On Fri, Jul 12, 2024 at 06:48:09PM +0900, Asahi Lina wrote:
> > For example, assuming the matrix mixer has 34 destination and 66
> > sources, they can be expressed by 34 control elements with 66 array
> > elements. A single snd_kcontrol structure can provide them, as long as
> > they have the same nature. The control elements are identified by index
> > value.
>
> It took me a while to understand what you meant here, but I think I get
> it: Using a single snd_kcontrol for the entire mixer, with 34 indexed
> elements each taking 66 array values, right?
This is rough example for the above idea.
```
static int info_cb(struct snd_kcontrol *kctl, struct snd_ctl_elem_info *einfo)
{
einfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
einfo->count = 66; // up to 128 for integer value array.
einfo->value.integer.min = 0; // note long type, varies between
// ILP32/LP64 data models.
einfo->value.integer.max = 256; // ditto.
einfo->value.integer.step = 1; // ditto.
return 0;
}
static int get_cb(struct snd_kcontrol *kctl, struct snd_ctl_elem_value *uval)
{
unsigned int index = snd_ctl_get_ioff(kctl, &info->id);
// Any operation according to the index of control elements in the set.
return 0;
}
static int put_cb(struct snd_kcontrol *kctl, struct snd_ctl_elem_value *uval)
{
unsigned int offset = snd_ctl_get_ioff(kctl, &info->id);
// Any operation according to the index of control elements in the set.
return 0;
}
int add_control_elements(struct my_data *my_data)
{
// Emulate AK4396.
// 20 * log10(x/255) (dB)
// Here, x is written value.
//
// Some examples in:
// https://github.com/alsa-project/alsa-lib/blob/master/test/user-ctl-element-set.c.
static const SNDRV_CTL_TLVD_DECLARE_DB_LINEAR(range_tlv, -4813, 0);
static const struct snd_kcontrol_new template = {
. iface = SNDRV_CTL_ELEM_IFACE_MIXER,
.device = 10,
.subdevice = 20,
.name = "multiplexer",
.index = 0,
// I guess any operation on ARC USB does not control the hardware directly unlike RC and
// ARC, thus SNDRV_CTL_ELEM_ACCESS_VOLATILE is not required.
.access = SNDRV_CTL_ELEM_ACCESS_READWRITE | SNDRV_CTL_ELEM_ACCESS_TLV_READ,
.count = 34, // The total number of control elements in the set.
.info = info_cb,
.get = get_cb,
.put = pub_cb,
.tlv.p = &range_tlv,
};
struct snd_kcontrol *kctl = snd_ctl_new1(&template, my_data);
err = snd_ctl_add(my_data->card, kctl);
...
}
```
> How do these kinds of controls show up in alsamixer and other userspace
> mixer tools? Are they usable at all, or just with low-level access via
> amixer/alsactl?
These control elements can be enumerated and operated as usual, just
have the sequential value in index (and numid) field in element
identifier.
```
$ amixer -c 0 controls
...
numid=16,iface=MIXER,name='multiplexer',device=10,subdevice=20
numid=17,iface=MIXER,name='multiplexer',index=1,device=10,subdevice=20
numid=18,iface=MIXER,name='multiplexer',index=2,device=10,subdevice=20
numid=19,iface=MIXER,name='multiplexer',index=3,device=10,subdevice=20
numid=20,iface=MIXER,name='multiplexer',index=4,device=10,subdevice=20
numid=21,iface=MIXER,name='multiplexer',index=5,device=10,subdevice=20
numid=22,iface=MIXER,name='multiplexer',index=6,device=10,subdevice=20
numid=23,iface=MIXER,name='multiplexer',index=7,device=10,subdevice=20
numid=24,iface=MIXER,name='multiplexer',index=8,device=10,subdevice=20
numid=25,iface=MIXER,name='multiplexer',index=9,device=10,subdevice=20
...
```
Of cource, these is no integrations in any type of alsa-lib mixer API
abstractions. I use Quasmixer in quastools project to operate them.
* https://gitlab.com/sebholt/qastools
Regards
Takashi Sakamoto
