On Thu, 18 Feb 2010, Lennart Poettering wrote: > On Thu, 18.02.10 10:01, Mark Brown (broonie@xxxxxxxxxxxxxxxxxxxxxxxxxxx) wrote: > >>> Now the question I have is, how should I best deal with this? I >>> currently assume that mixer volume changes are basically instantaneous >>> when I call the respective function of ALSA. But are they really? How >>> big is the latency at max? Do we need an API to query it? >> >> For the embedded case the hardware update should happen synchronously >> with the ALSA API call to adjust the setting and begin affecting the >> played audio instantaneously. The time taken to do the hardware update >> will be dominated by I/O costs, which will in turn depend on the bus >> used to access the codec - it'd be good if the buses could provide some >> information to ASoC to allow it to do an estimate, but at the minute >> we've got nothing really to go on. > > But what would you guess? In which range will this most likely be? < 1ms? > 1ms? 10ms? 100ms? 1s? 1h? 10h? 10d? 10y? Some drivers uses a queue (like HDA) for serial bus to update the audio mixer registers. But anyway, the real write should take several ms for maximum (maybe more on USB bus). > tbh I feared less the actually IO latency but more that some PCM data > fifos might need flushing before the volume is actually updated. And > the latency of those fifos I feared might be more than a handful of > samples? It's quite complex question and probably only hardware vendors knows these internals for all devices. I guess also, that some devices also uses volume ramping to avoid clicks. Jaroslav ----- Jaroslav Kysela <perex@xxxxxxxx> Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
