WIP: Implement 'ParallelImageCapture' for samd51

[jepler]

This work-in-progress code, together with a WIP CircuitPython library, can successfully capture small (80x60) frames from an OV7670 camera on a Metro M4 GrandCentral.

TODO:

• a name everyone can agree on
• capture using DMA, rather than having interrupts disabled for 30ms

[tannewt]

Thanks for the module rename. I like imagecapture. Just a couple other minor things.

I think you need per-param comments for the constructor too.

[jepler]

@tannewt this is ready for a fresh review.

Main question I have right now is, I used "audio_dma" channels. As far as I can see this will work just fine (but didn't test): with 3 channels you can play stereo audio in the background and capture a framebuffer image in the foreground; we'd have to increase the channel count in the future when we enable this or audio capture to also happen in the background. That said, should the APIs audio_dma_allocate_channel() and audio_dma_free_channel be renamed? Be moved to different locations? Or can it be left as-is?

[tannewt]

I think it would be good to rename the audio_dma stuff. I'm trying to remember what makes those special so we could rename them that way. Is it that they can be triggered by events?

[jepler]

@tannewt this is ready for a fresh review assuming the CI passes. Let me know if I need to merge main or rebase onto it.

[tannewt]

Code looks good. Thank you! You'll need to fix the CI though.

[tannewt]

Thank you!

[jepler]

@ladyada
Test program for ov7670 + gcm4 + 1.8" tft shield: https://gist.github.com/645f7d052b63103111b011e507df38a1
Test program for ov7670 + rpi pico + 2.0" ST7789 breakout: https://gist.github.com/f357464e194a4ba85bbcd43378b1e189

I think the 2nd one needs the fix for the DIV2 resolution mode, adafruit/Adafruit_CircuitPython_OV7670#4