[alsa-devel] what is period_size, buffer_size and boundary size, i confuse them

l9jj at 163.com l9jj at 163.com
Mon Dec 10 09:09:04 CET 2012

thank you very much.
(1)what is the relationship between DMA buffer size and the boundary
size?does  the variable buffer_size equal to  DMA size?
(2)how the pos>buffer_size will happen in the interface snd_pcm_update_hw_ptr0()? the variable pos is in the range of DMA_size,it can not bigger than the buffer_size.it blocked me.

thanks a lot.

在 2012-12-10 00:23:55, Clemens Ladisch <clemens at ladisch.de>写道:
l9jj wrote:
> can anyone help me to figure out  the concepts between period_size ,buffer_size and boundary size?
> n * period_size = buffer_size?

Yes.  On many devices, n is not required to be an integer.

> m * buffer_size = boundary_size?

Yes, where m is very big.  In applications, the actual value of the boundary
size does not matter (except as a special value for some sw params).

> and how the dma buffer mapped to the alsa buffer?

The DMA buffer _is_ the ALSA buffer.

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