最近在做Marvell的項(xiàng)目，碰到個(gè)耳機(jī)熱插拔的問題，所以順便看了下相關(guān)代碼，這里來貢獻(xiàn)一下給大家。

我們這里以PXA的代碼為例，整個(gè)框架比較的簡(jiǎn)單清晰，上層是分別是HeadsetObserver.java以及HookSwitchObserver.java，

它們會(huì)直接讀取/sys/class/switch/中某一特定的設(shè)備的state，比如"/sys/class/switch/h2w/state"，來獲取最新的狀態(tài)。

我們把它分為兩部分來看

kernel/drivers/switch/

這里存放著headset以及hook的驅(qū)動(dòng)代碼，首先switch_class.c中會(huì)先注冊(cè)switch這個(gè)子類，并提供switch_dev_register這個(gè)注冊(cè)入口，

對(duì)應(yīng)的設(shè)備驅(qū)動(dòng)調(diào)用switch_dev_register把自己注冊(cè)在switch這個(gè)子類中，比如：

switch_data_headset->sdev.name = pdata_headset->name; //name is h2w

switch_data_headset->name_on = pdata_headset->name_on;

switch_data_headset->name_off = pdata_headset->name_off;

switch_data_headset->state_on = pdata_headset->state_on;

switch_data_headset->state_off = pdata_headset->state_off;

switch_data_headset->sdev.print_state = switch_headset_print_state;

info->psw_data_headset = switch_data_headset;

ret = switch_dev_register(&switch_data_headset->sdev);

那么在/sys/class/switch目錄中就會(huì)生成h2w這個(gè)子目錄，里面會(huì)有state,name等一些成員，而驅(qū)動(dòng)判斷耳機(jī)是否插入則是通過

gpio模擬中斷，在耳機(jī)插入的時(shí)候產(chǎn)生電平的變化來調(diào)用中斷回調(diào)函數(shù)，回調(diào)函數(shù)中會(huì)改變state狀態(tài)值，就這么簡(jiǎn)單

frameworks/base/services/java/com/android/server/HeadsetObserver.java這是android耳機(jī)監(jiān)測(cè)的代碼

它會(huì)通過讀取/sys/class/switch/h2w/state來判斷此時(shí)是否有耳機(jī)插入，比如：

private static final String HEADSET_STATE_PATH = "/sys/class/switch/h2w/state";

FileReader file = new FileReader(HEADSET_STATE_PATH);

然后通過

public void onUEvent(UEventObserver.UEvent event) {

if (LOG) Slog.v(TAG, "Headset UEVENT: " + event.toString());

try {

update(event.get("SWITCH_NAME")， Integer.parseInt(event.get("SWITCH_STATE")));

} catch (NumberFormatException e) {

Slog.e(TAG, "Could not parse switch state from event " + event);

}

}

來更新耳機(jī)的檢測(cè)狀態(tài)。hook監(jiān)測(cè)和耳機(jī)監(jiān)測(cè)類似，這里就不再重復(fù)了，寫得有點(diǎn)亂，希望對(duì)朋友們有幫助。