From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christophe Aeschlimann Subject: davinci-pcm.c : snd_pcm_hardware.periods_min value Date: Thu, 5 Jul 2012 10:52:14 +0200 Message-ID: <4FF555BE.7090509@acn-group.ch> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: Errors-To: davinci-linux-open-source-bounces-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org To: Davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org Cc: "alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org" , vbarinov-hkdhdckH98+B+jHODAdFcQ@public.gmane.org List-Id: alsa-devel@alsa-project.org Hi, We are working with an OMAP-L138 attached to a TI stereo codec (TLV320AIC3107) using McASP and we are trying to reduce the latency on the playback path. We are using the real-time patches on a 3.0.y longterm stable kernel. In /sound/soc/davinci/davinci-pcm.c I can see the following structure: > static struct snd_pcm_hardware pcm_hardware_playback =3D { > .info =3D (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER | > SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID | > SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME), > .formats =3D (SNDRV_PCM_FMTBIT_S16_LE), > .rates =3D (SNDRV_PCM_RATE_8000 | SNDRV_PCM_RATE_16000 | > SNDRV_PCM_RATE_22050 | SNDRV_PCM_RATE_32000 | > SNDRV_PCM_RATE_44100 | SNDRV_PCM_RATE_48000 | > SNDRV_PCM_RATE_88200 | SNDRV_PCM_RATE_96000 | > SNDRV_PCM_RATE_KNOT), > .rate_min =3D 8000, > .rate_max =3D 96000, > .channels_min =3D 2, > .channels_max =3D 2, > .buffer_bytes_max =3D 128 * 1024, > .period_bytes_min =3D 32, > .period_bytes_max =3D 8 * 1024, > .periods_min =3D 16, > .periods_max =3D 255, > .fifo_size =3D 0, > }; Which I think affects the minimum latency achievable. I would like to know if there is a reason why the periods_min is set to such a high value (16) ? (comparatively to most drivers). I'd welcome any information :) Best regards, -- = Christophe Aeschlimann Embedded Software Engineer & IT Manager ACN Advanced Communications Networks S.A. 2000 - Neuch=E2tel, Switzerland Tel. +41 32 724 74 31