[alsa-devel] snd_pcm_hardware structure

Adish Kuvelker adkuvi at gmail.com
Wed Jun 23 19:57:36 CEST 2010

Hello James,
Thanks a lot....Just a typo error for the period_bytes_min and
period_bytes_max in my mail.....

Now that my FIFO is 64 bytes and if I need an interrupt to the CPU for
FIFO being half-empty (i.e 32 bytes = 16 16-bit samples), would it be
right to set the periods_min = periods_max = 32?


On Wed, Jun 23, 2010 at 11:15 PM, James Courtier-Dutton
<james.dutton at gmail.com> wrote:
> On 23 June 2010 18:22, Adish Kuvelker <adkuvi at gmail.com> wrote:
>> Hello,
>> I am developing a ALSA driver for the AtlasIII AC'97 Controller. The
>> AC'97 Controller FIFO is arranged as 16 32-bit entries. My PCM data
>> would be 16-bit samples and the driver will cater to 2-front channel
>> audio. I have configured the snd_pcm_hardware members as follows:
>> .formats = SNDDRV_PCM_FMTBIT_S16_LE
>> .period_bytes_max = 4,
>> .period_bytes_min = 64,
>> As I would need a minimum of 4-byte sample to be transferred and the
>> "period_bytes_max" value has been set considering the maximum size of
>> the FIFO in bytes. Is my understanding correct in doing these
>> settings?
>> Secondly, I am having slight problems in understanding the
>> "snd_pcm_hardware" members periods_min and periods_max. Can anyone
>> throw some more light on this in addition to what is explained in the
>> "Writing an Audio Driver"?
> max should = 64
> min should = 4
> periods_min and periods_max is dependent on when the sound card
> interrupts the CPU.
> So, if the CPU gets an interrupt once every 16 samples, then
> periods_min = periods_max = 1
> If the sound card does not interrupt the CPU at all, you have to
> provide a method to notify the CPU when to next fill the FIFO.

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