613: Rust stable support r=Dirbaio a=Dirbaio
This PR adds (limited) stable Rust support!
The drawbacks are:
- No `#[embassy::task]`, `#[embassy::main]`. (requires `type_alias_impl_trait`). You have to manually allocate the tasks somewhere they'll live forever. See [example](https://github.com/embassy-rs/embassy/blob/master/examples/nrf/src/bin/raw_spawn.rs)
- No async trait impls (requires GATs). Note that the full API surface of HALs is still available through inherent methods: #552#581
- Some stuff is not constructible in const (requires `const_fn_trait_bound`), although there's an (ugly) workaround for the generic `Mutex`.
So it's not that bad in the end, it's fully usable for shipping production-ready firmwares. We'll still recommend nightly as the default, until GATs and `type_alias_impl_trait` are stable.
Co-authored-by: Dario Nieuwenhuis <dirbaio@dirbaio.net>
This commit allows event_endtx to be used outside of the Uarte itself. As a consequence, PPI can be used to drive tasks given the end of transmission on the Uarte. This is particularly useful for situations like RS485 where a GPIO must be set to high when transmitting then cleared when done. A non-ppi approach can cause a delay in the clearing of this GPIO as other Embassy tasks might become scheduled.
A new `split` method is introduced such that the Uarte tx and rx can be used from separate tasks. An MPSC is used to illustrate how data may be passed between these tasks.
The constructors themselves are not strictly unsafe. Interactions with DMA can be generally unsafe if a future is dropped, but that's a separate issue. It is important that we use the `unsafe` keyword diligently as it can lead to confusion otherwise.
- Scary pointer math is now contained in the tasks and events
- ppi now sets the tasks and events immediately and the struct is now zero-sized
- StaticToOne is renamed to ZeroToOne
- Used DPPI tasks and events now panic when enabled twice
- Removed ConfigurableChannel and added capacity numbers to the channels
- Replaced the PPI api with a new one using the DPPI terminology (publish & subscribe)
- Updated all tasks and event registers for DPPI
- It disturbs other stuff that uses WFE/SEV in the system. I ran into
issues with this.
- It needs the irq handler to check for RXTO/TXSTOPPED errors, which makes
it slower.
Add type UarteWithIdle that implements Read, Write and ReadUntilIdle
traits. The type uses a timer + 2 PPI channels internally, triggered on
RTXSTARTED event.
