 PCM or emu8000's |
| wavetable PCM. |
| </para> |
| |
| <para> |
| The second case allows the mmap of the buffer, although you have |
| to handle an interrupt or a tasklet for transferring the data |
| from the intermediate buffer to the hardware buffer. You can find an |
| example in vxpocket driver. |
| </para> |
| |
| <para> |
| Another case is that the chip uses a PCI memory-map |
| region for the buffer instead of the host memory. In this case, |
| mmap is available only on certain architectures like intel. In |
| non-mmap mode, the data cannot be transferred as the normal |
| way. Thus you need to define <structfield>copy</structfield> and |
| <structfield>silence</structfield> callbacks as well |
| as in the cases above. The examples are found in |
| <filename>rme32.c</filename> and <filename>rme96.c</filename>. |
| </para> |
| |
| <para> |
| The implementation of <structfield>copy</structfield> and |
| <structfield>silence</structfield> callbacks depends upon |
| whether the hardware supports interleaved or non-interleaved |
| samples. The <structfield>copy</structfield> callback is |
| defined like below, a bit |
| differently depending whether the direction is playback or |
| capture: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int playback_copy(struct snd_pcm_substream *substream, int channel, |
| snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count); |
| static int capture_copy(struct snd_pcm_substream *substream, int channel, |
| snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| In the case of interleaved samples, the second argument |
| (<parameter>channel</parameter>) is not used. The third argument |
| (<parameter>pos</parameter>) points the |
| current position offset in frames. |
| </para> |
| |
| <para> |
| The meaning of the fourth argument is different between |
| playback and capture. For playback, it holds the source data |
| pointer, and for capture, it's the destination data pointer. |
| </para> |
| |
| <para> |
| The last argument is the number of frames to be copied. |
| </para> |
| |
| <para> |
| What you have to do in this callback is again different |
| between playback and capture directions. In the case of |
| playback, you do: copy the given amount of data |
| (<parameter>count</parameter>) at the specified pointer |
| (<parameter>src</parameter>) to the specified offset |
| (<parameter>pos</parameter>) on the hardware buffer. When |
| coded like memcpy-like way, the copy would be like: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src, |
| frames_to_bytes(runtime, count)); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| For the capture direction, you do: copy the given amount of |
| data (<parameter>count</parameter>) at the specified offset |
| (<parameter>pos</parameter>) on the hardware buffer to the |
| specified pointer (<parameter>dst</parameter>). |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos), |
| frames_to_bytes(runtime, count)); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| Note that both of the position and the data amount are given |
| in frames. |
| </para> |
| |
| <para> |
| In the case of non-interleaved samples, the implementation |
| will be a bit more complicated. |
| </para> |
| |
| <para> |
| You need to check the channel argument, and if it's -1, copy |
| the whole channels. Otherwise, you have to copy only the |
| specified channel. Please check |
| <filename>isa/gus/gus_pcm.c</filename> as an example. |
| </para> |
| |
| <para> |
| The <structfield>silence</structfield> callback is also |
| implemented in a similar way. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int silence(struct snd_pcm_substream *substream, int channel, |
| snd_pcm_uframes_t pos, snd_pcm_uframes_t count); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The meanings of arguments are identical with the |
| <structfield>copy</structfield> |
| callback, although there is no <parameter>src/dst</parameter> |
| argument. In the case of interleaved samples, the channel |
| argument has no meaning, as well as on |
| <structfield>copy</structfield> callback. |
| </para> |
| |
| <para> |
| The role of <structfield>silence</structfield> callback is to |
| set the given amount |
| (<parameter>count</parameter>) of silence data at the |
| specified offset (<parameter>pos</parameter>) on the hardware |
| buffer. Suppose that the data format is signed (that is, the |
| silent-data is 0), and the implementation using a memset-like |
| function would be like: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0, |
| frames_to_bytes(runtime, count)); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| In the case of non-interleaved samples, again, the |
