Re: [alsa-devel] ALSA buffer query

Thanks for reply,

Please tell me if my understanding is correct

1) Check number of frames ready to be written in DMA area - using snd_pcm_avail_update 2) Call snd_pcm_mmap_begin(snd_pcm_t * pcm, const snd_pcm_channel_area_t ** areas, snd_pcm_uframes_t * offset, snd_pcm_uframes_t * frames)

(what does offfset specify here ?)

3) I need to fill my audio data to be played in area {Please tell me if this is correct}

4) snd_pcm_mmap_commit(pcm_handle, offset, frames);

Please tell me is my understanding correct to play my audio buffer on ASLA playback device.

I am not clear about where do i write my audio payload ? And how offset in snd_pcm_mmap_begin is realted to it ?

Thanks and Regards,

________________________________________ From: Jaroslav Kysela [perex@perex.cz] Sent: Thursday, November 11, 2010 12:48 PM To: Irfan Shaikh Cc: alsa-devel@alsa-project.org Subject: Re: [alsa-devel] ALSA buffer query

On Thu, 11 Nov 2010, Irfan Shaikh wrote:

Hello All,

 1) My understanding :  snd_pcm_writei() takes the allocated buffer

from applications and passes the buffer beneath to the ASLA library and then to the ALSA driver for rendering Audio.

 2) Query 1 : Instead of me allocating the buffer in ALSA

application and passing the pointer in snd_pcm_writei, Can ALSA allocate the buffer and give to my application, so that i can copy my data into it.

 3) Query 2 : Is there any wayto diirectly get hardware ALSA buffer

from the ALSA driver to application so that i can copy PCM data to this buffer directly. If not, is there any way can we do this ?

Read alsa-lib documentation. snd_pcm_mmap_begin/snd_pcm_mmap_commit.

Jaroslav

----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.

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