At Sun, 24 May 2009 19:26:42 -0700, Troy Kisky wrote:
Does
(substream->dma_buffer.bytes) need to equal (snd_pcm_lib_period_bytes(substream) * runtime->periods) ?
When this is not true, it seems like the buffer is not being filled correctly.
for testing, this works .buffer_bytes_max = 16 * 7 * 512, .period_bytes_min = 32, .period_bytes_max = 7 * 512, /* This is size of ping + pong buffer*/
and this doesn't. .buffer_bytes_max = 16 * 7 * 512 + 512, .period_bytes_min = 32, .period_bytes_max = 7 * 512, /* This is size of ping + pong buffer*/
When playing back a sine wave, I can hear breaks.
Well, there are two misunderstandings here:
- substream->dma_buffer.bytes doesn't define the actual buffer size. It's substream->runtime->buffer_size (in frames). The former is the allocated buffer size which can be larger.
- The buffer size doesn't have to be aligned to period_size as default, i.e. it's not always equal with period_size * periods, and periods isn't always an integer.
To align the buffer size to period size, call below in the open callback snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
HTH,
Takashi