execution wraps around after the end of instruction memory and wrapping
works with this, so we may as well allow program loading across this
boundary. could be useful for reusing chunks of instruction memory.
sometimes state machines need to be started, restarted, or synchronized
at exactly the same time. the current interface does not allow this but
the hardware does, so let's expose that.
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.
none of these are safe. the x/y functions mangle the fifos, the set
functions require the state machine to be stopped to be in any way safe,
the out functions do both of those things at once. only the jump
instruction is marginally safe, but running this on an active program is
bound to cause problems.
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.
there's nothing this critical section protects against. both read and
write-to-clear are atomic and don't interfere with other irq futures,
only potentially with setting/clearing an irq flag from an arm core.
neither have ever been synchronized, and both have the same observable
effects under atomic writes and critical sections. (for both setting and
clearing an irq flag observable differences could only happen if the
set/clear happened after the poll read, but before the write. if it's a
clear we observe the same effects as sequencing the clear entirely after
the poll, and if it's a set we observe the same effects as sequencing
the set entirely before the poll)
it's only any good for PioPin because there it follows a pattern of gpio
pin alternate functions being named like that, everything else can just
as well be referred to as `pio::Thing`
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.
this way we can share irq handling between state machines and common
without having to duplicate the methods. it also lets us give irq flag
access to places without having to dedicate a state machine or the
common instance to those places, which can be very useful to eg trigger
an event and wait for a confirmation using an irq wait object.
we can only have one active waiter for any given irq at any given time.
allowing waits for irqs on state machines bypasses this limitation and
causes lost events for all but the latest waiter for a given irq.
splitting this out also allows us to signal from state machines to other
parts of the application without monopolizing state machine access for
the irq wait, as would be necessary to make irq waiting sound.
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.
once all sharing owners of pio pins have been dropped we should reset
the pin for use by other hal objects. unfortunately this needs an atomic
state per pio block because PioCommon and all of the state machines
really do share ownership of any wrapped pins. only PioCommon can create
them, but all state machines can keep them alive. since state machines
can be moved to core1 we can't do reference counting in relaxed mode,
but we *can* do relaxed pin accounting (since only common and the final
drop can modify this).
we can't prove that some instruction memory is not used as long as state
machines are alive, and we can pass instance memory handles between
instances as well. mark free_instr unsafe, with documentation for this caveat.
1425: rp pio, round 2 r=Dirbaio a=pennae
another round of bugfixes for pio, and some refactoring. in the end we'd like to make pio look like all the other modules and not expose traits that provide all the methods of a type, but put them onto the type itself. traits only make much sense, even if we added an AnyPio and merged the types for the member state machines (at the cost of at least a u8 per member of Pio).
Co-authored-by: pennae <github@quasiparticle.net>
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.
1423: rp: fix gpio InputFuture and inefficiencies r=pennae a=pennae
InputFuture could not wait for edges without breaking due to a broken From impl, but even if the impl had been correct it would not have worked correctly because raw edge interrupts are sticky and must be cleared from software. also replace critical sections with atomic accesses, and do nvic setup only once.
Co-authored-by: pennae <github@quasiparticle.net>
doing this setup work repeatedly, on every wait, is unnecessary. with
nothing ever disabling the interrupt it is sufficient to enable it once
during device init and never touch it again.
pio control registers are notionally shared between state machines as
well. state machine operations that change these registers must use
atomic accesses (or critical sections, which would be overkill).
notably PioPin::set_input_sync_bypass was even wrong, enabling the
bypass on a pin requires the corresponding bit to be set (not cleared).
the PioCommon function got it right.
fixing the dma word size to 32 makes it impossible to implement any
peripheral that takes its data in smaller chunks, eg uart, spi, i2c,
ws2812, the list goes on.
compiler barriers were also not set correctly; we need a SeqCst barrier
before starting a transfer as well to avoid reordering of accesses into
a buffer after dma has started.
InputFuture did not use and check edge interrupts correctly.
InterruptTrigger should've checked for not 1,2,3,4 but 1,2,4,8 since the
inte fields are bitmasks, and not clearing INTR would have repeatedly
triggered edge interrupts early.
1414: rp: report errors from buffered and dma uart receives r=Dirbaio a=pennae
neither of these reported errors so far, which is not ideal. add error reporting to both of them that matches the blocking error reporting as closely as is feasible, even allowing partial receives from buffered uarts before errors are reported where they would have been by the blocking code. dma transfers don't do this, if an errors applies to any byte in a transfer the entire transfer is nuked (though we probably could report how many bytes have been transferred).
Co-authored-by: pennae <github@quasiparticle.net>
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.
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.
