| i.MX7D/i.MX8MM SRC_GPR10 PERSIST_SECONDARY_BOOT for bootloader A/B switching |
| ============================================================================ |
| |
| Introduction |
| ------------ |
| Since at least iMX53 until iMX8MM, it is possible to have two copies of |
| bootloader in SD/eMMC and switch between them. The switch is triggered |
| either by the BootROM in case the bootloader image is faulty OR can be |
| enforced by the user. |
| |
| Operation |
| --------- |
| #. Upon Power-On Reset (POR) |
| |
| - SRC_GPR10 bit PERSIST_SECONDARY_BOOT is set to 0 |
| - BootROM attempts to start bootloader A-copy |
| |
| - if A-copy valid |
| |
| - BootROM starts A-copy |
| - END |
| |
| - if A-copy NOT valid |
| |
| - BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1 |
| - BootROM triggers WARM reset, GOTO 1) |
| - END |
| |
| #. Upon COLD Reset |
| |
| - GOTO 1) |
| - END |
| |
| #. Upon WARM Reset |
| |
| - SRC_GPR10 bit PERSIST_SECONDARY_BOOT is retained |
| |
| - if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 0 |
| |
| - BootROM attempts to start bootloader A-copy |
| |
| - if A-copy valid |
| |
| - BootROM starts A-copy |
| - END |
| |
| - if A-copy NOT valid |
| |
| - BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1 |
| - BootROM triggers WARM reset. GOTO 1.3) |
| - END |
| |
| - if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 1 |
| |
| - BootROM attempts to start bootloader B-copy |
| |
| - if B-copy valid |
| |
| - BootROM starts B-copy |
| - END |
| |
| - if B-copy NOT valid |
| - System hangs |
| - END |
| |
| Setup |
| ----- |
| The bootloader A-copy must be placed at predetermined offset in SD/eMMC. The |
| bootloader B-copy area offset is determined by an offset stored in Secondary |
| Image Table (SIT). The SIT must be placed at predetermined offset in SD/eMMC. |
| |
| The following table contains offset of SIT, bootloader A-copy and recommended |
| bootloader B-copy offset. The offsets are in 512 Byte sector units (that is |
| offset 0x1 means 512 Bytes from the start of SD/eMMC card data partition). |
| For details on the addition of two numbers in recommended B-copy offset, see |
| SIT format below. |
| |
| +----------+-----------------------------+--------------------+-----------------------+-----------------------------+ |
| | SoC | Boot Device Type | SIT offset (fixed) | A-copy offset (fixed) | B-copy offset (recommended) | |
| +----------+-----------------------------+--------------------+-----------------------+-----------------------------+ |
| | iMX7D | | 0x1 | 0x2 | 0x800+0x2 | |
| +----------+-----------------------------+--------------------+-----------------------+-----------------------------+ |
| | iMX8MM | SD/eSD/MMC/eMMC normal boot | 0x41 | 0x42 | 0x1000+0x42 | |
| +----------+-----------------------------+--------------------+-----------------------+-----------------------------+ |
| | iMX8MM | eMMC Fast boot fuse blown | 0x1 | 0x2 | 0x1000+0x2 | |
| +----------+-----------------------------+--------------------+-----------------------+-----------------------------+ |
| |
| SIT format |
| ~~~~~~~~~~ |
| SIT is a 20 byte long structure containing of 5 32-bit words. Those encode |
| bootloader B-copy area offset (called "firstSectorNumber"), magic value |
| (called "tag") that is always 0x00112233, and three unused words set to 0. |
| SIT is documented in [1]_ and [2]_. Example SIT are below:: |
| |
| $ hexdump -vC sit-mx7d.bin |
| 00000000 00 00 00 00 |
| 00000004 00 00 00 00 |
| 00000008 33 22 11 00 <--- This is the "tag" |
| 0000000c 00 08 00 00 <--- This is the "firstSectorNumber" |
| 00000010 00 00 00 00 |
| |
| $ hexdump -vC sit-mx8mm.bin |
| 00000000 00 00 00 00 |
| 00000004 00 00 00 00 |
| 00000008 33 22 11 00 <--- This is the "tag" |
| 0000000c 00 10 00 00 <--- This is the "firstSectorNumber" |
| 00000010 00 00 00 00 |
| |
| B-copy area offset ("firstSectorNumber") is offset, in units of 512 Byte |
| sectors, that is added to the start of boot media when switching between |
| A-copy and B-copy. For A-copy, this offset is 0x0. For B-copy, this offset |
| is determined by SIT (e.g. if firstSectorNumber is 0x1000 as it is above |
| in sit-mx8mm.bin, then the B-copy offset is 0x1000 sectors = 2 MiB). |
| |
| Bootloader A-copy (e.g. u-boot.imx or flash.bin) is placed at fixed offset |
| from A-copy area offset (e.g. 0x2 sectors from sector 0x0 for iMX7D, which |
| means u-boot.imx A-copy must be written to sector 0x2). |
| |
| The same applies to bootloader B-copy, which is placed at fixed offset from |
| B-copy area offset determined by SIT (e.g. 0x2 sectors from sector 0x800 [see |
| sit-mx7d.bin example above, this can be changed in SIT firstSectorNumber] for |
| iMX7D, which means u-boot.imx B-copy must be written to sector 0x802) |
| |
| **WARNING:** |
| B-copy area offset ("firstSectorNumber") is NOT equal to bootloader |
| (image, which is u-boot.imx or flash.bin) B-copy offset. |
| |
| To generate SIT, use for example the following bourne shell printf command:: |
| |
| $ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x08\x00\x00\x0\x0\x0\x0' > sit-mx7d.bin |
| $ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x10\x00\x00\x0\x0\x0\x0' > sit-mx8mm.bin |
| |
| Write bootloader A/B copy and SIT to SD/eMMC |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Examples of writing SIT and two copies of bootloader to SD or eMMC: |
| |
| - iMX8MM, SD card at /dev/sdX, Linux command line |
| :: |
| |
| $ dd if=sit-mx8mm.bin of=/dev/sdX bs=512 seek=65 |
| $ dd if=flash.bin of=/dev/sdX bs=512 seek=66 |
| $ dd if=flash.bin of=/dev/sdX bs=512 seek=4162 |
| |
| - iMX8MM, eMMC 1 data partition, U-Boot command line |
| :: |
| |
| => mmc partconf 1 0 0 0 |
| |
| => dhcp ${loadaddr} sit-mx8mm.bin |
| => mmc dev 1 |
| => mmc write ${loadaddr} 0x41 0x1 |
| |
| => dhcp ${loadaddr} flash.bin |
| => setexpr blkcnt ${filesize} + 0x1ff && setexpr blkcnt ${blkcnt} / 0x200 |
| => mmc dev 1 |
| => mmc write ${loadaddr} 0x42 ${blkcnt} |
| => mmc write ${loadaddr} 0x1042 ${blkcnt} |
| |
| WARM reset into B-copy using WDT |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| To perform a reboot into B-copy, the PERSIST_SECONDARY_BOOT must be set |
| in SRC_GPR10 register. Example on iMX8MM:: |
| |
| => mw 0x30390098 0x40000000 |
| |
| A WARM reset can be triggered using WDT as follows:: |
| |
| => mw.w 0x30280000 0x25 |
| |
| References |
| ---------- |
| |
| .. [1] i.MX 7Dual Applications Processor Reference Manual, Rev. 1, 01/2018 ; section 6.6.5.3.5 Redundant boot support for expansion device |
| .. [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 |
