Multiple bin/elf files to single UF2 file

[maxgerhardt]

In reference to maxgerhardt/platform-raspberrypi#108.

Currently, the picotool does not support giving it multiple input files (and input filetypes and possible offsets) in the picotool convert convert command, only a single one.

I have the situation that I build a firmware.elf (firmware code) and a littelfs.bin (filesystem to be placed at 0x1037f000 in flash). I would like to combine both of those into a single UF2 image.

The tool does not support that.

However, in reference to the UF2 filesystem specification (https://github.com/microsoft/uf2/tree/d03b585ed780ed51bb0d1e6e8cf233aacb408305?tab=readme-ov-file#file-format), a UF2 file is simple a concatination of 512 byte blocks, each block having its target flash addresses embedded. As thus, I would expect if I concatenate two UF2 files, it will simply write all blocks of that UF2 file.

But, when I try to use

picotool uf2 convert "firmware.elf" "firmware.uf2"
picotool uf2 convert "littlefs.bin" "littlefs.uf2" --offset 0x1037f000
copy /b firmware.uf2+littlefs.uf2 firmware_with_fs.uf2

And I drag and drop that UF2 file to the pico's boot drive, the file copy simply stops after a short while (I assume after it copied the firmware part) and then resets, not accepting the filesystem part. An error about copying to a non-existing device occurs.

When I upload the file via picotool, it uploads and works, showing two loading processes.

picotool.exe load -v -x "C:\Users\Max\.platformio\platforms\raspberrypi\examples\arduino-littlefs\.pio\build\rpipico2\firmware_with_fs.uf2"
Family id 'rp2350-arm-s' can be downloaded in absolute space:
  00000000->02000000
Loading into Flash: [==============================]  100%
Loading into Flash: [==============================]  100%
Verifying Flash:    [==============================]  100%
  OK
Verifying Flash:    [==============================]  100%
  OK

The device was rebooted to start the application.

The application then works.

------ Reading file1.txt -------
Hello!

Welcome to the Raspberry Pi Pico using arduino-pico!
------ file read successfully -------

How can I create a UF2 using picotool that is accepted by the BOOTSEL drive / MSC loader of a RP2350 and RP2040?

uf2_examples.zip

[maxgerhardt]

Switching the order of the copy command so that the filesystem goes first, then the firmware, causes the file to uploadable by the BOOTSEL drive. But then the firmware does not find the filesystem, suggesting it was not properly copied.

------ Reading file1.txt -------
file1.txt not found

All tests were done with uploading flash_nuke.uf2 beforehand to ensure a clean state.

[lurch]

Sounds similar to #169 (and the other linked issues in there) ?

[will-v-pi]

As thus, I would expect if I concatenate two UF2 files, it will simply write all blocks of that UF2 file.

Note that the reason this doesn't happen is the bootrom will reboot after it's received a full UF2 file (ie the sequential block number equals the total number of blocks), so will not write the second UF2 file - to make it write both you need to change the UF2 block numbers when joining the files together

Alternatively on RP2350, you can use partitions and make use of no_reboot_on_uf2_download to not reboot after the filesystem is copied into the partition, and only reboot once the firmware has been copied

[maxgerhardt]

Thanks, that was it. I wrote a simple Python function that rewrites two UF2 files to be one UF2 file with monotonically increasing block numbers, using the combined total number of blocks and taking care to use the familyID from the UF2 file containing the firmware (if they differ in the same UF2 file, the bootloader rejects it.)

maxgerhardt/platform-raspberrypi@f824705