Add support for RP2350 aka Raspberry Pi Pico 2

[thenewwazoo]

This change adds very, very basic support for the Raspberry Pi Pico 2's RP2350 chip and its 4 MiB onboard flash. A new demo app is added with only jefe and idle tasks. This is mostly intended as a basis for discussion of #2200.

Nonetheless, it runs and passes tests!

$ cargo xtask humility app/demo-pi-pico-2/app.toml -- tasks
    Finished `dev` profile [optimized + debuginfo] target(s) in 0.13s
     Running `target/debug/xtask humility app/demo-pi-pico-2/app.toml -- tasks`
humility: attached via CMSIS-DAP
system time = 859044
ID TASK                       GEN PRI STATE
 0 jefe                         0   0 recv, notif: fault timer(T+56)
 1 idle                         0   5 RUNNING

NOTE that this is intended to pair with an as-yet-unsubmitted update to humility, the status of which is likely uncertain.

Additional minor tweaks include:

• some error reporting when files can't be found (emitting the sought filename)
• emitting a firmware map in the dist directory

[aapoalas]

Left a couple of comments from an outsider.

IMO this is pretty damn cool, and I'll try take this for a spin if I get the time.

Great stuff getting Hubris working on RPi <3 !

[aapoalas]

suggestion: This seems like it should rather be a repr(C) struct with named fields instead of an array with commented indexes.

nitpick: I'd personally go with usize types since these seem to be addresses, though the Hubris codebase does use u32 for addresses very often. It makes sense in the APIs but (IMO) less so inside the services / tasks.

[thenewwazoo]

I agree, this should eventually be a repr(C) struct since it encodes fields with values and flags (in 5.9.3.1). For now I've gone with the raw bytes described in the datasheet (5.9.5.1) since it's an MVP and I'm not even sure Oxide wants this in their repo 😆 If I get any sort of encouragement from them, I expect I'll expand on this and other aspects of the PR.

As for u32 vs usize, in the ultimate structure, it'd be a mix of types, with u8/u16/u32 for values and usize for the address, as noted. For now, it's just u32 bytes straight out of the datasheet.

[thenewwazoo]

Left a couple of comments from an outsider.

IMO this is pretty damn cool, and I'll try take this for a spin if I get the time.

Great stuff getting Hubris working on RPi <3 !

Thank you! Please note that I got this working alongside an update to humility that is required for it to work, and which is its own ball of wax.

Your suggestion for exhubris is well-heard, and I'm sorry for not responding earlier. I was... focused... on getting hubris booting. I like the idea and goals of exhubris, but it is quite a different product with a different learning curve, and its future and relationship with hubris itself isn't entirely clear (authorship notwithstanding). I decided to just EAFP and see how it went.

[aapoalas]

Your suggestion for exhubris is well-heard, and I'm sorry for not responding earlier. I was... focused... on getting hubris booting. I like the idea and goals of exhubris, but it is quite a different product with a different learning curve, and its future and relationship with hubris itself isn't entirely clear (authorship notwithstanding). I decided to just EAFP and see how it went.

Sorry for being vocal about it as well. I removed the section about it in the above comment (as you of course noticed) because after posting it I realised it's not really my place to try tell you what to do. Let's hope this gets some bandwidth from the Oxide folks! :)