linux alsa机制学习笔记1

Linux 音频 ALSA 机制学习笔记<一>

首先宏观看内核暴露给上层的接口：

root@android:/ # cat /dev/snd/

controlC0 pcmC0D10p pcmC0D13c pcmC0D15c pcmC0D2c pcmC0D3c pcmC0D5p pcmC0D8c

pcmC0D0c pcmC0D11p pcmC0D13p pcmC0D15p pcmC0D2p pcmC0D3p pcmC0D6c pcmC0D9c

pcmC0D0p pcmC0D12c pcmC0D14c pcmC0D1c pcmC0D31c pcmC0D4p pcmC0D6p pcmC0D9p

pcmC0D10c pcmC0D12p pcmC0D14p pcmC0D1p pcmC0D32p pcmC0D5c pcmC0D7p timer

主要由 control 与许多 pcm 设备组成，其中控制类 control 接口是通过 get 与 put 来实现上层与内核的交互的；

.name = "MSM8960 Media1",

.stream_name = "MultiMedia1",

.cpu_dai_name = "MultiMedia1",

.platform_name = "msm-pcm-dsp",

.dynamic = 1,

.trigger = {SND_SOC_DPCM_TRIGGER_POST, SND_SOC_DPCM_TRIGGER_POST},

.codec_dai_name = "snd-soc-dummy-dai",

.codec_name = "snd-soc-dummy",

.ignore_suspend = 1,

.ignore_pmdown_time = 1, /* this dainlink has playback support */

.cpu_dai_name = "msm-dai-q6.16385",

.platform_name = "msm-pcm-routing",

.codec_name = "tabla_codec",

.codec_dai_name = "tabla_tx1",

.no_pcm = 1,

.be_id = MSM_BACKEND_DAI_SLIMBUS_0_TX,

.be_hw_params_fixup = msm_slim_0_tx_be_hw_params_fixup,

.ops = &msm_be_ops,

},

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.hw_params = msm_pcm_hw_params,

.close = msm_pcm_close,

.ioctl = snd_pcm_lib_ioctl,

.prepare = msm_pcm_prepare,

.trigger = msm_pcm_trigger,

.pointer = msm_pcm_pointer,

.mmap = msm_pcm_mmap,

};

下面重点说 kcontrol 以及如何与上层交互：

<一>直接注册 kcontrol，这类 kcontrol 重点是实现更改寄存器的值:

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};

static struct snd_soc_codec_driver soc_codec_dev_tabla = {

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.controls = tabla_snd_controls,

.num_controls = ARRAY_SIZE(tabla_snd_controls),

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