175 lines
6.0 KiB
ReStructuredText
175 lines
6.0 KiB
ReStructuredText
i.MX7D/i.MX8MM SRC_GPR10 PERSIST_SECONDARY_BOOT for bootloader A/B switching
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============================================================================
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Introduction
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------------
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Since at least iMX53 until iMX8MM, it is possible to have two copies of
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bootloader in SD/eMMC and switch between them. The switch is triggered
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either by the BootROM in case the bootloader image is faulty OR can be
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enforced by the user.
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Operation
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---------
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#. Upon Power-On Reset (POR)
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- SRC_GPR10 bit PERSIST_SECONDARY_BOOT is set to 0
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- BootROM attempts to start bootloader A-copy
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- if A-copy valid
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- BootROM starts A-copy
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- END
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- if A-copy NOT valid
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- BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1
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- BootROM triggers WARM reset, GOTO 1)
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- END
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#. Upon COLD Reset
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- GOTO 1)
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- END
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#. Upon WARM Reset
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- SRC_GPR10 bit PERSIST_SECONDARY_BOOT is retained
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- if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 0
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- BootROM attempts to start bootloader A-copy
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- if A-copy valid
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- BootROM starts A-copy
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- END
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- if A-copy NOT valid
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- BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1
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- BootROM triggers WARM reset. GOTO 1.3)
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- END
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- if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 1
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- BootROM attempts to start bootloader B-copy
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- if B-copy valid
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- BootROM starts B-copy
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- END
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- if B-copy NOT valid
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- System hangs
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- END
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Setup
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-----
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The bootloader A-copy must be placed at predetermined offset in SD/eMMC. The
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bootloader B-copy area offset is determined by an offset stored in Secondary
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Image Table (SIT). The SIT must be placed at predetermined offset in SD/eMMC.
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The following table contains offset of SIT, bootloader A-copy and recommended
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bootloader B-copy offset. The offsets are in 512 Byte sector units (that is
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offset 0x1 means 512 Bytes from the start of SD/eMMC card data partition).
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For details on the addition of two numbers in recommended B-copy offset, see
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SIT format below.
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+----------+--------------------+-----------------------+-----------------------------+
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| SoC | SIT offset (fixed) | A-copy offset (fixed) | B-copy offset (recommended) |
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+----------+--------------------+-----------------------+-----------------------------+
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| iMX7D | 0x1 | 0x2 | 0x800+0x2 |
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+----------+--------------------+-----------------------+-----------------------------+
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| iMX8MM | 0x41 | 0x42 | 0x1000+0x42 |
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+----------+--------------------+-----------------------+-----------------------------+
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SIT format
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~~~~~~~~~~
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SIT is a 20 byte long structure containing of 5 32-bit words. Those encode
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bootloader B-copy area offset (called "firstSectorNumber"), magic value
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(called "tag") that is always 0x00112233, and three unused words set to 0.
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SIT is documented in [1] and [2]. Example SIT are below::
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$ hexdump -vC sit-mx7d.bin
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00000000 00 00 00 00
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00000004 00 00 00 00
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00000008 33 22 11 00 <--- This is the "tag"
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0000000c 00 08 00 00 <--- This is the "firstSectorNumber"
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00000010 00 00 00 00
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$ hexdump -vC sit-mx8mm.bin
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00000000 00 00 00 00
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00000004 00 00 00 00
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00000008 33 22 11 00 <--- This is the "tag"
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0000000c 00 10 00 00 <--- This is the "firstSectorNumber"
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00000010 00 00 00 00
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B-copy area offset ("firstSectorNumber") is offset, in units of 512 Byte
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sectors, that is added to the start of boot media when switching between
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A-copy and B-copy. For A-copy, this offset is 0x0. For B-copy, this offset
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is determined by SIT (e.g. if firstSectorNumber is 0x1000 as it is above
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in sit-mx8mm.bin, then the B-copy offset is 0x1000 sectors = 2 MiB).
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Bootloader A-copy (e.g. u-boot.imx or flash.bin) is placed at fixed offset
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from A-copy area offset (e.g. 0x2 sectors from sector 0x0 for iMX7D, which
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means u-boot.imx A-copy must be written to sector 0x2).
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The same applies to bootloader B-copy, which is placed at fixed offset from
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B-copy area offset determined by SIT (e.g. 0x2 sectors from sector 0x800 [see
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sit-mx7d.bin example above, this can be changed in SIT firstSectorNumber] for
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iMX7D, which means u-boot.imx B-copy must be written to sector 0x802)
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**WARNING:**
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B-copy area offset ("firstSectorNumber") is NOT equal to bootloader
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(image, which is u-boot.imx or flash.bin) B-copy offset.
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To generate SIT, use for example the following bourne shell printf command::
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$ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x08\x00\x00\x0\x0\x0\x0' > sit-mx7d.bin
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$ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x10\x00\x00\x0\x0\x0\x0' > sit-mx8mm.bin
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Write bootloader A/B copy and SIT to SD/eMMC
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Examples of writing SIT and two copies of bootloader to SD or eMMC:
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- iMX8MM, SD card at /dev/sdX, Linux command line
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::
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$ dd if=sit-mx8mm.bin of=/dev/sdX bs=512 seek=65
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$ dd if=flash.bin of=/dev/sdX bs=512 seek=66
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$ dd if=flash.bin of=/dev/sdX bs=512 seek=4162
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- iMX8MM, eMMC 1 data partition, U-Boot command line
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::
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=> mmc partconf 1 0 0 0
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=> dhcp ${loadaddr} sit-mx8mm.bin
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=> mmc dev 1
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=> mmc write ${loadaddr} 0x41 0x1
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=> dhcp ${loadaddr} flash.bin
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=> setexpr blkcnt ${filesize} + 0x1ff && setexpr blkcnt
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=> mmc dev 1
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=> mmc write ${loadaddr} 0x42 ${blkcnt}
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=> mmc write ${loadaddr} 0x1042 ${blkcnt}
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WARM reset into B-copy using WDT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To perform a reboot into B-copy, the PERSIST_SECONDARY_BOOT must be set
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in SRC_GPR0 register. Example on iMX8MM::
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=> mw 0x30390098 0x40000000
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A WARM reset can be triggered using WDT as follows::
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=> mw.w 0x30280000 0x25
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References
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----------
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.. [1] i.MX 7Dual Applications Processor Reference Manual, Rev. 1, 01/2018 ; section 6.6.5.3.5 Redundant boot support for expansion device
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.. [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
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