| implementation becomes a bit more complicated. See, for example, |
| <filename>isa/gus/gus_pcm.c</filename>. |
| </para> |
| </section> |
| |
| <section id="buffer-and-memory-non-contiguous"> |
| <title>Non-Contiguous Buffers</title> |
| <para> |
| If your hardware supports the page table like emu10k1 or the |
| buffer descriptors like via82xx, you can use the scatter-gather |
| (SG) DMA. ALSA provides an interface for handling SG-buffers. |
| The API is provided in <filename><sound/pcm.h></filename>. |
| </para> |
| |
| <para> |
| For creating the SG-buffer handler, call |
| <function>snd_pcm_lib_preallocate_pages()</function> or |
| <function>snd_pcm_lib_preallocate_pages_for_all()</function> |
| with <constant>SNDRV_DMA_TYPE_DEV_SG</constant> |
| in the PCM constructor like other PCI pre-allocator. |
| You need to pass the <function>snd_dma_pci_data(pci)</function>, |
| where pci is the struct <structname>pci_dev</structname> pointer |
| of the chip as well. |
| The <type>snd_sg_buf_t</type> instance is created as |
| substream->dma_private. You can cast |
| the pointer like: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_sg_buf *sgbuf = (struct snd_sg_buf_t*)substream->dma_private; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Then call <function>snd_pcm_lib_malloc_pages()</function> |
| in <structfield>hw_params</structfield> callback |
| as well as in the case of normal PCI buffer. |
| The SG-buffer handler will allocate the non-contiguous kernel |
| pages of the given size and map them onto the virtually contiguous |
| memory. The virtual pointer is addressed in runtime->dma_area. |
| The physical address (runtime->dma_addr) is set to zero, |
| because the buffer is physically non-contigous. |
| The physical address table is set up in sgbuf->table. |
| You can get the physical address at a certain offset via |
| <function>snd_pcm_sgbuf_get_addr()</function>. |
| </para> |
| |
| <para> |
| When a SG-handler is used, you need to set |
| <function>snd_pcm_sgbuf_ops_page</function> as |
| the <structfield>page</structfield> callback. |
| (See <link linkend="pcm-interface-operators-page-callback"> |
| <citetitle>page callback section</citetitle></link>.) |
| </para> |
| |
| <para> |
| For releasing the data, call |
| <function>snd_pcm_lib_free_pages()</function> in the |
| <structfield>hw_free</structfield> callback as usual. |
| </para> |
| </section> |
| |
| <section id="buffer-and-memory-vmalloced"> |
| <title>Vmalloc'ed Buffers</title> |
| <para> |
| It's possible to use a buffer allocated via |
| <function>vmalloc</function>, for example, for an intermediate |
| buffer. Since the allocated pages are not contiguous, you need |
| to set the <structfield>page</structfield> callback to obtain |
| the physical address at every offset. |
| </para> |
| |
| <para> |
| The implementation of <structfield>page</structfield> callback |
| would be like this: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| #include <linux/vmalloc.h> |
| |
| /* get the physical page pointer on the given offset */ |
| static struct page *mychip_page(struct snd_pcm_substream *substream, |
| unsigned long offset) |
| { |
| void *pageptr = substream->runtime->dma_area + offset; |
| return vmalloc_to_page(pageptr); |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </section> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Proc Interface --> |
| <!-- ****************************************************** --> |
| <chapter id="proc-interface"> |
| <title>Proc Interface</title> |
| <para> |
| ALSA provides an easy interface for procfs. The proc files are |
| very useful for debugging. I recommend you set up proc files if |
| you write a driver and want to get a running status or register |
| dumps. The API is found in |
| <filename><sound/info.h></filename>. |
| </para> |
| |
| <para> |
| For creating a proc file, call |
| <function>snd_card_proc_new()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| struct snd_info_entry *entry; |
| int err = snd_card_proc_new(card, "my-file", &entry); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where the second argument specifies the proc-file name to be |
| created. The above example will create a file |
| <filename>my-file</filename> under the card directory, |
| e.g. <filename>/proc/asound/card0/my-file</filename>. |
| </para> |
| |
| <para> |
| Like other components, the proc entry created via |
| <function>snd_card_proc_new()</function> will be registered and |
| released automatically in the card registration and release |
| functions. |
| </para> |
| |
| <para> |
| When the creation is successful, the function stores a new |
| instance at the pointer given in the third argument. |
