本文主要是簡略的介紹下移植的過程
1.Alsa主要包括3個文件夾
haraware/alsa_sound 硬件抽象層部分
external\alsa-lib 主要是提供一些音頻庫
external\alsa-utils 工具部分，配合調試之類的，可以不用
2.獲取源碼的方式：
首先，cd到Android源碼樹根目錄下：
cd /home/***/gin:
1).從Android主頁下載ALSA聲卡的相關源碼：
git clone git://android.git.kernel.org/platform/external/alsa-lib.git
git clone git://android.git.kernel.org/platform/external/alsa-utils.git
git clone git://android.git.kernel.org/platform/hardware/alsa_sound.git
這樣下載完之後的各個包將會自動放到合適的地方。
2).一般的源碼包裏面可能自帶了ALSA這幾個包，最好使用原有的包，這些包是經過廠商的修改會減少很多問題。
之前我使用方式1，直接git clone了這幾個包，結果使用中出現了問題，登錄優酷網頁播放視頻的時候會一卡一卡的現象，停頓時間很頻繁，聲音畫面完全不同步，最好不得不放棄使用ALSA。是由於ALSA導致的，一時不知道怎麼修改，這個修改我隨後會發出來。
3.開始配置：
1）首先配置BoardConfig.mk
這個文件裏面有2個地方
a.BOARD_USES_ALSA_AUDIO := true 主要是宏定義，切換使用到ALSA
BUILD_WITH_ALSA_UTILS := true
b.打開3G模塊的文件系統配置，這個根據不同的需求配置不同，各人看情況而定。
2）將第一步裏面的3個包放到指定的位置。
大部分情況下external\alsa-lib及external\alsa-utils 不需要改動，直接使用即可。但是haraware/alsa_sound 有時候還是需要有所改動的。
因爲android支持的設備有以下一些：
enum audio_devices {
// output devices
DEVICE_OUT_EARPIECE = 0x1,
DEVICE_OUT_SPEAKER = 0x2,
DEVICE_OUT_WIRED_HEADSET = 0x4,
DEVICE_OUT_WIRED_HEADPHONE = 0x8,
DEVICE_OUT_BLUETOOTH_SCO = 0x10,
DEVICE_OUT_BLUETOOTH_SCO_HEADSET = 0x20,
DEVICE_OUT_BLUETOOTH_SCO_CARKIT = 0x40,
DEVICE_OUT_BLUETOOTH_A2DP = 0x80,
DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES = 0x100,
DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER = 0x200,
DEVICE_OUT_AUX_DIGITAL = 0x400,
DEVICE_OUT_DEFAULT = 0x8000,
DEVICE_OUT_ALL = (DEVICE_OUT_EARPIECE | DEVICE_OUT_SPEAKER | DEVICE_OUT_WIRED_HEADSET |
DEVICE_OUT_WIRED_HEADPHONE | DEVICE_OUT_BLUETOOTH_SCO | DEVICE_OUT_BLUETOOTH_SCO_HEADSET |
DEVICE_OUT_BLUETOOTH_SCO_CARKIT | DEVICE_OUT_BLUETOOTH_A2DP | DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |
DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER | DEVICE_OUT_AUX_DIGITAL | DEVICE_OUT_DEFAULT),
DEVICE_OUT_ALL_A2DP = (DEVICE_OUT_BLUETOOTH_A2DP | DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |
DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER),
// input devices
DEVICE_IN_COMMUNICATION = 0x10000,
DEVICE_IN_AMBIENT = 0x20000,
DEVICE_IN_BUILTIN_MIC = 0x40000,
DEVICE_IN_BLUETOOTH_SCO_HEADSET = 0x80000,
DEVICE_IN_WIRED_HEADSET = 0x100000,
DEVICE_IN_AUX_DIGITAL = 0x200000,
DEVICE_IN_VOICE_CALL = 0x400000,
DEVICE_IN_BACK_MIC = 0x800000,
DEVICE_IN_DEFAULT = 0x80000000,
DEVICE_IN_ALL = (DEVICE_IN_COMMUNICATION | DEVICE_IN_AMBIENT | DEVICE_IN_BUILTIN_MIC |
DEVICE_IN_BLUETOOTH_SCO_HEADSET | DEVICE_IN_WIRED_HEADSET | DEVICE_IN_AUX_DIGITAL |
DEVICE_IN_VOICE_CALL | DEVICE_IN_BACK_MIC | DEVICE_IN_DEFAULT)
};
但是有時候像平板部分是沒有聽筒的，所以需要在alsa_default.cpp文件裏static status_t s_open(alsa_handle_t *handle, uint32_t devices, int mode)函數裏修改
if (devices == AudioSystem::DEVICE_OUT_EARPIECE) {
devices = AudioSystem::DEVICE_OUT_SPEAKER;
