The "spacing" of "buffer structure" is confusing, use the "channel count"
instead.
Testing performed on nrf52840 feather:
Play stereo and mono, 8- and 16-bit, 8kHz RawSamples representing 333.33Hz
square waves.
Use both mono and stereo PWMAudioOut instances.
Scope the RC-filtered signal and use the scope's frequency
measurement function, verify the frequency is 333 or 334Hz in all tested
cases.
In the "stereo output" cases, verify both the L and R channels. Verify
the output amplitude is the same in both channels.
In the "stereo output" cases, run a second test where the L channel's
amplitude is attenuated 50%. Verify the output amplitude is correct
in each channel.
.. otherwise, when an AudioPWMOut object was deinitted without being
explicitly stop()ped, it would use up a slot in active_audio[]; the
5th iteration would create a non-working audio object which would just
buzz instead of playing the right thing.
Closes: #2203
The original formulation was because I saw the need to avoid a transition
from playing to stopped exactly when a resume was taking place. However,
@tannewt was concerned about this pause causing trouble, because it could
be relatively lengthy (several ms even in a typical case).
After reflection, I've convinced myself that updating the registers
in this order in resume avoids a window where a "stopped" event can
be missed as long as the shortcut is updated first.
Testing re-performed: pause/resume testing of looped RawSample and
WaveFile audio sources.
