我們這裏以rk3399 android7.1平臺爲例,淺析adc接口實現檢測耳機的拔插動作。
硬件原理部分:耳機插入把PHE_DET1處的彈片彈開,然後實現headphone_dect直接連通到1.8v,檢測端得到高電平1.8v;拔出耳機,彈片回去,只有0.159v電壓。所以實現了沒有耳機插入時這個“ADC_IN4”爲低電位,插入耳機時這個“ADC_IN4”爲高電位
耳機實物圖:
軟件實現部分:
1、kernel
+ //dts配置
+ rockchip_headset {
+ compatible = "rockchip_headset";
+ io-channels = <&saradc 4>; //硬件上接的是adc4
+ io-channel-names = "headset";
+ status = "okay";
+ };
驅動:
drivers/headset_observe/rk_headset_irq_hook_adc.c
drivers/headset_observe/rockchip_headset_core.c
驅動代碼裏probe首先註冊switch這個子類,並提供switch_dev_register這個註冊入口,對應的設備驅動調用switch_dev_register把自己註冊在switch這個子類中,ret = switch_dev_register(&switch_data_headset->sdev);然後在/sys/class/switch目錄中就會生成h2w這個子目錄,裏面會有state,name等一些成員,然後初始化一個工作隊列,設置一個時間,循環去執行工作隊列去讀取ADC 的值,根據讀到的值調用switch_set_state函數改變state狀態值,然後上層通過讀取這個節點的值來相應切換狀態。
文件:./drivers/headset_observe/rockchip_headset_core.c
rockchip_headset_of_match的compatible跟dts的compatible匹配
--> 執行rockchip_headset_probe
-->kzalloc(sizeof(struct rk_headset_pdata), GFP_KERNEL); //分配內存給私有結構體rk_headset_pdata
-->ret = of_get_named_gpio_flags(node, "headset_gpio", 0, &flags); //解析gpio
如果解析到gpio就devm_gpio_request //申請GPIO,gpio_direction_input//設置GPIO口爲輸入狀態
-->of_get_named_gpio_flags(node, "hook_gpio", 0, &pdata->hook_gpio); //解析GPIO
如果解析不到GPIO就 pdata->chan = iio_channel_get(&pdev->dev, NULL); //獲取ADC通道
-->if(pdata->chan != NULL) //如果獲取到ADC channel就執行ADC檢測耳機拔插的probe探測函數
-->ret = rk_headset_adc_probe(pdev,pdata);
-->否則就執行ret = rk_headset_probe(pdev,pdata); //GPIO檢測耳機拔插模式的probe探測函數
文件:drivers/headset_observe/rk_headset_irq_hook_adc.c
//宏定義上報給上層的state值
+#define BIT_HEADSET (0 << 1) //no headphone insertion
+#define BIT_HEADSET_MIC (1 << 0) //have mic headphone insertion
+#define BIT_HEADSET_NO_MIC (1 << 1) //no mic headphone insertion
rk_headset_adc_probe
->ret = switch_dev_register(&headset->sdev); //註冊switch這個子類
->INIT_DELAYED_WORK(&headset->h_delayed_work[HOOK], hook_once_work);
->iio_read_channel_raw(headset_info->chan, &val);
->headset_info->cur_headset_status = headset_info->isMic ? BIT_HEADSET:BIT_HEADSET_NO_MIC;
->switch_set_state(&headset_info->sdev, headset_info->cur_headset_status);//這裏設置耳機的狀態值
->schedule_delayed_work(&headset_info->h_delayed_work[HOOK], msecs_to_jiffies(750));//循環750ms執行一次工作隊列
shell環境下通過執行cat sys/class/switch/h2w/state 查看耳機插入狀態(上層通過獲取這個state值去返回對應的狀態,顯示相應的圖標):
rk3399_all:/ # cat sys/class/switch/h2w/state
state <= 0 表示無耳機插入
state = 1 表示帶 Mic 耳機插入
state = 2 表示不帶 Mic 耳機插入
在system/media/brillo/audio/audioservice/audio_device_handler.cpp獲取狀態更新給上層調用,直接讀取sys/class/switch/h2w/中state值來獲取最新的狀態(以下爲截取的部分代碼)。
static const char kH2WStateFile[] = "/sys/class/switch/h2w/state";
63 void AudioDeviceHandler::GetInitialAudioDeviceState(
64 const base::FilePath& path) {
65 base::File file(path, base::File::FLAG_OPEN | base::File::FLAG_READ);
66 if (!file.IsValid()) {
67 LOG(WARNING) << "Kernel does not have wired headset support. Could not "
68 << "open " << path.value() << "( "
69 << base::File::ErrorToString(file.error_details()) << " ).";
70 return;
71 }
72 int state = 0;
73 int bytes_read = file.ReadAtCurrentPos(reinterpret_cast<char*>(&state), 1);
74 state -= '0';
75 if (bytes_read == 0) {
76 LOG(WARNING) << "Could not read from " << path.value();
77 return;
78 }
79 VLOG(1) << "Initial audio jack state is " << state;
80 static const int kHeadPhoneMask = 0x1;
81 bool headphone = state & kHeadPhoneMask;
82 static const int kMicrophoneMask = 0x2;
83 bool microphone = (state & kMicrophoneMask) >> 1;
84
85 UpdateAudioSystem(headphone, microphone);
86 }