+static int aaf_mclk_start_playback(snd_pcm_aaf_t *aaf) +{
- int res;
- struct timespec now;
- struct itimerspec itspec;
- snd_pcm_ioplug_t *io = &aaf->io;
- res = clock_gettime(CLOCK_REF, &now);
- if (res < 0) {
SNDERR("Failed to get time from clock");return -errno;- }
- aaf->mclk_period = (NSEC_PER_SEC * aaf->frames_per_pkt) /
io->rate;
is this always an integer? If not, don't you have a systematic arithmetic error?
NSEC_PER_SEC is 64-bit so I don't see an arithmetic error during calculation (e.g. integer overflow). Not sure this was your concern, though. Let me know otherwise.
No, I was talking about the fractional part, e.g with 256 frames with 44.1kHz you have a period of 5804988.662131519274376 - so your math adds a truncation. same with 48khz, the fractional part is .333
I burned a number of my remaining neurons chasing a <100 ppb error which led to underruns after 10 hours, so careful now with truncation...
+static int aaf_poll_revents(snd_pcm_ioplug_t *io, struct pollfd *pfd,
unsigned int nfds, unsigned short*revents) +{
- int res;
- snd_pcm_aaf_t *aaf = io->private_data;
- if (nfds != FD_COUNT_PLAYBACK)
return -EINVAL;- if (pfd[0].revents & POLLIN) {
res = aaf_mclk_timeout_playback(aaf);if (res < 0)return res;*revents = POLLIN;- }
I couldn't figure out how you use playback events and your timer.
Every time aaf->timer_fd expires, the audio buffer is consumed by the plugin, making some room available on the buffer. So here a POLLIN event is returned so alsa-lib layer can copy more data into the audio buffer.
When there are two audio clock sources or timers that's usually where the fun begins.
Regarding scenarios with two audio clock sources or timers, the plugin doesn't support them at the moment. This is something we should work on once the basic functionality is pushed upstream.
I was talking about adjusting the relationship between your CLOCK_REALTIME timer and the media/network clock. I don't quite get how this happens, I vaguely recall there should be a daemon which tracks the difference between local and media/network clock, and I don't see it here.
Thank you for your feedback.
Regards,
Andre