At Mon, 11 May 2009 11:50:22 -0400, Jon Smirl wrote: > > On Mon, May 11, 2009 at 11:40 AM, Takashi Iwai <tiwai@xxxxxxx> wrote: > > At Mon, 11 May 2009 11:11:55 -0400, > > Jon Smirl wrote: > >> > >> On Mon, May 11, 2009 at 9:45 AM, Jaroslav Kysela <perex@xxxxxxxx> wrote: > >> > On Mon, 11 May 2009, Jon Smirl wrote: > >> > > >> >>> Right. This is the value to check in your case. > >> >> > >> >> What do think about redesigning the ALSA DMA interface to support > >> >> detection of over and under run? Leaving the DMA engine in a loop and > >> >> not coordinating with ALSA as to where the valid data is does not seem > >> >> to be a safe way of exchanging data. That interface may be a source of > >> >> the problems pulseaudio is encountering. > >> >> > >> >> A simple solution would be for snd_pcm_period_elapsed() to return > >> >> physical address of the last valid sample. That would let me avoid > >> >> playing with s->runtime->control->appl_ptr. You could provide the > >> >> same data in the pointer() function. > >> > > >> > More simpler solution is to check the stream state in the low level driver. > >> > If it's in DRAINING state, then end of stream is signaled from the > >> > application and driver might not queue next buffer. We may also add another > >> > callback (or use ioctl callback) to pass this stream state change to the > >> > lowlevel driver immediately, so the driver might react more quickly on this > >> > situation. > >> > > >> > >> Quickness is the wrong way to think about this problem. ALSA knows exactly > >> when it has placed valid data into the buffer. > > > > Not really. When the mmap mode is used, the update isn't always > > notified to the driver and the transfer can be completely > > asynchronous. > > This seems to me to be a broken design. ALSA is being put into the > position of guessing when the application has supplied new data. > Shouldn't the app be required to make a commit() call after filling in > the data? Without commit it is impossible to detect over/underrun. The commit updates the mmapped control data (so that it works even without the context switch) if the architecture supports. In other cases, a commit issues an explicit sync ioctl. Actually it should be possible to disable the mmap-control mode explicitly, but right now it's not done from the driver side but only checks the architecture. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
