dtbhtool/dtbtool.txt

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June 2014, Ketut Putu Kumajaya
Samsung Exynos DTBH device tree documentation.


Android - Table of Device Tree
==============================

0) Document revision
   v1.0 - Initial version (dng)

1) Android boot image:
----------------------
1.1) Header:
   1) Magic (8B)
   2) kernel size (4B)
   3) kernel addr (4B)
   4) ramdisk size (4B)
   5) ramdisk addr (4B)
   6) 2ndary size (4B)
   7) 2ndary addr (4B)
   8) tags addr (4B)
   9) page size (4B)
  10) unused #1 (4B) (zero in standard Android)
  11) unused #2 (4B) (zero in standard Android)
  12) product name (16B)
  13) kernel cmdline (512B)
  14) id (8B)

1.2) Layout:
   A) header (as above - 1 page)
   B) kernel (n pages)
   C) ramdisk (m pages)
   D) second stage (o pages)

2) Exynos DTBH table of device tree
--------------------------
2.1) Changes:
   i) use "unused #1, #2" members in existing boot image
      header to point to new table of device tree
      (#1 - size of Exynos DTBH table of DT)
  ii) append table of device tree (described later)
      after "D) second stage"

2.2) Format:
                                 size
   x      +------------------+
   |      | MAGIC ("DTBH")   |   4B
   |      +------------------+
 header   | VERSION          |   uint32 (version 2, 0x00000002)
   |      +------------------+
   |      | num of DTBs      |   uint32 (number of DTB entries, e.g. 5 entries, 0x00000005)
   x      +------------------+
   |      | chip #1          |   uint32 (e.g. ID for 5422, 0x0000152e)
   |      +------------------+
   |      | platform #1      |   uint32 (e.g. ID for k3g, 0x00001e92)
   |      +------------------+
 device   | subtype #1       |   uint32 (e.g. ID for k3g_eur_open, 0x7d64f612)
  #1      +------------------+
 entry    | hw_rev #1        |   uint32 (e.g. k3g rev 2, 0x00000002)
   |      +------------------+
   |      | hw_rev_end #1    |   uint32 (e.g. k3g rev_end 2, 0x00000002)
   |      +------------------+
   |      | offset #1        |   uint32 (byte offset from start/before MAGIC
   |      +------------------+           to DTB entry, e.g. 0x00000800)
   |      | size #1          |   uint32 (size in bytes of DTB blob
   |      +------------------+           e.g. 110,592 bytes, 0x0001b000)
   |      | space #1         |   uint32 (0x00000020)
   x      +------------------+
   .              .
   .              .  (repeat)
   .              .

   x      +------------------+
   |      | chip #Z          |   uint32 (e.g. ID for 5422, 0x0000152e)
   |      +------------------+
   |      | platform #Z      |   uint32 (e.g. ID for k3g, 0x00001e92)
   |      +------------------+
 device   | subtype #Z       |   uint32 (e.g. ID for k3g_eur_open, 0x7d64f612)
  #1      +------------------+
 entry    | hw_rev #Z        |   uint32 (e.g. k3g rev 10, 0x0000000A)
   |      +------------------+
   |      | hw_rev_end #Z    |   uint32 (e.g. k3g rev_end 255, 0x000000FF)
   |      +------------------+
   |      | offset #Z        |   uint32 (byte offset from start/before MAGIC
   |      +------------------+           to DTB entry, e.g. 0x0006c800)
   |      | size #Z          |   uint32 (size in bytes of DTB blob
   |      +------------------+           e.g. 110,592 bytes, 0x0001b000)
   |      | space #Z         |   uint32 (0x00000020)
   x      +------------------+
          | padding          |   variable length for next DTB to start on
          +------------------+           page boundary
          | DTB #1           |   variable (start is page aligned)
          |                  |
          |                  |
          +------------------+
          | padding          |   variable length for next DTB to start on
          +------------------+           page boundary
                  .
                  .
                  .

          +------------------+
          | DTB #Z (last)    |   variable (start is page aligned)
          |                  |
          |                  |
          +------------------+