periods*period_size vs. buffer_size; should they be equal?
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I'm attempting to understand the layout of the DMA buffer used by ASoC devices. It seems like the buffer should consist of runtime->periods entries each of runtime->period_size frames of audio data. Hence, runtime->buffer_size should be equal to runtime->periods * runtime->period_size in frames. This assumption holds true in many cases. However, it doesn't in others: (sizes in hex) Playing WAVE '8000.wav' : Signed 16 bit Little Endian, Rate 8000 Hz, Stereo [ 217.910867] Trigger: runtime->periods=4 [ 217.914696] Trigger: runtime->period_size=3e8 [ 217.919043] Trigger: runtime->buffer_size=fa0 [ 217.923389] Trigger: f2b(4)=10 Playing WAVE '11025.wav' : Signed 16 bit Little Endian, Rate 11025 Hz, Stereo [ 268.543821] Trigger: runtime->periods=5 [ 268.547651] Trigger: runtime->period_size=400 [ 268.551998] Trigger: runtime->buffer_size=1589 Playing WAVE '16000.wav' : Signed 16 bit Little Endian, Rate 16000 Hz, Stereo [ 315.889280] Trigger: runtime->periods=7 [ 315.893109] Trigger: runtime->period_size=400 [ 315.897456] Trigger: runtime->buffer_size=1f40 Yet for any higher sample rate the layout is identical: Playing WAVE '96000.wav' : Signed 16 bit Little Endian, Rate 96000 Hz, Stereo [ 385.494764] Trigger: runtime->periods=8 [ 385.498594] Trigger: runtime->period_size=400 [ 385.502941] Trigger: runtime->buffer_size=2000 Is my assumption wrong? Is there some bug somewhere? The reason I ask is because the DMA engine I'm writing for doesn't directly handle circular buffers. Hence, I'm kicking off a separate DMA request for each period's worth of data. Originally, the code was wrapping based on runtime->buffer_size, but this didn't work correctly when buffer_size wasn't a multiple of the period size. Thanks for any pointers! -- nvpublic _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel