[alsa-devel] SEGFAULT : snd_pcm_mmap_begin/commit

Irfan Shaikh irfan.shaikh at sasken.com
Tue Nov 16 09:44:07 CET 2010


Hello All,

I have been facing dificulty in using snd_pcm_mmap_begin and snd_pcm_mmap_commit.
Shows Seg fault as pointed by comment in code below.
Please tell me what wrong i am doing and how do i correct.

/###################################################################################/
        unsigned int count = (alsaParams->frames/(((alsaParams->bit_per_sample)*(alsaParams->num_channel)) / 8));
        unsigned char *data = alsaParams->data;https://owa.sasken.com/owa/?ae=Item&t=IPM.Note&a=New#
        snd_pcm_sframes_t frames_available, frames_transmit;
        const snd_pcm_channel_area_t *area;
        snd_pcm_uframes_t offset;
        char *outbuffer;
        int result;

        /*available space in audio-buffer to write to*/
        frames_available = snd_pcm_avail_update(alsaParams->pcm_handle);

        /*
         * prepare the areas
         * and get back area, offset and frames_transmit
         * frames_transmit gives back the REAL value of available frames which could be written to in the mmaped-area
         * frames_transmit are less than frames_available
         */
        frames_transmit = frames_available;

        snd_pcm_mmap_begin(alsaParams->pcm_handle, &area, &offset, &frames_transmit);

        /*calculates the mmaped-buffer which could be written to*/
        outbuffer = ((char *) area->addr + (area->first + area->step * offset)/ 8);    // ****** SEGFAULT *******

        /*gives back the virtually written (writable) frames which should be always == frames_transmit*/
        result = snd_pcm_mmap_commit(alsaParams->pcm_handle, offset, frames_transmit);

        memcpy(outbuffer, data, count);  //data is actual data

I think if above code works fine should play sound.
/###################################################################################/

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