linguini1 opened a new pull request, #19406:
URL: https://github.com/apache/nuttx/pull/19406
## Summary
This PR introduces support for PWM-based audio on the Raspberry Pi 4B:
- PWM driver support for both channels of PWM0 and PWM1 (audio jack PWM)
- Oneshot timer support for the (4) BCM2711 system timers
- Device driver registration for PWM and audio tone drivers
- A configuration with the PWM example to test audio, which is documented
The PWM audio isn't the best sounding because it is PWM. There have been
suggestions on how to improve NuttX's audio support to allow translating PCM
audio to PWM with DMA, but for now that is beyond the scope of these
improvements.
## Impact
Closes #16950.
Closes #19374.
Part of my GSoC milestones, completing the audio jack support milestone.
Really hurts your ears if you wear earbuds to test; I recommend a device
with its own analog volume control knob, and cautiously testing the volume of
the sound before committing to wearing earbuds/headphones. I put this warning
in the docs, but this is a warning to reviewers too!
## Testing
Built the PWM audio configuration that is included in this PR and verified
on the device that audio comes through the headphone jack. To my (not perfectly
trained ears), the audio frequencies I set for a few notes (i.e. middle C) have
sound which matches what my desktop computer played for a recording of middle C
I found online.
I also registered the one-shot driver as a character driver and performed
the one-shot test, which passed:
```console
nsh> oneshot
oneshot_ioctl: cmd=5664 arg=004de0a0
oneshot_ioctl: cmd=5665 arg=004de0b0
bcm2711_tim_irq_en: Interrupt for timer 0 enabled.
Opening /dev/oneshot0
Maximum delay is 18446744073709551615
Starting oneshot timer with delay 2000000 microseconds
Waiting...
bcm2711_tim_irq_en: Interrupt for timer 0 disabled.
bcm2711_tim_handler: Callback...
bcm2711_tim_handler: Callback called for oneshot 0.
Finished
```
And finally, I checked the PWM0 interface output using my logic analyzer and
both the frequency and duty cycle settings seem to work perfectly fine:
<img width="1815" height="648" alt="swappy-20260708_201755"
src="https://github.com/user-attachments/assets/67266a60-eb5c-464f-879e-66a59aec2a9b";
/>
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