psb.rst 6.0 KB

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  1. i.MX7D/i.MX8MM SRC_GPR10 PERSIST_SECONDARY_BOOT for bootloader A/B switching
  2. ============================================================================
  3. Introduction
  4. ------------
  5. Since at least iMX53 until iMX8MM, it is possible to have two copies of
  6. bootloader in SD/eMMC and switch between them. The switch is triggered
  7. either by the BootROM in case the bootloader image is faulty OR can be
  8. enforced by the user.
  9. Operation
  10. ---------
  11. #. Upon Power-On Reset (POR)
  12. - SRC_GPR10 bit PERSIST_SECONDARY_BOOT is set to 0
  13. - BootROM attempts to start bootloader A-copy
  14. - if A-copy valid
  15. - BootROM starts A-copy
  16. - END
  17. - if A-copy NOT valid
  18. - BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1
  19. - BootROM triggers WARM reset, GOTO 1)
  20. - END
  21. #. Upon COLD Reset
  22. - GOTO 1)
  23. - END
  24. #. Upon WARM Reset
  25. - SRC_GPR10 bit PERSIST_SECONDARY_BOOT is retained
  26. - if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 0
  27. - BootROM attempts to start bootloader A-copy
  28. - if A-copy valid
  29. - BootROM starts A-copy
  30. - END
  31. - if A-copy NOT valid
  32. - BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1
  33. - BootROM triggers WARM reset. GOTO 1.3)
  34. - END
  35. - if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 1
  36. - BootROM attempts to start bootloader B-copy
  37. - if B-copy valid
  38. - BootROM starts B-copy
  39. - END
  40. - if B-copy NOT valid
  41. - System hangs
  42. - END
  43. Setup
  44. -----
  45. The bootloader A-copy must be placed at predetermined offset in SD/eMMC. The
  46. bootloader B-copy area offset is determined by an offset stored in Secondary
  47. Image Table (SIT). The SIT must be placed at predetermined offset in SD/eMMC.
  48. The following table contains offset of SIT, bootloader A-copy and recommended
  49. bootloader B-copy offset. The offsets are in 512 Byte sector units (that is
  50. offset 0x1 means 512 Bytes from the start of SD/eMMC card data partition).
  51. For details on the addition of two numbers in recommended B-copy offset, see
  52. SIT format below.
  53. +----------+--------------------+-----------------------+-----------------------------+
  54. | SoC | SIT offset (fixed) | A-copy offset (fixed) | B-copy offset (recommended) |
  55. +----------+--------------------+-----------------------+-----------------------------+
  56. | iMX7D | 0x1 | 0x2 | 0x800+0x2 |
  57. +----------+--------------------+-----------------------+-----------------------------+
  58. | iMX8MM | 0x41 | 0x42 | 0x1000+0x42 |
  59. +----------+--------------------+-----------------------+-----------------------------+
  60. SIT format
  61. ~~~~~~~~~~
  62. SIT is a 20 byte long structure containing of 5 32-bit words. Those encode
  63. bootloader B-copy area offset (called "firstSectorNumber"), magic value
  64. (called "tag") that is always 0x00112233, and three unused words set to 0.
  65. SIT is documented in [1]_ and [2]_. Example SIT are below::
  66. $ hexdump -vC sit-mx7d.bin
  67. 00000000 00 00 00 00
  68. 00000004 00 00 00 00
  69. 00000008 33 22 11 00 <--- This is the "tag"
  70. 0000000c 00 08 00 00 <--- This is the "firstSectorNumber"
  71. 00000010 00 00 00 00
  72. $ hexdump -vC sit-mx8mm.bin
  73. 00000000 00 00 00 00
  74. 00000004 00 00 00 00
  75. 00000008 33 22 11 00 <--- This is the "tag"
  76. 0000000c 00 10 00 00 <--- This is the "firstSectorNumber"
  77. 00000010 00 00 00 00
  78. B-copy area offset ("firstSectorNumber") is offset, in units of 512 Byte
  79. sectors, that is added to the start of boot media when switching between
  80. A-copy and B-copy. For A-copy, this offset is 0x0. For B-copy, this offset
  81. is determined by SIT (e.g. if firstSectorNumber is 0x1000 as it is above
  82. in sit-mx8mm.bin, then the B-copy offset is 0x1000 sectors = 2 MiB).
  83. Bootloader A-copy (e.g. u-boot.imx or flash.bin) is placed at fixed offset
  84. from A-copy area offset (e.g. 0x2 sectors from sector 0x0 for iMX7D, which
  85. means u-boot.imx A-copy must be written to sector 0x2).
  86. The same applies to bootloader B-copy, which is placed at fixed offset from
  87. B-copy area offset determined by SIT (e.g. 0x2 sectors from sector 0x800 [see
  88. sit-mx7d.bin example above, this can be changed in SIT firstSectorNumber] for
  89. iMX7D, which means u-boot.imx B-copy must be written to sector 0x802)
  90. **WARNING:**
  91. B-copy area offset ("firstSectorNumber") is NOT equal to bootloader
  92. (image, which is u-boot.imx or flash.bin) B-copy offset.
  93. To generate SIT, use for example the following bourne shell printf command::
  94. $ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x08\x00\x00\x0\x0\x0\x0' > sit-mx7d.bin
  95. $ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x10\x00\x00\x0\x0\x0\x0' > sit-mx8mm.bin
  96. Write bootloader A/B copy and SIT to SD/eMMC
  97. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  98. Examples of writing SIT and two copies of bootloader to SD or eMMC:
  99. - iMX8MM, SD card at /dev/sdX, Linux command line
  100. ::
  101. $ dd if=sit-mx8mm.bin of=/dev/sdX bs=512 seek=65
  102. $ dd if=flash.bin of=/dev/sdX bs=512 seek=66
  103. $ dd if=flash.bin of=/dev/sdX bs=512 seek=4162
  104. - iMX8MM, eMMC 1 data partition, U-Boot command line
  105. ::
  106. => mmc partconf 1 0 0 0
  107. => dhcp ${loadaddr} sit-mx8mm.bin
  108. => mmc dev 1
  109. => mmc write ${loadaddr} 0x41 0x1
  110. => dhcp ${loadaddr} flash.bin
  111. => setexpr blkcnt ${filesize} + 0x1ff && setexpr blkcnt ${blkcnt} / 0x200
  112. => mmc dev 1
  113. => mmc write ${loadaddr} 0x42 ${blkcnt}
  114. => mmc write ${loadaddr} 0x1042 ${blkcnt}
  115. WARM reset into B-copy using WDT
  116. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  117. To perform a reboot into B-copy, the PERSIST_SECONDARY_BOOT must be set
  118. in SRC_GPR0 register. Example on iMX8MM::
  119. => mw 0x30390098 0x40000000
  120. A WARM reset can be triggered using WDT as follows::
  121. => mw.w 0x30280000 0x25
  122. References
  123. ----------
  124. .. [1] i.MX 7Dual Applications Processor Reference Manual, Rev. 1, 01/2018 ; section 6.6.5.3.5 Redundant boot support for expansion device
  125. .. [2] i.MX 8M Mini Applications Processor Reference Manual, Rev. 3, 11/2020 ; section 6.1.5.4.5 Redundant boot support for expansion device