Add a sample to read the partition table

[oyama]

Add a sample that reads the partition table from runtime.

I would appreciate comments on the partition table operation procedure itself, as I did not know the correct way to do it and coded it by trial and error.

[lurch]

@oyama You might find some useful partition-related code in https://github.com/raspberrypi/picotool ? 🤷‍♂️

[oyama]

@lurch Thank you for the pointer! It looks like the relevant code is around here: https://github.com/raspberrypi/picotool/blob/de8ae5ac334e1126993f72a5c67949712fd1e1a4/bintool/metadata.h#L227 – I'll take a look.
However, my goal is to implement a file system that respects both partitions and permissions, so it seems I'll also need to create a separate read/write example using rom_flash_op().

[will-v-pi]

A few comments from a first pass reviewing this

[oyama]

Based on the comments, the read process of the partition table was divided and organized into a fixed-length field portion and a variable-length field portion.

[will-v-pi]

LGTM, just a few minor things

[oyama]

Thanks suggestions. Very helpful.

[lurch]

@will-v-pi Is it worth hoisting any of these defines into pico-sdk, or is it fine for each project to define them itself?

[will-v-pi]

It'll probably be sensible to add them to picobin.h, along with more partition table handling in bootrom.c - @kilograham might have opinions too?

[lurch]

@oyama I'd just like to say thank you very much for putting up with all my niggly comments. I sometimes get a bit carried away when reviewing code 😆

[oyama]

@lurch Thank you so much for your detailed feedback, it was incredibly helpful and inspiring. I truly appreciate your attention to every little detail, and your comments have motivated me to improve further. Thanks again for your support!

[lurch]

Now that you've added all the code to display extra family IDs, perhaps it's worth exercising that code by putting an extra family ID in your pt.json ? 🤔

[lurch]

Similarly to how you have a function (uf2_family_ids_join) for creating the formatted family-ids string, I wonder if it might be worth pulling out a separate function for creating the S(%s%s) NSBOOT(%s%s) NS(%s%s) part of this string? (which I believe you could then also use in the per-partition loop?) 🤔

[lurch]

Haha, I was about to suggest that you could use %c instead of %s in your printf formatting, but then I realised that you can't do "empty string" when using char 😂