| It is initialized as a text proc file for read only. For using |
| this proc file as a read-only text file as it is, set the read |
| callback with a private data via |
| <function>snd_info_set_text_ops()</function>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_info_set_text_ops(entry, chip, read_size, my_proc_read); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| where the second argument (<parameter>chip</parameter>) is the |
| private data to be used in the callbacks. The third parameter |
| specifies the read buffer size and the fourth |
| (<parameter>my_proc_read</parameter>) is the callback function, which |
| is defined like |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void my_proc_read(struct snd_info_entry *entry, |
| struct snd_info_buffer *buffer); |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| </para> |
| |
| <para> |
| In the read callback, use <function>snd_iprintf()</function> for |
| output strings, which works just like normal |
| <function>printf()</function>. For example, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void my_proc_read(struct snd_info_entry *entry, |
| struct snd_info_buffer *buffer) |
| { |
| struct my_chip *chip = entry->private_data; |
| |
| snd_iprintf(buffer, "This is my chip!\n"); |
| snd_iprintf(buffer, "Port = %ld\n", chip->port); |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The file permission can be changed afterwards. As default, it's |
| set as read only for all users. If you want to add the write |
| permission to the user (root as default), set like below: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| entry->mode = S_IFREG | S_IRUGO | S_IWUSR; |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| and set the write buffer size and the callback |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| entry->c.text.write_size = 256; |
| entry->c.text.write = my_proc_write; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The buffer size for read is set to 1024 implicitly by |
| <function>snd_info_set_text_ops()</function>. It should suffice |
| in most cases (the size will be aligned to |
| <constant>PAGE_SIZE</constant> anyway), but if you need to handle |
| very large text files, you can set it explicitly, too. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| entry->c.text.read_size = 65536; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| For the write callback, you can use |
| <function>snd_info_get_line()</function> to get a text line, and |
| <function>snd_info_get_str()</function> to retrieve a string from |
| the line. Some examples are found in |
| <filename>core/oss/mixer_oss.c</filename>, core/oss/and |
| <filename>pcm_oss.c</filename>. |
| </para> |
| |
| <para> |
| For a raw-data proc-file, set the attributes like the following: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct snd_info_entry_ops my_file_io_ops = { |
| .read = my_file_io_read, |
| }; |
| |
| entry->content = SNDRV_INFO_CONTENT_DATA; |
| entry->private_data = chip; |
| entry->c.ops = &my_file_io_ops; |
| entry->size = 4096; |
| entry->mode = S_IFREG | S_IRUGO; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The callback is much more complicated than the text-file |
| version. You need to use a low-level i/o functions such as |
| <function>copy_from/to_user()</function> to transfer the |
| data. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static long my_file_io_read(struct snd_info_entry *entry, |
| void *file_private_data, |
| struct file *file, |
| char *buf, |
| unsigned long count, |
| unsigned long pos) |
| { |
| long size = count; |
| if (pos + size > local_max_size) |
| size = local_max_size - pos; |
| if (copy_to_user(buf, local_data + pos, size)) |
| return -EFAULT; |
| return size; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Power Management --> |
| <!-- ****************************************************** --> |
| <chapter id="power-management"> |
| <title>Power Management</title> |
| <para> |
| If the chip is supposed to work with with suspend/resume |
| functions, you need to add the power-management codes to the |
| driver. The additional codes for the power-management should be |
| <function>ifdef</function>'ed with |
| <constant>CONFIG_PM</constant>. |
| </para> |
| |
| <para> |
| ALSA provides the common power-management layer. Each card driver |
| needs to have only low-level suspend and resume callbacks. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| #ifdef CONFIG_PM |
| static int snd_my_suspend(struct snd_card *card, pm_message_t state) |
| { |
| .... // do things for suspsend |
| return 0; |
| } |
| static int snd_my_resume(struct snd_card *card) |
| { |
| .... // do things for suspsend |
| return 0; |
| } |
