drivers/periph/dac: add dac_play API for async multi sample output - #22261
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drivers/periph/dac: add dac_play API for async multi sample output#22261benpicco wants to merge 6 commits into
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The `dac_set()` API says > The value is always given as 16-bit value and is internally scaled to the > actual resolution that the DAC unit provides (e.g. 12-bit). We didn't do that scaling before - enable it even though it breaks existing users.
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I think they are already fixed in this branch 🤔 |
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Contribution description
The
periph_dacAPI only plays single samples. Thedac_ddsdrives does exist, but it's interrupt based so it's prone to distortions when interrupts are disabled even for a brief time.The proper solution is to use DMA to feed the DAC and since the DAC API is CPU specific, the only way to do this is by extending the DAC API with a new
dac_play()function that allows to supply a buffer of samples that will then be played asynchronously.Support for this is indicated by the
periph_dac_playfeature.We can supply a completion callback to supply the next buffer or set it to loop mode where the same sample is played over and over again independent of the CPU (e.g. if we want to produce a constant sine wave).
dac_set()behaves on sam0Previously the 12 bit DAC was not left-adjusted, that means
dac_set(0xfff)would produce the highest amplitude whiledac_set(0x1000)would be clipped to 0.However our API doc says
Fix this by setting the
LEFTADJbit.This however means that existing users will experience a lower amplitude when they supply 12 bit values.
Testing procedure
Try out the different waveforms in
tests/periph/dac_play:(The overshooting for square and sawtooth waves are actually an artifact of the oscilloscope, the signal looks clean on the (more expensive) Tektronix scope)
Issues/PRs references
Declaration of AI-Tools / LLMs usage:
AI-Tools / LLMs that were used are: