Kai Vehmanen wrote: > > On Thu, 14 Feb 2002, Jaroslav Kysela wrote: > > >> - ALSA is unable to detect xruns inside mmap_begin()->mmap_commit() > >> code block > > I wonder why you say this. There is really very short time period in which > > the hardware pointer can cross the application pointer and PCM code won't > > react on this situation. There are no locks for the xrun detection between > > mmap_begin() and mmap_commit(). > > Quoting Paul: "i recall abramo saying that if the xrun happens within an > mmap_begin/commit pair, the driver can't detect it, or something like > that."
Caution here... Paul is not very accurate quoting me, I'll try to rephrase. Take as an example HW PCM case, snd_pcm_mmap_begin and commit don't enter kernel space and don't check for anything. Note also that it's very hard to know if an xrun is actually happened or not. We might use a conservative approach (i.e. all frames are considered written on buffer only at commit call) a less severe one (i.e. all frames are considered written at begin call), or a mixed approach. Current assumption is that between snd_pcm_avail_update call and snd_pcm_mmap_commit we always put more data than hardware can read (playback case) Of course preemption can give us surpries, but that's life... -- Abramo Bagnara mailto:[EMAIL PROTECTED] Opera Unica Phone: +39.546.656023 Via Emilia Interna, 140 48014 Castel Bolognese (RA) - Italy ALSA project http://www.alsa-project.org It sounds good! _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
