Chris Cannam wrote: > While trying to track down the source of some poor timing in > sequencing, I've noticed that my ALSA sequencer queue timer has a > tendency to fall suddenly behind. > > I have a little test program (available on request) that just starts a > queue and every second or so compares the queue timer against real > time as returned by gettimeofday(). It doesn't mind if the two don't > quite match, but it does complain if the difference between the two > timers changes dramatically between two sample points. When I run > it, it never lasts for more than about a minute before the ALSA queue > timer suddenly slips by anything from 10 to 60 milliseconds.
Please, send me your test program. > This is a non-low-latency kernel so I'm not surprised that there may > be some occasional timing issues, but 60ms is a lot on an unloaded > machine, and I am vaguely surprised that the timer doesn't notice > it's fallen behind and recover -- instead all events on the queue > continue to be delivered late forever. This obviously makes for some > disconcerting audible effects. > > The system is SuSE 9.0 on a dual 2GHz Athlon using SuSE's stock SMP > kernel. I have tried both ALSA 0.9.6 (from SuSE) and 1.0.0rc2 > drivers and libraries. I haven't managed to reproduce it using a > PlanetCCRMA SMP kernel on the same machine, nor on my uniprocessor > laptop. I've surveyed a few other people on rosegarden-devel and > nobody's corroborated my findings, so I guess it might be related to > using a dual-processor machine. > > Any thoughts on this, anyone? I'm finding it a little depressing that > I can't play even a minute of 4/4 beats from an ALSA test program > without the timing slipping audibly at least once. I'm ready to > delve cluelessly into the timer code to take a look, but (glancing at > alsa-kernel/core/timer.c) I'm not at all sure how far I'd get... The ALSA MIDI sequencer can use several timer sources. By default, it uses the Linux system timer functions, see: http://hegel.ittc.ukans.edu/topics/linux/man-pages/man9/init_timer.9.html Other timer sources are PCM devices and the RTC timer. The module snd-rtctimer provides this functionality. To compile it for a 2.4.x kernel, you need to patch your rtc driver (and rebuild), see alsa-driver/utils/patches You can set a system-wide alternate timer in your /etc/modules.conf, for instance: options snd-seq seq_default_timer_device=1 alias snd-timer-1 snd-rtctimer Or your program can select an alternate timer source for a single queue. See: http://www.mail-archive.com/[EMAIL PROTECTED]/msg09048.html Regards, Pedro -- ALSA Library Bindings for Pascal http://alsapas.alturl.com ------------------------------------------------------- This SF.net email is sponsored by: SF.net Giveback Program. Does SourceForge.net help you be more productive? Does it help you create better code? SHARE THE LOVE, and help us help YOU! Click Here: http://sourceforge.net/donate/ _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
