samd: When possible, use one DMA channel for stereo AudioOut #2552
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.. the documentation doesn't make this clear, but in practice it works to write both of the DATABUF registers at the same time. This should also reduce the amount of wear and tear DMA puts on the system, as the number of transfers is cut in half. (the number of bytes transferred remains the same, though) In principle, this could cover all stereo cases if audio_dma_convert_signed also learned to 16-bit extend and swap values. However, this is the case that matters for stereo mp3 playback on PyGamer. Testing performed: Listened to some tracks with good stereo separation.
With the previous change, stereo mp3 playback changed from needing 4 2304-byte allocations to needing 2 4604-byte allocations. This was enough to cause MemoryErrors with regularity. By using m_realloc() here, the existing memory region can be used. m_realloc() also works on the first invocation, because m_realloc(NULL, sz) just calls m_malloc of sz.
tannewt
approved these changes
Jan 27, 2020
6 tasks
This was referenced May 15, 2020
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.. the documentation doesn't make this clear, but in practice it works to write both of the DATABUF registers at the same time. This should also reduce the amount of wear and tear DMA puts on the system, as the number of transfers is cut in half. (the number of bytes transferred remains the same, though)
In principle, this could cover all stereo cases if audio_dma_convert_signed also learned to 16-bit extend and swap values. However, this is the case that matters for stereo mp3 playback on PyGamer.
Testing performed: Listened to some tracks with good stereo separation.
This will end up conflicting with #2533, which should be rebased if this is accepted first. In fact, if this is accepted, then in lieu of #2533 it is probably better to extend audio_dma_convert_signed and ditch the sibling dma channel code. Other parts of that PR would still apply, as far as getting rid of the "single channel" flags through the audio stack.