Re: [LAD] ALSA doumentation

On Fri, Nov 14, 2008 at 10:31:14AM +0100, Clemens Ladisch wrote:

> > Is there, after X years of ALSA, any documentation that
> > explains the basic concepts and tells me how to do this ?
>
> No.

Thanks for the confirmation, and for the example code.

The first ever LAC lecture I attended was Takashi
introducing ALSA at the first conference.

I'd like to invite those who know more to present a
paper / workshop on the subject at LAC 2009...

 
> > how I can e.g. set the sample clock source on a RME MADI card
> > in less than ten lines of C code
>
> system("amixer cset name='Sample Clock Source' 3");

:-)

> #include <stdio.h>
> #include <stdlib.h>
> #include <alsa/asoundlib.h>
>
> static void check(int err, const char *f)
> {
> if (err < 0) {
> fprintf(stderr, "%s failed: %s\n", f, snd_strerror(err));
> exit(EXIT_FAILURE);
> }
> }
> #define CHECK(f) check(f, #f)
>
> int main()
> {
> snd_ctl_t *ctl;
> snd_ctl_elem_value_t *value;
>
> CHECK(snd_ctl_open(&ctl, "default", 0));
>
> snd_ctl_elem_value_alloca(&value);
> snd_ctl_elem_value_set_interface(value, SND_CTL_ELEM_IFACE_MIXER);
> snd_ctl_elem_value_set_name(value, "Sample Clock Source");
> snd_ctl_elem_value_set_enumerated(value, 0, 3); /* 3: 48 kHz */
> CHECK(snd_ctl_elem_write(ctl, value));
>
> snd_ctl_close(ctl);
> return 0;
> }

So it's actually quite simple (in this case -- I imagine there are
more complex things as well, if not why does the API have a zillion
functions). The problem is that starting from the existing docs it's
near impossible to find out even these simple things.

One mor question: is there a way to obtain a 'handle' on a
control element so it can be updated frequently without the
overhead of textual encoding and decoding each time ?

Ciao,

-- 
FA
Laboratorio di Acustica ed Elettroacustica
Parma, Italia
Lascia la spina, cogli la rosa.
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