[alsa-devel] Direct write (using mmap_bigin and commit)

Irfan Shaikh irfan.shaikh at sasken.com
Mon Nov 15 13:24:20 CET 2010


         I am reading an raw PCM  file and want to write on PCM device using direct write (interleaved). I have gone through PCM.c test application.
I am trying tio write PCM audio data as follows. I am unable to use  snd_pcm_mmap_begin and snd_pcm_mmap_commit properly. Please help me to use using these APIs
Question :
1) How can i write to Ring buffer area (any pcm audio data)?  //Any example or explanation other than pcm.c
2) Do i need to write diffferently for each channel as shown in pcm.c

I am trying to do following but not succeded (reading pcm file and writing content on device) . ANy thing played on audio device would help me in understanding.

        snd_pcm_channel_area_t my_areas;
        snd_pcm_uframes_t offset, frames, size;
        snd_pcm_sframes_t avail, commitres;
        int result;
        char *buffer;

            avail = snd_pcm_avail_update(handle);
                while (size > 0) {
                        frames = size;
                        err = snd_pcm_mmap_begin(handle, &my_areas, &offset, &frames);
                        mybuffer=(char *)malloc(frames*2);
                        result = fread (mybuffer,1,(frames*2),pFile);
                        my_areas.addr=mybuffer;           // IS THIS CORRECT ? WILL THIS WORK ? How can i write my audio file data here in areas?
                        commitres = snd_pcm_mmap_commit(handle, offset, frames);

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