| #endif |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The scheme of the real suspend job is as following. |
| |
| <orderedlist> |
| <listitem><para>Retrieve the chip data from pm_private_data field.</para></listitem> |
| <listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem> |
| <listitem><para>Save the register values if necessary.</para></listitem> |
| <listitem><para>Stop the hardware if necessary.</para></listitem> |
| <listitem><para>Disable the PCI device by calling <function>pci_disable_device()</function>.</para></listitem> |
| </orderedlist> |
| </para> |
| |
| <para> |
| A typical code would be like: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int mychip_suspend(struct snd_card *card, pm_message_t state) |
| { |
| /* (1) */ |
| struct mychip *chip = card->pm_private_data; |
| /* (2) */ |
| snd_pcm_suspend_all(chip->pcm); |
| /* (3) */ |
| snd_mychip_save_registers(chip); |
| /* (4) */ |
| snd_mychip_stop_hardware(chip); |
| /* (5) */ |
| pci_disable_device(chip->pci); |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The scheme of the real resume job is as following. |
| |
| <orderedlist> |
| <listitem><para>Retrieve the chip data from pm_private_data field.</para></listitem> |
| <listitem><para>Enable the pci device again by calling |
| <function>pci_enable_device()</function>.</para></listitem> |
| <listitem><para>Re-initialize the chip.</para></listitem> |
| <listitem><para>Restore the saved registers if necessary.</para></listitem> |
| <listitem><para>Resume the mixer, e.g. calling |
| <function>snd_ac97_resume()</function>.</para></listitem> |
| <listitem><para>Restart the hardware (if any).</para></listitem> |
| </orderedlist> |
| </para> |
| |
| <para> |
| A typical code would be like: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static void mychip_resume(struct mychip *chip) |
| { |
| /* (1) */ |
| struct mychip *chip = card->pm_private_data; |
| /* (2) */ |
| pci_enable_device(chip->pci); |
| /* (3) */ |
| snd_mychip_reinit_chip(chip); |
| /* (4) */ |
| snd_mychip_restore_registers(chip); |
| /* (5) */ |
| snd_ac97_resume(chip->ac97); |
| /* (6) */ |
| snd_mychip_restart_chip(chip); |
| return 0; |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| OK, we have all callbacks now. Let's set up them now. In the |
| initialization of the card, add the following: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int __devinit snd_mychip_probe(struct pci_dev *pci, |
| const struct pci_device_id *pci_id) |
| { |
| .... |
| struct snd_card *card; |
| struct mychip *chip; |
| .... |
| snd_card_set_pm_callback(card, snd_my_suspend, snd_my_resume, chip); |
| .... |
| } |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| Here you don't have to put ifdef CONFIG_PM around, since it's already |
| checked in the header and expanded to empty if not needed. |
| </para> |
| |
| <para> |
| If you need a space for saving the registers, you'll need to |
| allocate the buffer for it here, too, since it would be fatal |
| if you cannot allocate a memory in the suspend phase. |
| The allocated buffer should be released in the corresponding |
| destructor. |
| </para> |
| |
| <para> |
| And next, set suspend/resume callbacks to the pci_driver, |
| This can be done by passing a macro SND_PCI_PM_CALLBACKS |
| in the pci_driver struct. This macro is expanded to the correct |
| (global) callbacks if CONFIG_PM is set. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static struct pci_driver driver = { |
| .name = "My Chip", |
| .id_table = snd_my_ids, |
| .probe = snd_my_probe, |
| .remove = __devexit_p(snd_my_remove), |
| SND_PCI_PM_CALLBACKS |
| }; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Module Parameters --> |
| <!-- ****************************************************** --> |
| <chapter id="module-parameters"> |
| <title>Module Parameters</title> |
| <para> |
| There are standard module options for ALSA. At least, each |
| module should have <parameter>index</parameter>, |
| <parameter>id</parameter> and <parameter>enable</parameter> |
| options. |
| </para> |
| |
| <para> |
| If the module supports multiple cards (usually up to |
| 8 = <constant>SNDRV_CARDS</constant> cards), they should be |
| arrays. The default initial values are defined already as |
| constants for ease of programming: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; |
| static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; |
| static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| If the module supports only a single card, they could be single |
| variables, instead. <parameter>enable</parameter> option is not |
| always necessary in this case, but it wouldn't be so bad to have a |
| dummy option for compatibility. |
