As the main author of the Aureal Vortex driver, its very stupid having
to handle arbitrary period sizes, introducing a lot of overhead and
complexity in the driver, while the hardware just is not designed to
handle period sizes that are not powers of two, due to page boundary
overlapping trouble.
You don't have to handle arbitary period sizes in the alsa-driver.
Here is an example from the emu10k1 driver, that restricts what period sizes the application can use for caputure.
static unsigned int capture_period_sizes[31] = {
384, 448, 512, 640,
384*2, 448*2, 512*2, 640*2,
384*4, 448*4, 512*4, 640*4,
384*8, 448*8, 512*8, 640*8,
384*16, 448*16, 512*16, 640*16,
384*32, 448*32, 512*32, 640*32,
384*64, 448*64, 512*64, 640*64,
384*128,448*128,512*128
};static snd_pcm_hw_constraint_list_t hw_constraints_capture_period_sizes = {
.count = 31,
.list = capture_period_sizes,
.mask = 0
};static int snd_emu10k1_capture_open(snd_pcm_substream_t * substream)
{
<snip>
snd_pcm_hw_constraint_list(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, &hw_constraints_capture_period_sizes);
<snip>
Has a driver writer, you have full control over these sorts of things.
Cheers James
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