feat: add basic support for nRF51 chips to embassy-nrf

[lulf]

TODO:

• HIL test
• Docs update
• More peripherals (can be added on demand later I would say)

@Dirbaio would you be able to hook your nrf51-dk into the HIL setup? My own dk is fried, but I verified code is running on my microbit v1.

[Dirbaio]

I think we could (should?) avoid adding the dependency on portable-atomic,

• RNG could use a Mutex<RefCell<State>> (and change the AtomicWaker to a WakerRegistration). It'd be faster because if you modify multiple fields it'll acquire a single CS, not one for each field.
• The time driver already does a CS for next_period so we can do "read, modify, write" manually which needs no CAS. stm32 already does this.

[Dirbaio]

added nrf51-dk to HIL rig. Wire connected between P0.13 and P0.14 for GPIO etc testing.

[lulf]

@Dirbaio Thanks! I'll add a HIL test as well as addressing the comments soon!

[lulf]

bender run

[lulf]

@Dirbaio Two issues remaining:

• Running from RAM doesn't work, it looks related to the size and the available RAM because a simple test that doesn't do gpio or timer runs fine from RAM.
• I've set it to run from flash, which works locally, but fails with ERROR - Run failed: Flash content verification failed. I'm not entirely sure why this is only happening on CI.

[Dirbaio]

Running from RAM doesn't work, it looks related to the size and the available RAM because a simple test that doesn't do gpio or timer runs fine from RAM.

that's fine. we already have some stm32's that do HIL from flash because not enough RAM too...

I've set it to run from flash, which works locally, but fails with ERROR - Run failed: Flash content verification failed. I'm not entirely sure why this is only happening on CI.

Fixed in probe-rs/probe-rs#2119

bender run

[Dirbaio]

duh of course it doesn't work if I don't put back the nrf51-dk in the HL rig.

bender run

[Dirbaio]

thank you! 🥳