| Kernel driver ds1621 |
| ==================== |
| |
| Supported chips: |
| * Dallas Semiconductor / Maxim Integrated DS1621 |
| Prefix: 'ds1621' |
| Addresses scanned: none |
| Datasheet: Publicly available from www.maximintegrated.com |
| |
| * Dallas Semiconductor DS1625 |
| Prefix: 'ds1625' |
| Addresses scanned: none |
| Datasheet: Publicly available from www.datasheetarchive.com |
| |
| * Maxim Integrated DS1631 |
| Prefix: 'ds1631' |
| Addresses scanned: none |
| Datasheet: Publicly available from www.maximintegrated.com |
| |
| * Maxim Integrated DS1721 |
| Prefix: 'ds1721' |
| Addresses scanned: none |
| Datasheet: Publicly available from www.maximintegrated.com |
| |
| * Maxim Integrated DS1731 |
| Prefix: 'ds1731' |
| Addresses scanned: none |
| Datasheet: Publicly available from www.maximintegrated.com |
| |
| Authors: |
| Christian W. Zuckschwerdt <zany@triq.net> |
| valuable contributions by Jan M. Sendler <sendler@sendler.de> |
| ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net> |
| with the help of Jean Delvare <jdelvare@suse.de> |
| |
| Module Parameters |
| ------------------ |
| |
| * polarity int |
| Output's polarity: 0 = active high, 1 = active low |
| |
| Description |
| ----------- |
| |
| The DS1621 is a (one instance) digital thermometer and thermostat. It has |
| both high and low temperature limits which can be user defined (i.e. |
| programmed into non-volatile on-chip registers). Temperature range is -55 |
| degree Celsius to +125 in 0.5 increments. You may convert this into a |
| Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity |
| parameter is not provided, original value is used. |
| |
| As for the thermostat, behavior can also be programmed using the polarity |
| toggle. On the one hand ("heater"), the thermostat output of the chip, |
| Tout, will trigger when the low limit temperature is met or underrun and |
| stays high until the high limit is met or exceeded. On the other hand |
| ("cooler"), vice versa. That way "heater" equals "active low", whereas |
| "conditioner" equals "active high". Please note that the DS1621 data sheet |
| is somewhat misleading in this point since setting the polarity bit does |
| not simply invert Tout. |
| |
| A second thing is that, during extensive testing, Tout showed a tolerance |
| of up to +/- 0.5 degrees even when compared against precise temperature |
| readings. Be sure to have a high vs. low temperature limit gap of al least |
| 1.0 degree Celsius to avoid Tout "bouncing", though! |
| |
| The alarm bits are set when the high or low limits are met or exceeded and |
| are reset by the module as soon as the respective temperature ranges are |
| left. |
| |
| The alarm registers are in no way suitable to find out about the actual |
| status of Tout. They will only tell you about its history, whether or not |
| any of the limits have ever been met or exceeded since last power-up or |
| reset. Be aware: When testing, it showed that the status of Tout can change |
| with neither of the alarms set. |
| |
| Since there is no version or vendor identification register, there is |
| no unique identification for these devices. Therefore, explicit device |
| instantiation is required for correct device identification and functionality |
| (one device per address in this address range: 0x48..0x4f). |
| |
| The DS1625 is pin compatible and functionally equivalent with the DS1621, |
| but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are |
| also pin compatible with the DS1621 and provide multi-resolution support. |
| |
| Additionally, the DS1721 data sheet says the temperature flags (THF and TLF) |
| are used internally, however, these flags do get set and cleared as the actual |
| temperature crosses the min or max settings (which by default are set to 75 |
| and 80 degrees respectively). |
| |
| Temperature Conversion: |
| ----------------------- |
| DS1621 - 750ms (older devices may take up to 1000ms) |
| DS1625 - 500ms |
| DS1631 - 93ms..750ms for 9..12 bits resolution, respectively. |
| DS1721 - 93ms..750ms for 9..12 bits resolution, respectively. |
| DS1731 - 93ms..750ms for 9..12 bits resolution, respectively. |
| |
| Note: |
| On the DS1621, internal access to non-volatile registers may last for 10ms |
| or less (unverified on the other devices). |
| |
| Temperature Accuracy: |
| --------------------- |
| DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees) |
| DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees) |
| DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees) |
| DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees) |
| DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees) |
| |
| Note: |
| Please refer to the device datasheets for accuracy at other temperatures. |
| |
| Temperature Resolution: |
| ----------------------- |
| As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution |
| support, which is achieved via the R0 and R1 config register bits, where: |
| |
| R0..R1 |
| ------ |
| 0 0 => 9 bits, 0.5 degrees Celsius |
| 1 0 => 10 bits, 0.25 degrees Celsius |
| 0 1 => 11 bits, 0.125 degrees Celsius |
| 1 1 => 12 bits, 0.0625 degrees Celsius |
| |
| Note: |
| At initial device power-on, the default resolution is set to 12-bits. |
| |
| The resolution mode for the DS1631, DS1721, or DS1731 can be changed from |
| userspace, via the device 'update_interval' sysfs attribute. This attribute |
| will normalize the range of input values to the device maximum resolution |
| values defined in the datasheet as follows: |
| |
| Resolution Conversion Time Input Range |
| (C/LSB) (msec) (msec) |
| ------------------------------------------------ |
| 0.5 93.75 0....94 |
| 0.25 187.5 95...187 |
| 0.125 375 188..375 |
| 0.0625 750 376..infinity |
| ------------------------------------------------ |
| |
| The following examples show how the 'update_interval' attribute can be |
| used to change the conversion time: |
| |
| $ cat update_interval |
| 750 |
| $ cat temp1_input |
| 22062 |
| $ |
| $ echo 300 > update_interval |
| $ cat update_interval |
| 375 |
| $ cat temp1_input |
| 22125 |
| $ |
| $ echo 150 > update_interval |
| $ cat update_interval |
| 188 |
| $ cat temp1_input |
| 22250 |
| $ |
| $ echo 1 > update_interval |
| $ cat update_interval |
| 94 |
| $ cat temp1_input |
| 22000 |
| $ |
| $ echo 1000 > update_interval |
| $ cat update_interval |
| 750 |
| $ cat temp1_input |
| 22062 |
| $ |
| |
| As shown, the ds1621 driver automatically adjusts the 'update_interval' |
| user input, via a step function. Reading back the 'update_interval' value |
| after a write operation provides the conversion time used by the device. |
| |
| Mathematically, the resolution can be derived from the conversion time |
| via the following function: |
| |
| g(x) = 0.5 * [minimum_conversion_time/x] |
| |
| where: |
| -> 'x' = the output from 'update_interval' |
| -> 'g(x)' = the resolution in degrees C per LSB. |
| -> 93.75ms = minimum conversion time |