amixer （一）

amixer 是 UI 设置 alsamixer的一个命令行实现。代码参见 amixer.c

amixer -D hw:1 info 查看某卡的可控组件信息。
输出
Card hw:1 'NVidia'/'HDA NVidia at 0xdf080000 irq 17'
  Mixer name    : 'Nvidia GPU 83 HDMI/DP'
  Components    : 'HDA:10de0083,14583702,00100100'
  Controls : 28
  Simple ctrls : 4

代码
char *card = “hw:1”
snd_ctl_t *handle;
snd_ctl_open(&handle, card, 0)

snd_ctl_card_info_t *info;
snd_ctl_card_info(handle, info) 获取卡信息

printf("Card %s '%s'/'%s'\n", card, snd_ctl_card_info_get_id(info), snd_ctl_card_info_get_longname(info));
printf(" Mixer name    : '%s'\n", snd_ctl_card_info_get_mixername(info));
printf(" Components    : '%s'\n", snd_ctl_card_info_get_components(info));

snd_ctl_elem_list_t *clist;
snd_ctl_elem_list(handle, clist) 获取控制元素
printf(" Controls : %i\n", snd_ctl_elem_list_get_count(clist));
snd_ctl_close(handle);

snd_mixer_open(&mhandle, 0 /*Open mode*/) //打开一个空的混响器
snd_mixer_attach(mhandle, card) 加载一个实际的控制器
snd_mixer_selem_register(mhandle, NULL, NULL) 注册基本混响类
snd_mixer_load(mhandle) 从类中初始化一个实例出来。
printf(" Simple ctrls : %i\n", snd_mixer_get_count(mhandle)); 获取可控制项目的个数
snd_mixer_close(mhandle)

命令行 amixer -D hw:1 controls  列出所有可控项
输出
numid=1,iface=CARD,name='HDMI/DP,pcm=3 Jack'
numid=7,iface=CARD,name='HDMI/DP,pcm=7 Jack'
numid=13,iface=CARD,name='HDMI/DP,pcm=8 Jack'
numid=19,iface=CARD,name='HDMI/DP,pcm=9 Jack'
numid=2,iface=MIXER,name='IEC958 Playback Con Mask'
numid=8,iface=MIXER,name='IEC958 Playback Con Mask',index=1
numid=14,iface=MIXER,name='IEC958 Playback Con Mask',index=2
numid=20,iface=MIXER,name='IEC958 Playback Con Mask',index=3
numid=3,iface=MIXER,name='IEC958 Playback Pro Mask'
numid=9,iface=MIXER,name='IEC958 Playback Pro Mask',index=1
numid=15,iface=MIXER,name='IEC958 Playback Pro Mask',index=2
numid=21,iface=MIXER,name='IEC958 Playback Pro Mask',index=3
numid=4,iface=MIXER,name='IEC958 Playback Default'
numid=10,iface=MIXER,name='IEC958 Playback Default',index=1
numid=16,iface=MIXER,name='IEC958 Playback Default',index=2
numid=22,iface=MIXER,name='IEC958 Playback Default',index=3
numid=5,iface=MIXER,name='IEC958 Playback Switch'
numid=11,iface=MIXER,name='IEC958 Playback Switch',index=1
numid=17,iface=MIXER,name='IEC958 Playback Switch',index=2
numid=23,iface=MIXER,name='IEC958 Playback Switch',index=3
numid=6,iface=PCM,name='ELD',device=3
numid=25,iface=PCM,name='Playback Channel Map',device=3
numid=12,iface=PCM,name='ELD',device=7
numid=26,iface=PCM,name='Playback Channel Map',device=7
numid=18,iface=PCM,name='ELD',device=8
numid=27,iface=PCM,name='Playback Channel Map',device=8
numid=24,iface=PCM,name='ELD',device=9
numid=28,iface=PCM,name='Playback Channel Map',device=9

代码
char card="hw:1"
snd_hctl_t *handle;
snd_hctl_open(&handle, card, 0/*, */)
snd_hctl_load(handle) 加载所有元素 并且 拍

snd_hctl_elem_t *elem;
snd_ctl_elem_info_t *info;
snd_ctl_elem_id_t *id;

for (elem = snd_hctl_first_elem(handle); elem; elem = snd_hctl_elem_next(elem)) {
    snd_hctl_elem_info(elem, info)
    //从elem的info中可以获得如何控制此element，如
      //type=INTEGER,access=rw---R--,values=8,min=0,max=36,step=0
      //: values=0,0,0,0,0,0,0,0  (8个值  = values)
      //| container
      //| chmap-fixed=FL,FR
				
					    //type = snd_ctl_elem_type_name(snd_ctl_elem_info_get_type(info))
    //access = snd_ctl_elem_info_is_readable(info)
    //values = snd_ctl_elem_info_get_count(info) 可设置的个数
    //snd_ctl_elem_info_get_min/max/step(info)
    if (snd_ctl_elem_info_is_inactive(info))    continue;
    snd_hctl_elem_get_id(elem, id);
    str = snd_ctl_ascii_elem_id_get(id);
    if (str)
        printf("%s", str);
    free(str);
}