[alsa-devel] Alsa io plugin crash question

[Hermes Zhang]

Hi all,

I am try to write a plugin in alsa io plugin mode

static snd_pcm_sframes_t
my_read (snd_pcm_ioplug_t * io,
     const snd_pcm_channel_area_t * areas,
     snd_pcm_uframes_t offset, snd_pcm_uframes_t size)
{

 }

In above function, I will copy the audio data to areas with calculate the offset like this:

memcpy((char *) areas->addr + (areas->first + areas->step * offset) / 8, data, size);

But after serveral calls, the application crash, and I print the "offset" value, it seem always increase, when reach one number (e.g. 66560) it crash. So my question is: is the "offset" value always increase is expected? Or does it should like a ring buffer, so it should start from begin again? I see there is hw_pointer and app_pointer, but they are both read_only, right? How could we adjust the read pointer? Thanks.

BTW, I test the plugin in this way:

arecord -D my_plug -c 1 -f S16_LE raw

Best Regards,
Hermes