At Mon, 19 Jan 2004 08:31:01 -0400,
Manuel Jander wrote:
>
> Hi,
>
> I'm trying to familiarize myself with the Control API (userland
> programs). I'm somewhat scared about the huge amount of API functions...
>
> I hammered some code together but i'm not very sure if i'm doing it
> right. If anyone can comment about this concept code, would be nice.
>
> What i intend to do:
>
> 1) Gain access to a control with numeric ID "CTRL_HRTF".
> 2) Read some info (value limits and such).
> 3) Write 6 (upto 112) integer values into that control.
>
> The commented code (//) are things that i believe are not needed.
>
> void test() {
> int i;
> snd_kcontrol_t *ctlp;
^^^^^^^^^^^^^^
snd_ctl_t
>
> /* Open the control. Is this really needed ? */
> if ((err = snd_ctl_open(&ctlp, "3d_hrtf", SND_CTL_ASYNC)) != 0) {
> fprintf (stderr, "3D CTL failed: (%s)\n", snd_strerror (err));
> exit(1);
> }
if you open "3d_hrtf", you have to define this in your asoundrc.
(i think it's intentional, right?)
>
> /* Retrieve some ifno to check if anything is as expected. */
> snd_ctl_elem_info_t *info;
> snd_ctl_card_info_alloca(info)
^^^^
elem
>
> /* Setup info struct. */
> //snd_ctl_elem_info_set_id(info, const snd_ctl_elem_id_t *ptr);
> snd_ctl_elem_info_set_numid(info, CTRL_HRTF);
you should use the name/index pair rather than the numid.
the number id may be changed e.g. if the driver is modified.
> snd_ctl_elem_info_set_interface(info, snd_ctl_elem_iface_t val);
> snd_ctl_elem_info_set_device(info, 0);
> snd_ctl_elem_info_set_subdevice(info, 2);
subdevice 2 ??
> //snd_ctl_elem_info_set_name(info, const char *val);
>
> /* Get info field 0. */
> snd_ctl_elem_info_set_index(info, 0);
> if ((err = snd_ctl_elem_info(ctlp, info)) != 0) {
> fprintf (stderr, "3D CTL failed: (%s)\n", snd_strerror (err));
> exit(1);
> }
> snd_ctl_elem_info_free(info);
if you call alloca, you cannot (or don't have to) free it explicitly.
> /* Declare and setup ctl_elem_value struct. */
> snd_ctl_elem_value_t *ctl_val;
> snd_ctl_elem_value_alloca(ctl_val);
>
> //snd_ctl_elem_value_set_id(ctl_val, const snd_ctl_elem_id_t *ptr);
> snd_ctl_elem_value_set_numid(ctl_val, CTRL_HRTF /* Some const defined
> elsewhere. */);
> snd_ctl_elem_value_set_interface(ctl_val, SNDRV_CTL_ELEM_IFACE_PCM);
> snd_ctl_elem_value_set_device(ctl_val, 0);
> snd_ctl_elem_value_set_subdevice(ctl_val, 2);
> //snd_ctl_elem_value_set_name(ctl_val, const char *val);
>
> /* Write values. */
> for (i=0; i<6; i++) {
> snd_ctl_elem_value_set_index(ctl_val, i);
> snd_ctl_elem_value_alloca(ctl_val);
allocate twice??
> snd_ctl_elem_value_set_integer(ctl_val, unsigned int idx, long val);
the second argument of set_integer is NOT the index of the element
itself. it's the array index of that element. (a control element is
an array of integer/boolean/etc.)
if you want to set different elements with different indices, call
snd_ctl_elem_write() in this loop.
> }
> /* Dispatch ctl write to soundcard. */
> if ((err = snd_ctl_elem_write(ctlp, &control)) != 0) {
> fprintf (stderr, "3D CTL failed: (%s)\n", snd_strerror (err));
> exit(1);
> }
> snd_ctl_elem_value_free(ctl_val);
don't free the alloca'ed record.
> }
ciao,
Takashi
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