Re: [alsa-devel] Frame-based access (via mmap) and cross-device synchronisation

Metathronius Galabant wrote:

At any given time x0, x1, ... xn I'd like to take some kind of "snapshot" of both devices, ask them "how many frame do you have?". This MUST NOT be restricted to the period, but it should be like device1 has 80 frames, device2 only has 78 frames.

Call snd_pcm_avail(). The granlarity of its return value is device specific; e.g., chips like Emu10k1 or DS-1 move data in blocks of 256 or 512 samples, and USB uses 1-ms frames. You are not guaranteed to get a result that is more recent than the last period boundary, although most devices can do better.

Best regards, Clemens