Add RP2 PIO background read

[timchinowsky]

This PR adds a background_read method to rp2pio.StateMachine to complement the existing background_write.

[jepler]

Thanks for this, I'm excited!

I did have some review comments & requested changes. I also didn't actually test the code. Any suggestion on something that would be useful to try/test if I don't have a TAC5xxx codec?

[timchinowsky]

Thanks for this, I'm excited!

I did have some review comments & requested changes. I also didn't actually test the code. Any suggestion on something that would be useful to try/test if I don't have a TAC5xxx codec?

For testing with no codec, I'm getting together a loopback example similar to https://github.com/adafruit/Adafruit_CircuitPython_PIOASM/blob/main/examples/pioasm_i2s_codec.py that will send a background_write to a background_read by connecting output and input data pins. If you're interested in messing with the codec itself, I've got some extras I could send you, let me know.

[timchinowsky]

Any suggestion on something that would be useful to try/test if I don't have a TAC5xxx codec?

I've added a loopback example at https://github.com/timchinowsky/tac5 which you should be able to run as is on a Feather RP2040 if you connect DOUT (D9) to DIN (D10).

[timchinowsky]

The last two commits add double buffering and a last_read property which (a) returns the buffer which was last completely filled by background reads and (b) self-clears, so that if the property is read again before the next buffer swap, it will return an empty buffer. This allows data read in the background to be recorded to SD with code as simple as

with open(filename, 'w') as f:
    while True:
        f.write(self.pcm.pio.last_read)

With the double-buffering and last_read property there are a lot of sm_buf_info's and mp_obj_t buffer objects hanging around, which I'm hoping to improve, but it seems to work. In the saved file I can see

The four-line sections starting with F7 and F6 are written from alternating buffers, and have the expected content.

[timchinowsky]

Background playback of 8-channel audio from SD card to a 4-codec TAC5212 setup now working! Details at https://github.com/timchinowsky/tac5.

[relic-se]

Hey @timchinowsky ! I've been loving this new feature and have recently implemented in a simple general purpose I2S library: https://github.com/relic-se/CircuitPython_I2SInOut. So far so good, but if you need any assistance with reviewing these updates further, let me know how I can help.

[timchinowsky]

@relic-se that's great, thanks for letting me know!

[relic-se]

I'm not certain exactly what your goals in the recent updates are, but rather than building bespoke audio DSP processes for the rp2pio module, it would likely be better to find a way to integrate it into the existing audio systems of CircuitPython using the audiosample API. That way the existing processing modules could be used with custom PIO systems (ie: audiomixer, audiofilters, audiodelays, + future additions).

Alternatively, a separate audiobusio.I2Sin class could be created with the sole purpose of being an audio source in these existing modules (see audiocore.RawSample as an example). I've been working on this particular addition on the side, but it's not yet ready to share.

[relic-se]

It's also possible to feed data from rp2pio into an audiocore.RawSample buffer when double-buffering is enabled using the background_read functionality. See the "effect" example in the library I shared earlier for a demonstration of this: https://github.com/relic-se/CircuitPython_I2SInOut/blob/master/examples/i2sinout_effect.py.

[timchinowsky]

I'm not certain exactly what your goals in the recent updates are, but rather than building bespoke audio DSP processes for the rp2pio module, it would likely be better to find a way to integrate it into the existing audio systems of CircuitPython using the audiosample API.

Yes, totally. I was thinking when I started this that I would be leaning more on audiocore, but its limitations (<=16-bit, <=2 channels) made it difficult to explore the full capabilities of the codec I am working with. Now that I've got the codec working well with rp2pio I'm going to see what can be done as far as unification. For example, suppose that an 8-channel ADC could present as 8 mono rawsample-like objects or 4 stereo objects, etc., and that an 8-channel DAC could present as 4 stereo I2SOut objects, and so forth.

That said, I also like the idea of enabling ulab-like procedural processing of signals, to complement synthio's declarative style. I first got into CircuitPython as a tool for teaching electrical engineering lab classes, and making the signal processing more explicit and transparent would be great for that application.

I'm also planning to continue filling out the API for the TAC5212 codec. For instance, the part has built in biquad filters on both ADCs and DACs (up to 3 per channel) and optional loopback between ADC and DAC, so the part can be used to implement 6-stage biquad analog-in/analog out filtering without any microcontroller involvement at all.

[relic-se]

Yes, totally. I was thinking when I started this that I would be leaning more on audiocore, but its limitations (<=16-bit, <=2 channels) made it difficult to explore the full capabilities of the codec I am working with. Now that I've got the codec working well with rp2pio I'm going to see what can be done as far as unification. For example, suppose that an 8-channel ADC could present as 8 mono rawsample-like objects or 4 stereo objects, etc., and that an 8-channel DAC could present as 4 stereo I2SOut objects, and so forth.

Okay, I see where you're coming from here. Multi-channel output is fairly niche, so I don't think it's at the forefront of development in those areas. Yet, I don't see why one could operate with multiple mono/stereo outputs simultaneously as you've described for the time being.

As I've been playing around more with the API, I do think it's possible to connect an object like audiocore.RawSample to a StateMachine input and audioio.AudioOut as an output. For multi-channels, a few parameters like channel_spacing (total number of channels), channel_offset (starting channel index), and channel_count (mono/stereo) could be used to iterate through the appropriate buffers.

That said, I also like the idea of enabling ulab-like procedural processing of signals, to complement synthio's declarative style. I first got into CircuitPython as a tool for teaching electrical engineering lab classes, and making the signal processing more explicit and transparent would be great for that application.

Currently, the new process method feels out of scope for rp2pio. I think it would make much more sense to provide a separate DSP library that acts like ulab that you could operate directly on WriteableBuffer objects as you've described.

I'd really like to see the new background_read additions be added to the core. I think it might be best to save these new additions for another PR rather combine them with this one.

[timchinowsky]

SGTM 🚀

[timchinowsky]

Not sure why the espressif builds are failing, any suggestions @relic-se @jepler? Thanks! Perhaps related, my submodule understanding is fuzzy, do I need to do something get rid of the git warnings

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   ports/espressif/esp-idf (new commits)
	modified:   ports/raspberrypi/sdk (new commits)

[dhalbert]

There are three regressions in submodule versions. See the first three entries in "Files changed". There shouldn't be any submodules listed in there for this PR> You can update submodules locally and then push again. The submodules don't get updated automatically necessarily when you merge from upstream.

[timchinowsky]

There are three regressions in submodule versions. See the first three entries in "Files changed". There shouldn't be any submodules listed in there for this PR> You can update submodules locally and then push again. The submodules don't get updated automatically necessarily when you merge from upstream.

Thanks @dhalbert! I can update locally with make fetch-all-submodules but then how do I push the submodules? The various advice I am seeing on stackoverflow is not giving me a warm feeling.

[dhalbert]

I can update locally with make fetch-all-submodules but then how do I push the submodules?

You commit the changed commits for the submodules.