On Mon, 30 Sep 2002, Jaroslav Kysela wrote: > > me directly that - the current position in the buffer?) I can calculate when > > the required position _will_ happen. So I can just schedule the timer or sleep > > until that time. When it arrives I can check again snd_pcm_avail_update to see > > whether my calculation way correct and adjust the sleep period. > > > > I do not understand why ALSA drivers (or at least some plug-ins) could not do > > the same? > > What same? Offer position in ring buffer?
No, I ment, use the timing information to wake up application ealier if the period interrupt is too long. > Use snd_pcm_status() to get the accurate timing information. The > avail_update function is light version which does not need a context > switch between user and kernel space. Thank you. This is a very valuable information. I was mislead by this "_update" and I have thought that it will query the card. The documentation says "The function snd_pcm_avail_update updates (! here should be written: reads, not updates) the current available count of samples for writing (playback) or filled samples for reading (capture). ". And may be "Obtaining fast device status" should be changed to ""Obtaining device status fast" and written clearly that avail_update will in fact only read the number. BTW. I have just read (alsa-lib DOC) that snd_pcm_avail_update should always return a positive number when there is no error. But unfortunately there is a bug in alsa-lib in snd_pcm_mmap_playback_avail and snd_pcm_mmap_capture_avail (src/pcm/pcm_local.h) which may cause a negative value to be returned. Just think what could happen if the initial avail is not only < 0 , but avail < pcm->boundary as well. Then avail+pcm->boundary < 0 still. This may happen if pcm->appl.ptr is not updated (I want the card to just play/record all the time independent whether my application cares or not at the moment). No underruns. This works, but I had to check for negative values coming out of avail_update. This should be at least documented (fixing will not be as easy as I have initially thought). Best regards, -- Tomasz Motylewski ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
