Control API, help

[Manuel Jander <manuel.jander@mat.utfsm.cl>]

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;
	
  /* 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);
  }
  
  /* Retrieve some ifno to check if anything is as expected. */
  snd_ctl_elem_info_t *info;
  snd_ctl_card_info_alloca(info)
	
  /* 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);
  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);
  //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);
	
  /* 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);
    snd_ctl_elem_value_set_integer(ctl_val, unsigned int idx, long val);
  }
  /* 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);
}

Thank you very much.

-- 
Manuel Jander
mjander(at)users(dot)sourceforge(dot)net



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