On Thu, 2016-03-24 at 13:24 +0100, Georg Chini wrote: > On 24.03.2016 10:36, Tanu Kaskinen wrote: > > > > On Wed, 2016-03-23 at 14:59 +0100, Georg Chini wrote: > > > > > > On 23.03.2016 14:00, Tanu Kaskinen wrote: > > > > > > > > You confirmed that pa_alsa_safe_delay() returns values that increase > > > > whenever we write more data. That indicates that the smoother is not to > > > > blame. If you substract the current ring buffer fill level from the > > > > delay value, the result should be constant. It sounds like it isn't, > > > > and that's a driver bug. > > > Not sure if I would call it a bug since the delay is reported correctly > > > by pa_alsa_safe_delay(). I think pulseaudio should be aware of such > > > behavior and be able to handle it. > > It is a bug, because of how the "delay" term is defined. If a sample is > > written to the ring buffer now, the delay tells how long it takes to > > reach the DAC. See > > http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m.html#ga012e8b999070e72ab23514f25e7d6482 > > > Yes, that is exactly what the delay reports in steady state. Only during > startup it is different. If you assume, that there is no fixed buffer on > the alsa side but that the code is just waiting for the device to start up > and is buffering data during that time, it cannot report more delay than > the amount of audio you already provided. The device might start > playing any time. So where do you see the bug? > > You are however right, if there is some fixed buffer on the alsa side, then > this should be included from the start, but I don't think there is. I will > check the alsa code to see if I can find out more. I expect there to be a fixed buffer. It doesn't make sense to me that the driver would consume data from the ring buffer when the full pipeline isn't yet running. I don't know much about what the different PCM device states really are supposed to mean, but I would expect that snd_pcm_prepare() already starts most of the sound card hardware, and snd_pcm_start() just connects the application buffer to the rest of the audio pipeline. -- Tanu
