通话的时候，需要打开音频通路，音频设备（上下行都要）
我们从这里开始：
packages/apps/Bluetooth/src/com/android/bluetooth/hfpclient
// in Connected state
private void processAudioEvent(int state, BluetoothDevice device) {
...
switch (state) {
...
case HeadsetClientHalConstants.AUDIO_STATE_CONNECTED:
routeHfpAudio(true);
}
}
private void acceptCall(int flag) {
...
if (flag == BluetoothHeadsetClient.CALL_ACCEPT_HOLD) {
// When unholding a call over Bluetooth make sure to route audio.
routeHfpAudio(true);
}
...
}两种场景，一个是接通电话，一个是电话hold之后，unhold的时候。都需要去调用routeHfpAudio(true).我们简化问题，只分析打开的情况。
static synchronized void routeHfpAudio(boolean enable) {
...
if (enable && !sAudioIsRouted) {
sAudioManager.setParameters("hfp_enable=true");
} else if (!enable) {
sAudioManager.setParameters("hfp_enable=false");
}
...
}直接跳过中间繁琐的调用分析，欢迎查看我之前的博客。我们直接来到这里（路径都懒得贴了，搞audio的都知道）：
audio_hw.c
static int adev_set_parameters(struct audio_hw_device *dev, const char *kvpairs)
{
...
struct str_parms *parms;
...
//一猜就是通过等号把上面传下来的参数分割成对:hfp_enable,true
parms = str_parms_create_str(kvpairs);
...
status = audio_extn_set_parameters(adev, parms);
...
}hardware/qcom/audio/hal/audio_extn/audio_extn.c
int audio_extn_set_parameters(struct audio_device *adev,
struct str_parms *parms)
{
...
ret = audio_extn_hfp_set_parameters(adev, parms);
...
}hardware/qcom/audio/hal/audio_extn/hfp.c
int audio_extn_hfp_set_parameters(struct audio_device *adev, struct str_parms *parms)
{
...
//解析字符串参数
ret = str_parms_get_str(parms, AUDIO_PARAMETER_HFP_ENABLE, value,
sizeof(value));
if (ret >= 0) {
if ((!strncmp(value,"true",sizeof(value))) && (!hfpmod.is_hfp_running))
ret = start_hfp(adev,parms);
else if((!strncmp(value,"false",sizeof(value))) && (hfpmod.is_hfp_running))
stop_hfp(adev);
else {
...
}
}
...
//设置routing
ret = str_parms_get_str(parms, AUDIO_PARAMETER_STREAM_ROUTING,
value, sizeof(value));
if (ret >= 0) {
val = atoi(value);
if (val > 0)
select_devices(adev, hfpmod.ucid);
}
//设置hfp_volume
memset(value, 0, sizeof(value));
ret = str_parms_get_str(parms, AUDIO_PARAMETER_KEY_HFP_VOLUME,
value, sizeof(value));
if (ret >= 0) {
...
hfp_set_volume(adev, vol);
}
}也就是说routeHfpAudio的调用，最终对应着start_hfp和stop_hfp.
这里我们就看看start_hfp就好。
static int32_t start_hfp(struct audio_device *adev,
struct str_parms *parms __unused)
{
...
//直接来个usecase
struct audio_usecase *uc_uplink_info;
uc_uplink_info = (struct audio_usecase *)calloc(1, sizeof(struct audio_usecase));
//初始化
uc_uplink_info->id = hfpmod.ucid;
uc_uplink_info->type = PCM_HFP_CALL;
uc_uplink_info->stream.out = adev->primary_output;
uc_uplink_info->devices = adev->primary_output->devices;
uc_uplink_info->in_snd_device = SND_DEVICE_NONE;
uc_uplink_info->out_snd_device = SND_DEVICE_NONE;
list_add_tail(&adev->usecase_list, &uc_uplink_info->list);
//hfpmod.ucid 的值为
//USECASE_AUDIO_HFP_SCO_UPLINK(hfp_sco的上行链路的usecase)
//用这个usecase去选出设备
select_devices(adev, hfpmod.ucid);
...
