On Sunday 28 July 2002 14.40, you wrote: > Anders Torger wrote: > >On Saturday 27 July 2002 17.18, you wrote: > >> Anders Torger wrote: > >> >Does anyone have any comments on this? Is repeatable exact > >> > I/O-delay possible to achieve today with current hardware (and > >> > ALSA)? > >> > >> It is the normal mode of operation for memory-mapped IO. > > > >Is it really? How do I trigger play exactly X samples after I > > trigger capture? To copy samples exactly X samples into a buffer is > > simple, the problem is to tell the sound card to synchronise the > > playback ptr with the capture ptr, that is "start running the > > playback ptr exactly X samples after the capture ptr started". The > > window of X samples is then used by the software to do its magic. > > The way you'd do this is to link the capture and playback streams of > the device you use with snd_pcm_link(). They will start together and > stay in sync (unless the hardware is broken by design). Instead of > starting playback exactly 4096 frames later, you prime the playback > stream with 4096 silent frames before starting it. At the first > interrupt issued, there will be 2048 frames to be read from the > capture stream and 2048 to write to playback. You'd read the input > signal, write another 2048 silent frames, and from the next interrupt > on you'll always have 2048 frames of processed signal to write, and > 2048 input frames to feed to the FIR.
Thanks. I'll try this. Not only the hardware can be broken, but also the driver I suppose. It seems like not all have support for snd_pcm_link(), for example my driver for RME96 (I have to do some maintenance work on that soon). > Implementing memory-mapped IO isn't exactly what you do in a day. > jackit.sf.net or the shortly-to-be-released library I'm working on > will do it for you. Just replace 'interrupt' above with a 'process' > callback and you don't have to care about the exact workings of > mmap'd ALSA at all. This is great, but I don't see why this particular thing would require memory-mapped I/O. If one makes sure to write 4096 silent frames first start playback/capture using snd_pcm_link(), it should work with snd_pcm_read/write too, shouldn't it? /Anders Torger ------------------------------------------------------- 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
