static int minivosc_pcm_prepare(struct snd_pcm_substream *ss)
{
// copied from aloop-kernel.c
// for one, we could get mydev from ss->private_data...
// here we try it via ss->runtime->private_data instead.
// turns out, this type of call via runtime->private_data
// ends up with mydev as null pointer causing SIGSEGV
// .. UNLESS runtime->private_data is assigned in _open?
struct snd_pcm_runtime *runtime = ss->runtime;
struct minivosc_device *mydev = runtime->private_data;
unsigned int bps;
dbg("%s", __func__);
bps = runtime->rate * runtime->channels; // params requested by user app (arecord, audacity)
bps *= snd_pcm_format_width(runtime->format);
bps /= 8;
if (bps <= 0)
return -EINVAL;
mydev->buf_pos = 0;
mydev->pcm_buffer_size = frames_to_bytes(runtime, runtime->buffer_size);
dbg2(" bps: %u; runtime->buffer_size: %lu; mydev->pcm_buffer_size: %u", bps, runtime->buffer_size, mydev->pcm_buffer_size);
if (ss->stream == SNDRV_PCM_STREAM_CAPTURE) {
/* clear capture buffer */
mydev->silent_size = mydev->pcm_buffer_size;
//memset(runtime->dma_area, 0, mydev->pcm_buffer_size);
// we're in char land here, so let's mark prepare buffer with value 45 (signature)
// this turns out to set everything permanently throughout - not just first buffer,
// even though it runs only at start?
memset(runtime->dma_area, 45, mydev->pcm_buffer_size);
}
if (!mydev->running) {
mydev->irq_pos = 0;
mydev->period_update_pending = 0;
}
mutex_lock(&mydev->cable_lock);
if (!(mydev->valid & ~(1 << ss->stream))) {
mydev->pcm_bps = bps;
mydev->pcm_period_size =
frames_to_bytes(runtime, runtime->period_size);
mydev->period_size_frac = frac_pos(mydev->pcm_period_size);
}
mydev->valid |= 1 << ss->stream;
mutex_unlock(&mydev->cable_lock);
dbg2(" pcm_period_size: %u; period_size_frac: %u", mydev->pcm_period_size, mydev->period_size_frac);
return 0;
}
/* call in cable->lock */
static void loopback_timer_start(struct loopback_pcm *dpcm)
{
unsigned long tick;
unsigned int rate_shift = get_rate_shift(dpcm);
if (rate_shift != dpcm->pcm_rate_shift) {
dpcm->pcm_rate_shift = rate_shift;
dpcm->period_size_frac = frac_pos(dpcm, dpcm->pcm_period_size);
}
if (dpcm->period_size_frac <= dpcm->irq_pos) {
dpcm->irq_pos %= dpcm->period_size_frac;
dpcm->period_update_pending = 1;
}
tick = dpcm->period_size_frac - dpcm->irq_pos;
tick = (tick + dpcm->pcm_bps - 1) / dpcm->pcm_bps;
mod_timer(&dpcm->timer, jiffies + tick);
}