//获取pcm设备id
//上行 rx
pcm_ul_rx_id = platform_get_pcm_device_id(uc_uplink_info->id, PCM_PLAYBACK);
//上行 tx
pcm_ul_tx_id = platform_get_pcm_device_id(uc_uplink_info->id, PCM_CAPTURE);
pcm_dl_rx_id = platform_get_pcm_device_id(uc_downlink_info.id, PCM_PLAYBACK);
pcm_dl_tx_id = platform_get_pcm_device_id(uc_downlink_info.id, PCM_CAPTURE);
...
//打开上行tx对应的pcm(一般是mic)
hfpmod.hfp_ul_tx = pcm_open(adev->snd_card,
pcm_ul_tx_id,
PCM_IN, &pcm_config_hfp);
...
//另外三个打开操作类似
}audio_hw.c中可以查到：
USECASE_AUDIO_HFP_SCO_UPLINK对应的use_case_table名字:"hfp-sco"
platform.c中可以查到:
USECASE_AUDIO_HFP_SCO_UPLINK对应的hw_interface_table名字:
"QUAT_TDM_TX_0"
这些对应的mixer_paths.xml中都有:
<path name="hfp-sco">
<ctl name="QUAT_TDM_RX_2 Audio Mixer MultiMedia21" value="1" />
<ctl name="MultiMedia21 Mixer AUX_PCM_UL_TX" value="1" />
<ctl name="AUX_PCM_RX Audio Mixer MultiMedia6" value="1" />
<ctl name="MultiMedia6 Mixer QUAT_TDM_TX_0" value="1" />
</path>还有这个pcm_config_hfp的定义:
static struct pcm_config pcm_config_hfp = {
.channels = 1,
.rate = 8000,
.period_size = 240,
.period_count = 2,
.format = PCM_FORMAT_S16_LE,
.start_threshold = 0,
.stop_threshold = INT_MAX,
.avail_min = 0,
};估计普通电话也差不多，单声道，8k采样率（窄带，宽带是这个:
USECASE_AUDIO_HFP_SCO_WB_UPLINK），格式:PCM_FORMAT_S16_LE.
到这里为止，pcm设备就准备完毕，可以使用了！
那是什么时候开始使用这个pcm设备，调用pcm_read和pcm_write的呢？全局搜索了一遍也没看到，也没去调用audio_hw里的out_write!!!!.又仔细看了一遍start_hfp，难道是它：
static int32_t start_hfp(struct audio_device *adev,
struct str_parms *parms __unused)
{
...
hfpmod.hfp_ul_tx = pcm_open(adev->snd_card,
pcm_ul_tx_id,
PCM_IN, &pcm_config_hfp);
...
if (pcm_start(hfpmod.hfp_ul_rx) < 0) {
ALOGE("%s: pcm start for hfp ul rx failed", __func__);
ret = -EINVAL;
goto exit;
}
...
}这个过程中，总共pcm_open了四个设备:
hfpmod.hfp_ul_rx
hfpmod.hfp_ul_tx
hfpmod.hfp_dl_rx
hfpmod.hfp_dl_tx
然后pcm_start了这四个FE(前端) PCM.
tinymix中可以看到打开的通路有这些:
637 BOOL 1 QUAT_TDM_TX_0 Audio Mixer MultiMedia6 On
684 BOOL 1 QUAT_TDM_RX_2 Audio Mixer MultiMedia21 On
879 BOOL 1 MultiMedia6 Mixer QUAT_TDM_TX_0 On
987 BOOL 1 MultiMedia21 Mixer AUX_PCM_UL_TX On
1027 BOOL 1 AUX_PCM_RX Audio Mixer MultiMedia6 On第一路:"QUAT_TDM_TX_0 Audio Mixer MultiMedia6"
FE（前端）是MultiMedia6,BE（后端）是QUAT_TDM_TX_0，Audio Mixer表示DSP路由功能。
未完待续。。。