littlefs VS uf2

Pointers correctly round-trip through unrelated pointer types, provided the alignment for both types is compatible.

At least one bit does look a bit questionable: lfs_mlist is treated as the common initial sequence of lfs_dir and lfs_file, even though it isn't, and common initial sequences only apply to union fields anyway. Example cast of struct dir * to struct lfs_mlist * (probably valid of itself, assuming the alignment is compatible): https://github.com/littlefs-project/littlefs/blob/c733d9ec57... then use struct dir as if it were actually a struct lfs_mlist: https://github.com/littlefs-project/littlefs/blob/c733d9ec57...

(There's other occurrences of the same kind of thing.)

Strictly speaking, I think this might be unfixable without a bunch of work, but so much stuff does this kind of operation that any compiler that doesn't do what you expect will have been fixed by now. (Assuming you're not one of those people who is going to pop up and tell us with a straight face that what we should expect is for the compiler to do absolutely anything - except, perhaps, for having it generate correct code, which would be defective behaviour that should be eliminated.) Maybe improve the odds by using lfs_mlist as the common initial sequence of both structs, and fingers crossed that the compiler considers the union rules to apply to this case too. Or compile with -fno-strict-aliasing.

Also, it looks like you're writing to the flash every second the engine is running. Do you have an idea of what the endurance of that might be? I'm not too familiar with this but supposedly the flash on the Pico is good for at least 100K program/erase cycles and Micropython uses LittleFS on RP2040 which does wear leveling. I looked for more official info and the rp2 port code backs that up with a note: "the flash requires the programming size to be aligned to 256 bytes". And the littlefs readme does say it does wear leveling and other good stuff.

Maybe first go and localize which assumption has been voided, i.e. what of the many places in littlefs that raise this error actually raise it? And... erm... what littlefs are you talking about? https://github.com/littlefs-project/littlefs doesn't seem to have a fs_close() function...

Rather easy to add LittleFS for file storage onto the NOR flash. https://github.com/littlefs-project/littlefs

And the UF2 reference from Microsoft: https://github.com/microsoft/uf2/blob/master/README.md

I'm compiling a very stripped down example from https://github.com/embassy-rs/nrf-softdevice that should just loop forever and turn an LED on and off. I convert from a binary to the uf2 using this script linked in the adafruit bootloader repository. The command I run is uf2conv.py -c -b 0x26000 -f 0xADA52840. When running file on my binary the output is UF2 firmware image, family Nordic NRF52840, address 0x026000, 42 total blocks, exactly the same as on the ZMK image that works without a problem.

How can I (someone with no electronics or programming experience) configure my own layout using QMK Config and then compile it into a .uf2 file that works on the Sea-Picro with my Ferris Sweep?

In case you haven't seen the UF2 file format, it's specifically designed to be robust w.r.t ensuring that the content makes it to the target intact despite common OS quirks.

https://github.com/microsoft/uf2

  - Data is divided into 512 byte blocks, which lines up with the mass storage transfer size.

The bootloader uses the UF2 protocol, which is cleverly designed to allow "drag and drop" flashing over USB mass storage.

I'd strongly recommend using an application-specific USB bootloader if possible. The UF2 firmware update protocol is particularly slick, as it allows users to upload new firmware over USB mass storage and requires no staging space; if using this is an option, I'd go for it.

The mentioned UF2 standard (UF2 - mdf5 checksum) actually offers the option to specifiy an MD5 checksum. Which is heavier on resources.