- Move typelevel interrupts to a special-purpose mod: `embassy_xx::interrupt::typelevel`.
- Reexport the PAC interrupt enum in `embassy_xx::interrupt`.
This has a few advantages:
- The `embassy_xx::interrupt` module is now more "standard".
- It works with `cortex-m` functions for manipulating interrupts, for example.
- It works with RTIC.
- the interrupt enum allows holding value that can be "any interrupt at runtime", this can't be done with typelevel irqs.
- When "const-generics on enums" is stable, we can remove the typelevel interrupts without disruptive changes to `embassy_xx::interrupt`.
this reports errors at the same location the blocking uart would, which
works out to being mostly exact (except in the case of overruns, where
one extra character is dropped). this is actually easier than going
nuclear in the case of errors and nuking both the buffer contents and
the rx fifo, both of which are things we'd have to do in addition to
what's added here, and neither are needed for correctness.
sending break conditions is necessary to implement some protocols, and
the hardware supports this natively. we do have to make sure that we
don't assert a break condition while the uart is busy though, otherwise
the break may be inserted before the last character in the tx fifo.
* Only clear interrupt flags that have fired (so that we do not lose any error flags)
* Enable RX interrupt when a read is requested, disable it when the RX buffer is full
* Rework TX interrupt handling: its "edge" triggered by a FIFO threshold
When data is in the RX fifo the RX timeout interrupt goes high again even after clearing it.
The result is a deadlock because execution is stuck in the interrupt handler. No other code
can run to clear the receive buffer.
Enable and disable RX interrupts based on the buffer fill level.
Use the same approach for the TX code path.