| </para> |
| |
| <para> |
| The module parameters must be declared with the standard |
| <function>module_param()()</function>, |
| <function>module_param_array()()</function> and |
| <function>MODULE_PARM_DESC()</function> macros. |
| </para> |
| |
| <para> |
| The typical coding would be like below: |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| #define CARD_NAME "My Chip" |
| |
| module_param_array(index, int, NULL, 0444); |
| MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard."); |
| module_param_array(id, charp, NULL, 0444); |
| MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard."); |
| module_param_array(enable, bool, NULL, 0444); |
| MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard."); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| Also, don't forget to define the module description, classes, |
| license and devices. Especially, the recent modprobe requires to |
| define the module license as GPL, etc., otherwise the system is |
| shown as <quote>tainted</quote>. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| MODULE_DESCRIPTION("My Chip"); |
| MODULE_LICENSE("GPL"); |
| MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}"); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- How To Put Your Driver --> |
| <!-- ****************************************************** --> |
| <chapter id="how-to-put-your-driver"> |
| <title>How To Put Your Driver Into ALSA Tree</title> |
| <section> |
| <title>General</title> |
| <para> |
| So far, you've learned how to write the driver codes. |
| And you might have a question now: how to put my own |
| driver into the ALSA driver tree? |
| Here (finally :) the standard procedure is described briefly. |
| </para> |
| |
| <para> |
| Suppose that you'll create a new PCI driver for the card |
| <quote>xyz</quote>. The card module name would be |
| snd-xyz. The new driver is usually put into alsa-driver |
| tree, <filename>alsa-driver/pci</filename> directory in |
| the case of PCI cards. |
| Then the driver is evaluated, audited and tested |
| by developers and users. After a certain time, the driver |
| will go to alsa-kernel tree (to the corresponding directory, |
| such as <filename>alsa-kernel/pci</filename>) and eventually |
| integrated into Linux 2.6 tree (the directory would be |
| <filename>linux/sound/pci</filename>). |
| </para> |
| |
| <para> |
| In the following sections, the driver code is supposed |
| to be put into alsa-driver tree. The two cases are assumed: |
| a driver consisting of a single source file and one consisting |
| of several source files. |
| </para> |
| </section> |
| |
| <section> |
| <title>Driver with A Single Source File</title> |
| <para> |
| <orderedlist> |
| <listitem> |
| <para> |
| Modify alsa-driver/pci/Makefile |
| </para> |
| |
| <para> |
| Suppose you have a file xyz.c. Add the following |
| two lines |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd-xyz-objs := xyz.o |
| obj-$(CONFIG_SND_XYZ) += snd-xyz.o |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| Create the Kconfig entry |
| </para> |
| |
| <para> |
| Add the new entry of Kconfig for your xyz driver. |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| config SND_XYZ |
| tristate "Foobar XYZ" |
| depends on SND |
| select SND_PCM |
| help |
| Say Y here to include support for Foobar XYZ soundcard. |
| |
| To compile this driver as a module, choose M here: the module |
| will be called snd-xyz. |
| ]]> |
| </programlisting> |
| </informalexample> |
| |
| the line, select SND_PCM, specifies that the driver xyz supports |
| PCM. In addition to SND_PCM, the following components are |
| supported for select command: |
| SND_RAWMIDI, SND_TIMER, SND_HWDEP, SND_MPU401_UART, |
| SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, SND_AC97_CODEC. |
| Add the select command for each supported component. |
| </para> |
| |
| <para> |
| Note that some selections imply the lowlevel selections. |
| For example, PCM includes TIMER, MPU401_UART includes RAWMIDI, |
| AC97_CODEC includes PCM, and OPL3_LIB includes HWDEP. |
| You don't need to give the lowlevel selections again. |
| </para> |
| |
| <para> |
| For the details of Kconfig script, refer to the kbuild |
| documentation. |
| </para> |
| |
| </listitem> |
| |
| <listitem> |
| <para> |
| Run cvscompile script to re-generate the configure script and |
| build the whole stuff again. |
| </para> |
| </listitem> |
| </orderedlist> |
| </para> |
| </section> |
| |
| <section> |
| <title>Drivers with Several Source Files</title> |
| <para> |
| Suppose that the driver snd-xyz have several source files. |
| They are located in the new subdirectory, |
| pci/xyz. |
| |
| <orderedlist> |
| <listitem> |
| <para> |
