bootloaders/riotboot_vfs: add VFS based bootloader

[benpicco]

Contribution description

Often it's not feasible to partition the internal flash into two halves simple because the required firmware is too large for just half of the flash. With the current chip shortage larger chips are not always available (if such parts even exist).

If the board has an external flash with a filesystem, we can store the new firmware there and use riotboot to transfer it to the internal flash.

Before flashing the new firmware, we make a backup of the current one so that the board can recover on it's own in case of a bad firmware. (In a follow-up we can add a watchdog timer to do an automated reboot if the new firmware does not clear it in time).

The path to firmware file to flash is stored in a do_update file as text. Once the firmware is flashed, the file contains the path of the backup firmware. It is the job of the new firmware to remove this file, otherwise the backup is applied on reboot.

Testing procedure

I have not figured out how to create a combined image yet and whenever I flash the application firmware the bootloader also gets erased. So whenever you flash the application, you also have to flash the bootloader:

• flash tests/riotboot_vfs on a board with external storage
• flash bootloaders/riotboot_vfs

Now on the shell, save the current firmware with dump_rom /nvm0/test.bin
You can re-flash the current firmware with flash_rom /nvm0/test.bin

same54-xpro

2022-03-22 12:51:37,456 # riotboot VFS
2022-03-22 12:51:37,466 # jump to 0xa000
2022-03-22 12:51:37,505 # main(): This is RIOT! (Version: 2022.04-devel-924-g0f6a3-bootloaders/riotboot_vfs)
> dump_rom /nvm/image.bin
2022-03-22 12:53:29,692 # wrote 57344 bytes to /nvm/image.bin
> flash_rom /nvm/image.bin
2022-03-22 12:53:36,727 # riotboot VFS
2022-03-22 12:53:36,742 # flashing /nvm/image.bin…
2022-03-22 12:53:40,027 # erase page 5
2022-03-22 12:53:40,070 # erase page 6
2022-03-22 12:53:40,114 # erase page 7
2022-03-22 12:53:40,155 # erase page 8
2022-03-22 12:53:40,198 # erase page 9
2022-03-22 12:53:40,240 # erase page 10
2022-03-22 12:53:40,283 # erase page 11
2022-03-22 12:53:40,324 # erase page 12
2022-03-22 12:53:40,367 # write 57344 bytes
2022-03-22 12:53:40,561 # done.
2022-03-22 12:53:40,562 # jump to 0xa000
2022-03-22 12:53:40,609 # main(): This is RIOT! (Version: 2022.04-devel-924-g0f6a3-bootloaders/riotboot_vfs)
ls /nvm
2022-03-22 12:54:14,020 # ls /nvm
2022-03-22 12:54:14,022 # ./
2022-03-22 12:54:14,023 # ../
2022-03-22 12:54:14,033 # fdb_kvdb1/
2022-03-22 12:54:14,042 # fdb_tsdb1/
2022-03-22 12:54:14,050 # image.bin	57344 B
2022-03-22 12:54:14,056 # old_image.bin	52224 B
2022-03-22 12:54:14,057 # total 2 files

nrf52840dk

Flash a modified image and store it on the flash

2022-05-17 20:16:22,869 # main(): This is RIOT! (Version: 2022.07-devel-460-g0a82d-bootloaders/riotboot_vfs)
2022-05-17 20:16:22,871 # riotboot VFS example
2022-05-17 20:16:22,873 #  > With Modifications! <

2022-05-17 20:16:43,974 # > dump_rom /nvm0/modi.bin
2022-05-17 20:16:45,781 # wrote 49152 bytes to /nvm0/modi.bin

Flash the vanilla image again and load the modified image from external Flash

2022-05-17 20:17:05,556 # main(): This is RIOT! (Version: 2022.07-devel-460-g0a82d-bootloaders/riotboot_vfs)
2022-05-17 20:17:05,558 # riotboot VFS example

2022-05-17 20:17:11,238 # > flash_rom /nvm0/modi.bin
2022-05-17 20:17:14,730 # main(): This is RIOT! (Version: 2022.07-devel-460-g0a82d-bootloaders/riotboot_vfs)
2022-05-17 20:17:14,732 # riotboot VFS example
2022-05-17 20:17:14,734 #  > With Modifications! <

Issues/PRs references

depends on and includes #17341

[fjmolinas]

@benpicco Could you split out all the unrelated commits as well as document the added vfs/riotboot functions?