It was intended to allow changing baudrate on shared spi/i2c. There's no
advantage in using it for PWM or PIO, and makes it less usable because you have to
have `embassy-embedded-hal` as a dep to use it.
the many individual sets aren't very efficient, and almost no checks
were done to ensure that the configuration written to the hardware was
actually valid. this adresses both of these.
programs contain information we could pull from them directly and use to
validate other configuration of the state machine instead of asking the
user to pull them out and hand them to us bit by bit. unfortunately
programs do not specify how many in or out bits they use, so we can only
handle side-set and wrapping jumps like this. it's still something though.
this *finally* allows sound implementions of bidirectional transfers
without blocking. the futures previously allowed only a single direction
to be active at any given time, and the dma transfers didn't take a
mutable reference and were thus unsound.
move all methods into PioStateMachine instead. the huge trait wasn't
object-safe and thus didn't have any benefits whatsoever except for
making it *slightly* easier to write bounds for passing around state
machines. that would be much better solved with generics-less instances.
not requiring a PioInstance for splitting lets us split from a
PeripheralRef or borrowed PIO as well, mirroring every other peripheral
in embassy_rp. pio pins still have to be constructed from owned pin
instances for now.
merge into PioInstance instead. PioPeripheral was mostly a wrapper
around PioInstance anyway, and the way the wrapping was done required
PioInstanceBase<N> types where PIO{N} could've been used instead.
instruction memory is a shared resource. writing it only from PioCommon
clarifies this, and perhaps makes it more obvious that multiple state
machines can share the same instructions.
this also allows *freeing* of instruction memory to reprogram the
system, although this interface is not entirely safe yet. it's safe in
the sense rusts understands things, but state machines may misbehave if
their instruction memory is freed and rewritten while they are running.
fixing this is out of scope for now since it requires some larger
changes to how state machines are handled. the interface provided
currently is already unsafe in that it lets people execute instruction
memory that has never been written, so this isn't much of a drawback for now.
