Previously, we depended on allocated channels to always be
"dma_channel_enabled". However, (A) sometimes, many operations
would take place between find_free_audio_dma_channel and
audio_dma_enable_channel, and (B) some debugging I did led me to believe
that "dma_channel_enabled" would become false when the hardware ended
a scheduled DMA transaction, but while a CP object would still think it
owned the DMA channel.
((B) is not documented in the datasheet and I am not 100% convinced that
my debugging session was not simply missing where we were disabling the
channel, but in either case, it shows a need to directly track allocated
separately from enabled)
Therefore,
* Add audio_dma_{allocate,free}_channel.
* audio_dma_free_channel implies audio_dma_disable_channel
* track via a new array audio_dma_allocated[]
* clear all allocated flags on soft-reboot
* Convert find_free_audio_dma_channel to audio_dma_allocate_channel
* use audio_dma_allocated[] instead of dma_channel_enabled() to check
availability
* remove find_free_audio_dma_channel
* For each one, find a matching audio_dma_disable_channel to convert
to audio_dma_free_channel
Closes: #2058
.. otherwise, a sequence like
>>> a = audioio.AudioOut(board.A0)
>>> a.play(sample, loop=True)
>>> a.deinit()
would potentially leave related DMA channel(s) active.
Some ports which actually don't have audioio or audiobusio were still
calling into audio_dma_background(). This wasn't an error until
the assignment to audio_dma_state in audio_dma_stop was added, though
it's not clear why.
audio_dma_stop can be reached twice in normal usage of AudioOut.
This may bear further investigation, but stop it here, by making the
function check for a previously freed channel number. This also prevents
the event channel from being disabled twice.
The first stop location is from audio_dma_get_playing, when the buffers
are exhausted; the second is from common_hal_audioio_audioout_stop when
checking the 'playing' flag.
As identified in #1908, when both AudioOut and PDMIn are used, hard
locks can occur. Because audio_dma_stop didn't clear audio_dma_state[],
a future call to audio_dma_load_next_block could occur using a DMA
object which belongs to PDMIn.
I believe that this Closes: #1908 though perhaps it is still not the full
story.
Testing performed: Loaded a sketch similar to the one on #1908 that
tends to reproduce the bug within ~30s. Ran for >300s without hard
lock. HOWEVER, while my cpx is no longer hard locking, it occasionally
(<1 / 200s) announces
Code done running. Waiting for reload.
(and does so), even though my main loop is surrounded by a 'while True:'
condition, so there are still gremlins nearby.
