轉自:http://embed.chinaitlab.com/J2ME/877029.html
最近在做Marvell的項目,碰到個耳機熱插拔的問題,所以順便看了下相關代碼,這裡來貢獻一下給大家。
我們這裡以PXA的代碼為例,整個架構比較的簡單清晰,上層是分別是HeadsetObserver.java以及HookSwitchObserver.java,
它們會直接讀取/sys/class/switch/中某一特定的裝置的state,比如"/sys/class/switch/h2w/state",來擷取最新的狀態。
我們把它分為兩部分來看
kernel/drivers/switch/
這裡存放著headset以及hook的驅動代碼,首先switch_class.c中會先註冊switch這個子類,並提供switch_dev_register這個註冊入口,
對應的裝置驅動調用switch_dev_register把自己註冊在switch這個子類中,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);
那麼在/sys/class/switch目錄中就會產生h2w這個子目錄,裡面會有state,name等一些成員,而驅動判斷耳機是否插入則是通過
gpio類比中斷,在耳機插入的時候產生電平的變化來調用中斷回呼函數,回呼函數中會改變state狀態值,就這麼簡單
frameworks/base/services/java/com/android/server/HeadsetObserver.java這是android耳機監測的代碼
它會通過讀取/sys/class/switch/h2w/state來判斷此時是否有耳機插入,比如:
private static final String HEADSET_STATE_PATH = "/sys/class/switch/h2w/state";
FileReader file = new FileReader(HEADSET_STATE_PATH);
然後通過
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);
}
}
來更新耳機的檢測狀態。hook監測和耳機監測類似,這裡就不再重複了,寫得有點亂,希望對朋友們有協助。