}
即：如果是聽筒的話，直接設置爲喇叭設備，強制設置，呵呵，這個有點不地道，但是修改方式簡單快捷。
3）.修改asound.conf
# Android ALSA configuration file for TI OMAP3430 reference platform using the TWL4030 ASoC audio.
##
## Mixer Devices
##
ctl.AndroidOut{
type hw
card 0
}
ctl.AndroidIn{
type hw
card 0
}
ctl.AndroidPlayback {
type hw
}
ctl.AndroidRecord {
type hw
}
##
## # Speaker
##
pcm.AndroidPlayback_Speaker_normal {
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'Speaker Playback Switch'
value [1 1]
}
{
name 'Speaker Playback Volume'
value [4 4]
}
]
}
}
pcm.AndroidPlayback_Speaker_incall{
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'Speaker incall Switch'
value [1 1]
}
{
name 'Speaker incall Volume'
value [2 2]
}
{
name 'MIC1 Mode Control'
value 1
}
{
name 'MIC1 Boost'
value 4
}
]
}
}
pcm.AndroidPlayback_Speaker_ringtone{
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'Speaker ringtone Switch'
value [1 1]
#value "on"
}
{
name 'Speaker ringtone Volume'
value [4 4]
}
]
}
}
##
## # Headset
##
pcm.AndroidPlayback_Headset_normal {
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'HP Playback Switch'
value [1 1]
}
{
name 'Speaker Playback Switch'
value [0 0]
}
{
name 'HP Playback Volume'
value [4 4]
}
]
}
}
pcm.AndroidPlayback_Headset_incall{
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'Headset incall Switch'
value [1 1]
}
{
name 'Headset incall Volume'
value [6 6]
}
{
name 'MIC2 Capture Switch'
value 1
}
{
name 'MIC2 Boost'
value 4
}
]
}
}
pcm.AndroidPlayback_Speaker_Headset_ringtone{
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'Speaker ringtone Switch'
value [1 1]
}
{
name 'Speaker ringtone Volume'
value [4 4]
}
{
name 'Headset incall Switch'
value [1 1]
}
{
name 'Headset incall Volume'
value [6 6]
}
]
}
}
pcm.AndroidPlayback_Speaker_Headset_normal {
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'Headset ringtone Switch'
value 0
}
]
}
}
##
## # AndroidCapture
##
pcm.AndroidCapture {
type hooks
slave.pcm {
type hw
card 0
device 0
}
hooks.0 {
type ctl_elems
hook_args [
{
name 'MIC1 Capture Switch'
value 1
}
{
name 'MIC1 Boost'
value 4
}
{
name 'MIC2 Capture Switch'
value 1
}
{
name 'MIC2 Boost'
value 4
}
]
}
}
這個和內核裏面的soc系統是相關的，是必須和內核的路由結合起來配置，否則肯定出問題。
這裏貼出內核的對應配置：
static const struct snd_kcontrol_new rt5631_snd_controls[] = {
SOC_DOUBLE("Speaker Playback Switch", RT5631_SPK_OUT_VOL,15, 7, 1, 1),
SOC_DOUBLE("Speaker Playback Volume", RT5631_SPK_OUT_VOL, 8, 0, 27, 0),
SOC_DOUBLE("Speaker incall Switch", RT5631_SPK_OUT_VOL,15, 7, 1, 1),
SOC_DOUBLE("Speaker incall Volume", RT5631_SPK_OUT_VOL, 8, 0, 27, 0),
SOC_SINGLE("MIC1 Capture Switch", RT5631_MIC_CTRL_1, 15, 1, 1),
SOC_SINGLE("MIC1 Boost", RT5631_MIC_CTRL_2, 12, 9, 0),
SOC_DOUBLE("Speaker ringtone Switch", RT5631_SPK_OUT_VOL,15, 7, 1, 1),
SOC_DOUBLE("Speaker ringtone Volume", RT5631_SPK_OUT_VOL, 8, 0, 24, 0),
SOC_DOUBLE("HP Playback Switch", RT5631_HP_OUT_VOL,15, 7, 1, 1),
SOC_DOUBLE("HP Playback Volume", RT5631_HP_OUT_VOL, 8, 0, 63, 1),
SOC_DOUBLE("Headset incall Switch", RT5631_HP_OUT_VOL,15, 7, 1, 1),
SOC_DOUBLE("Headset incall Volume", RT5631_HP_OUT_VOL, 8, 0, 63, 1),
SOC_SINGLE("MIC2 Capture Switch", RT5631_MIC_CTRL_1, 7, 1, 1),
SOC_SINGLE("MIC2 Boost", RT5631_MIC_CTRL_2, 8, 9, 0),
SOC_DOUBLE("Headset ringtone Switch", RT5631_HP_OUT_VOL,15, 7, 1, 1),
SOC_DOUBLE("Headset ringtone Volume", RT5631_HP_OUT_VOL, 8, 0, 63, 1),
}
只要文件系統裏面的路由和內核裏面的路由完全匹配，那剩下的就是設置codec的具體信息了，這裏不解釋了
4.如果要在內核裏面查看具體的路由信息，可以到soc-core.c 文件裏面int snd_soc_put_volsw(struct snd_kcontrol *kcontrol,
struct snd_ctl_elem_value *ucontrol)函數去打印kcontrol->id.name這個實時的打印即爲當前的路由信息，不過這個信息也是你之前在rt5631_snd_controls[] 裏面註冊的信息。