| Add a new directory (<filename>xyz</filename>) in |
| <filename>alsa-driver/pci/Makefile</filename> like below |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| obj-$(CONFIG_SND) += xyz/ |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| Under the directory <filename>xyz</filename>, create a Makefile |
| |
| <example> |
| <title>Sample Makefile for a driver xyz</title> |
| <programlisting> |
| <![CDATA[ |
| ifndef SND_TOPDIR |
| SND_TOPDIR=../.. |
| endif |
| |
| include $(SND_TOPDIR)/toplevel.config |
| include $(SND_TOPDIR)/Makefile.conf |
| |
| snd-xyz-objs := xyz.o abc.o def.o |
| |
| obj-$(CONFIG_SND_XYZ) += snd-xyz.o |
| |
| include $(SND_TOPDIR)/Rules.make |
| ]]> |
| </programlisting> |
| </example> |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| Create the Kconfig entry |
| </para> |
| |
| <para> |
| This procedure is as same as in the last section. |
| </para> |
| </listitem> |
| |
| <listitem> |
| <para> |
| Run cvscompile script to re-generate the configure script and |
| build the whole stuff again. |
| </para> |
| </listitem> |
| </orderedlist> |
| </para> |
| </section> |
| |
| </chapter> |
| |
| <!-- ****************************************************** --> |
| <!-- Useful Functions --> |
| <!-- ****************************************************** --> |
| <chapter id="useful-functions"> |
| <title>Useful Functions</title> |
| |
| <section id="useful-functions-snd-printk"> |
| <title><function>snd_printk()</function> and friends</title> |
| <para> |
| ALSA provides a verbose version of |
| <function>printk()</function> function. If a kernel config |
| <constant>CONFIG_SND_VERBOSE_PRINTK</constant> is set, this |
| function prints the given message together with the file name |
| and the line of the caller. The <constant>KERN_XXX</constant> |
| prefix is processed as |
| well as the original <function>printk()</function> does, so it's |
| recommended to add this prefix, e.g. |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\n"); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| There are also <function>printk()</function>'s for |
| debugging. <function>snd_printd()</function> can be used for |
| general debugging purposes. If |
| <constant>CONFIG_SND_DEBUG</constant> is set, this function is |
| compiled, and works just like |
| <function>snd_printk()</function>. If the ALSA is compiled |
| without the debugging flag, it's ignored. |
| </para> |
| |
| <para> |
| <function>snd_printdd()</function> is compiled in only when |
| <constant>CONFIG_SND_DEBUG_DETECT</constant> is set. Please note |
| that <constant>DEBUG_DETECT</constant> is not set as default |
| even if you configure the alsa-driver with |
| <option>--with-debug=full</option> option. You need to give |
| explicitly <option>--with-debug=detect</option> option instead. |
| </para> |
| </section> |
| |
| <section id="useful-functions-snd-assert"> |
| <title><function>snd_assert()</function></title> |
| <para> |
| <function>snd_assert()</function> macro is similar with the |
| normal <function>assert()</function> macro. For example, |
| |
| <informalexample> |
| <programlisting> |
| <![CDATA[ |
| snd_assert(pointer != NULL, return -EINVAL); |
| ]]> |
| </programlisting> |
| </informalexample> |
| </para> |
| |
| <para> |
| The first argument is the expression to evaluate, and the |
| second argument is the action if it fails. When |
| <constant>CONFIG_SND_DEBUG</constant>, is set, it will show an |
| error message such as <computeroutput>BUG? (xxx)</computeroutput> |
| together with stack trace. |
| </para> |
| <para> |
| When no debug flag is set, this macro is ignored. |
| </para> |
| </section> |
| |
| <section id="useful-functions-snd-bug"> |
| <title><function>snd_BUG()</function></title> |
| <para> |
| It shows <computeroutput>BUG?</computeroutput> message and |
| stack trace as well as <function>snd_assert</function> at the point. |
| It's useful to show that a fatal error happens there. |
| </para> |
| <para> |
| When no debug flag is set, this macro is ignored. |
| </para> |
| </section> |
| </chapter> |
| |
| |
| <!-- ****************************************************** --> |
| <!-- Acknowledgments --> |
| <!-- ****************************************************** --> |
| <chapter id="acknowledments"> |
| <title>Acknowledgments</title> |
| <para> |
| I would like to thank Phil Kerr for his help for improvement and |
| corrections of this document. |
| </para> |
| <para> |
| Kevin Conder reformatted the original plain-text to the |
| DocBook format. |
| </para> |
| <para> |
| Giuliano Pochini corrected typos and contributed the example codes |
| in the hardware constraints section. |
| </para> |
| </chapter> |
| |
| |
| </book> |