[alsa-devel] mm functions vs. normal IO
clemens at ladisch.de
Tue Mar 4 08:58:47 CET 2008
> I was astonished that a simple wav playback example does not exist.
The alsa-lib package has test/pcm_min.c.
> What should be used:
> (I think snd_pcm_mmap_writei is the same with an additional copy behind ?)
snd_pcm_mmap_writei is the same as calling snd_pcm_mmap_begin, copying
into the buffer, and calling snd_pcm_mmap_commit.
> or snd_pcm_writei
If you have to ask, use snd_pcm_writei.
> I think mmap will have better performance,
Only if the program generates samples on the fly and can write them
directly to the buffer in a format supported by the hardware.
If you already have the data in some buffer, copying it into the
device's buffer with snd_pcm_writei or snd_pcm_mmap_writei is just as
fast as when you copy it into the device's buffer by yourself.
> but will it work with all soundcards?
Not directly. ALSA has mmap emulation for cards that don't support it.
And there are devices where only support mmap access is
> I'am also looking for a function to get the number of played frames.
ALSA doesn't count them. This is nothing that a program couldn't do
trivially by itself.
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