At Fri, 22 May 2009 09:07:43 +0200 (CEST), Jaroslav Kysela wrote: > > On Fri, 22 May 2009, Takashi Iwai wrote: > > > At Thu, 21 May 2009 14:44:27 -0400, > > Jon Smirl wrote: > >> > >> I've been reading Lennart's article on glitch free audio.... > >> > >> On my scatter/gather DMA hardware I generate an interrupt at the end > >> of each period. On the last period this causes ALSA to issue a > >> trigger(STOP). However, there is a latency from when that interrupt is > >> generated and when ALSA does the trigger(STOP). During that latency my > >> hardware starts playing the next buffer (which contains stale data). > >> Playing stale data causes a noise burst. I fixed this by programming > >> my DMA hardware to not overrun appl_ptr. > >> > >> There's another solution. ALSA already knows the stream ends > >> mid-period and pads out the partial period with silence. If it simply > >> padded out the next period with silence too the overrun problem would > >> become non-audible and there would time to process trigger(STOP). > >> > >> If padding out two periods at end of stream is possible, it then > >> becomes possible for me to turn off interrupts in my audio driver. > > > > This can be another interesting feature. For example, you could add > > a soft-mute padding to avoid a click noise at the end instead of a > > whole silence. > > > > But, this kind of hack really depends on the hardware implementation. > > If a hardware has no DMA but require explicit writes, adding two > > periods is too much. Just a few samples would be enough. > > I agree to leave such things to lowlevel drivers. > > > Or, in the case of normal PCI DMA transfer, how can it be stopped? > > That is, the stream is still running although it's claimed to be > > stopped. If a period size is big (say over one second), the stop at > > the next interrupt doesn't sound good. > > I would suggest to improve drain() logic in kernel with > snd_pcm_update_hw_ptr() calls and using proper timeouts for > schedule_timeout(). > > Note that this situation were handled with dead and removed pcm tick API - > although it required assistance (setup) from application. ... and, the results was no one used it :) Apps don't want to set up such details at all -- that's the lesson we had to learn... Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
