As per Tokio and others, this commit provides a `poll_flush` method on `AsyncWrite` so that a best-effort attempt at wakening once all bytes are flushed can be made.
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
Since `PeripheralMutex` is the only way to safely maintain state across interrupts, and it no longer allows setting the interrupt's priority, the priority changing isn't a concern.
This also prevents other causes of UB due to the interrupt being exposed during `with`, and allowing enabling the interrupt and setting its context to a bogus pointer.
`Peripheral` assumed that interrupts can't be preempted,
when they can be preempted by higher priority interrupts.
So I put the interrupt handler inside a critical section,
and also added checks for whether the state had been dropped
before the critical section was entered.
I also added a `'static` bound to `PeripheralState`,
since `Pin` only guarantees that the memory it directly references
will not be invalidated.
It doesn't guarantee that memory its pointee references also won't be invalidated.
There were already some implementations of `PeripheralState`
that weren't `'static`, though,
so I added an unsafe `PeripheralStateUnchecked` trait
and forwarded the `unsafe` to the constructors of the implementors.
The `interrupt` package previously tried to be drop-in compatible with the
`interrupt` package from PACs. THis meant that there was both a PAC-style enum
value `UARTE0` and an embassy-style owned `UARTE0Interrupt` type. This made
things VERY confusing.
This drops compatibility with the PAC, improving the names for embassy interrupts.
