alsa（asoc dapm）框架分析

1 开始之前.......................................................................................................................................3

1.1 目的前提............................................................................................................................3

1.2 说明....................................................................................................................................3

1.3 版权声明............................................................................................................................3

2 alsa_amixer ....................................................................................................................................4

3 mixer control..................................................................................................................................5

3.1 snd_kcontrol_new...............................................................................................................5

3.2 kcontrol宏 ...........................................................................................................................6

3.3 kcontrol触发过程 ...............................................................................................................8

5.3.3.1 path的概念.............................................................................................20

5.3.3.3 路径定义.................................................................................................21

5.3.4 将controls、widgets、route串联起来.........................................................22

5.4 dapm kcontrol建立过程....................................................................................................23

5.4.1 接口函数.............................................................................................................23

6.2 认识plugin hooks.............................................................................................................27

6.3 配置audio paths ...............................................................................................................29

7 DAPM之四：dapm机制深入分析（上）.....................................................................................31

7.1 最小化音频子系统的能耗..............................................................................................31

7.1.1 endpoint的概念.................................................................................................31

7.1.2 complete path的概念.......................................................................................32

7.1.3 path的连接状态.................................................................................................32

8 DAPM之五：dapm机制深入分析（下）.....................................................................................42

8.2 dapm_power_widgets .......................................................................................................42

8.3 dapm_seq_run...................................................................................................................46

搭建和选择（相信这部分对于大家来说更有应用意义）。在 dapm 机制深入分析中，会展现

这两个基本音频调试工具。

1.2 说明

dapm 除了动态音频电源管理外，还肩负了音频路径建立的重任。下文会先阐述音频路径，

1.3 版权声明

关于版权问题，欢迎转载，但请注明作者和来源，如下：

BLOG :

如有纠错、疑问、建议，feel free to contact me，谢谢！

控制。因此，alsa_amixer 是音频驱动开发中的常用工具。其用法是相当简单的，如下：

~ # alsa_amixer help

Usage: amixer <options> [command]

Available options:

-h,--help this help

-c,--card N select the card

-D,--device N select the device, default 'default'

-s,--stdin Read and execute commands from stdin sequentially

Available commands:

scontrols show all mixer simple controls

scontents show contents of all mixer simple controls (default command)

sset sID P set contents for one mixer simple control

sget sID get contents for one mixer simple control

controls show all controls for given card

contents show contents of all controls for given card

cset cID P set control contents for one control

例如，我们知道一个 numid=3,iface=MIXER,name='Playback Volume'的 mixer control，该

control 用于调整回放音量，对这个 control 设置值 100，则有：

amixer cset numid=3,iface=MIXER,name='Playback Volume' 100

amixer cset numid=3 100

amixer cset name='Playback Volume' 100

以上三种方法都可以的，对于参数 cID，只提供 numid 或 name 都可以找到正确的底层的

kcontrol。

从而读写 CODEC 相关寄存器。kcontrol 主要用于 mixer（故称为 mixer control）,用

snd_kcontrol_new 结构体描述。

注：kcontrol 是 kernel control 的简称，即内核态的控制接口；代码中还会发现有 ucontrol，

这是 user control 的简称，保存用户层传递进来的参数。