android gps机制分析--之三
1 gps打开/初始化
在Java层打开gps,其实对于gps库来说,就是执行初始化过程。
1.1 Java层分析
android系统中打开GPS的方法往数据库里面写值,
private void enableGps(boolean enable) {
try {
Settings.Secure.setLocationProviderEnabled(getContentResolver(),
LocationManager.GPS_PROVIDER, enable);
} catch (Exception e) {
}
}
最后往setting数据库中的location_providers_allowed字段写值。
putStringForUser(cr, Settings.Secure.LOCATION_PROVIDERS_ALLOWED, provider, userId);LocationManagerService的systemRunning方法中会监听setting数据库中的location_providers_allowed字段值的变化,
mContext.getContentResolver().registerContentObserver(
Settings.Secure.getUriFor(Settings.Secure.LOCATION_PROVIDERS_ALLOWED), true,
new ContentObserver(mLocationHandler) {
@Override
public void onChange(boolean selfChange) {
synchronized (mLock) {
updateProvidersLocked();
}
}
}, UserHandle.USER_ALL);
如果该值有变化,则调用updateProvidersLocked方法。主要的流程图如下,
在updateProvidersLocked方法中,如果支持gps,调用updateProviderListenersLocked方法,
updateProviderListenersLocked(name, true);updateProviderListenersLocked主要方法如下,
•••••
boolean shouldBeEnabled = isAllowedByCurrentUserSettingsLocked(name);
••••
if (enabled) {
p.enable();
if (listeners > 0) {
applyRequirementsLocked(provider);
}
} else {
p.disable();
}
首先调用isAllowedByCurrentUserSettingsLocked方法读取数据库字段值,然后根据该值进行相应的打开/关闭GPS操作。
private boolean isAllowedByCurrentUserSettingsLocked(String provider) {
if (mEnabledProviders.contains(provider)) {
return true;
}
if (mDisabledProviders.contains(provider)) {
return false;
}
// Use system settings
ContentResolver resolver = mContext.getContentResolver();
return Settings.Secure.isLocationProviderEnabledForUser(resolver, provider, mCurrentUserId);
}
Settings中的isLocationProviderEnabledForUser方法如下,
public static final boolean isLocationProviderEnabledForUser(ContentResolver cr, String provider, int userId) {
String allowedProviders = Settings.Secure.getStringForUser(cr,
LOCATION_PROVIDERS_ALLOWED, userId);
return TextUtils.delimitedStringContains(allowedProviders, ',', provider);
}
GpsLocationProvider的enable方法如下,
@Override
public void enable() {
synchronized (mLock) {
if (mEnabled) return;
mEnabled = true;
}
sendMessage(ENABLE, 1, null);
}
ProviderHandler对ENABLE消息处理如下,
case ENABLE:
if (msg.arg1 == 1) {
handleEnable();
} else {
handleDisable();
}
break;
handleEnable方法如下,
private void handleEnable() {
if (DEBUG) Log.d(TAG, "handleEnable");
boolean enabled = native_init(); //初始化GPS HAL层模块
if (enabled) {
mSupportsXtra = native_supports_xtra();//判断GPS模块是否支持Xtra
// TODO: remove the following native calls if we can make sure they are redundant.
if (mSuplServerHost != null) {// 设置SUPL服务器地址和端口
native_set_agps_server(AGPS_TYPE_SUPL, mSuplServerHost, mSuplServerPort);
}
if (mC2KServerHost != null) { //设置CDMA2000
native_set_agps_server(AGPS_TYPE_C2K, mC2KServerHost, mC2KServerPort);
}
mGpsMeasurementsProvider.onGpsEnabledChanged();
mGpsNavigationMessageProvider.onGpsEnabledChanged();
} else {
synchronized (mLock) {
mEnabled = false;
}
Log.w(TAG, "Failed to enable location provider");
}
}
1.2 HAL初始化
com_android_server_location_GpsLocationProvider的android_location_GpsLocationProvider_init方法如下,
static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj)
{
// this must be set before calling into the HAL library
if (!mCallbacksObj)
mCallbacksObj = env->NewGlobalRef(obj);
// fail if the main interface fails to initialize
if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0)
return JNI_FALSE;
// if XTRA initialization fails we will disable it by sGpsXtraInterface to NULL,
// but continue to allow the rest of the GPS interface to work.
if (sGpsXtraInterface && sGpsXtraInterface->init(&sGpsXtraCallbacks) != 0)
sGpsXtraInterface = NULL;
if (sAGpsInterface)
sAGpsInterface->init(&sAGpsCallbacks);
if (sGpsNiInterface)
sGpsNiInterface->init(&sGpsNiCallbacks);
if (sAGpsRilInterface)
sAGpsRilInterface->init(&sAGpsRilCallbacks);
if (sGpsGeofencingInterface)
sGpsGeofencingInterface->init(&sGpsGeofenceCallbacks);
return JNI_TRUE;
}
主要是向HAL层设置回调方法接口,当HAL层有情况需要通知JNI层时,就会回调这些方法。
这6组回调方法的定义,回调方法几乎完全一样。sGpsCallbacks的定义如下,
GpsCallbacks sGpsCallbacks = {
sizeof(GpsCallbacks),
location_callback,
status_callback,
sv_status_callback,
nmea_callback,
set_capabilities_callback,
acquire_wakelock_callback,
release_wakelock_callback,
create_thread_callback,
request_utc_time_callback,
};
sGpsCallbacks中包含9个回调方法。
这样,HAL库就可以回调C方法了。
由此可见, com_android_server_location_GpsLocationProvider只是Java和HAL库之间的一个纽带。
1,Java中加载HAL库,并且对HAL库进行初始化。然后就可以对HAL的GPS发出指令,例如打开,关闭GPS等。这时数据流的方向为,
Java-->JNI--> GPS库
2,GPS库中执行打开/关闭动作,向Java上报卫星以及定位消息。这时数据流的方向为,
GPS库-->JNI--> Java
GPS库中对应的init方法为, loc.cpp 的loc_init方法,
static int loc_init(GpsCallbacks* callbacks)
{
int retVal = -1;
ENTRY_LOG();
LOC_API_ADAPTER_EVENT_MASK_T event;
if (NULL == callbacks) {
LOC_LOGE("loc_init failed. cb = NULL\n");
EXIT_LOG(%d, retVal);
return retVal;
}
event = LOC_API_ADAPTER_BIT_PARSED_POSITION_REPORT |
LOC_API_ADAPTER_BIT_SATELLITE_REPORT |
LOC_API_ADAPTER_BIT_LOCATION_SERVER_REQUEST |
LOC_API_ADAPTER_BIT_ASSISTANCE_DATA_REQUEST |
LOC_API_ADAPTER_BIT_IOCTL_REPORT |
LOC_API_ADAPTER_BIT_STATUS_REPORT |
LOC_API_ADAPTER_BIT_NMEA_1HZ_REPORT |
LOC_API_ADAPTER_BIT_NI_NOTIFY_VERIFY_REQUEST;
// 继续注册回调
LocCallbacks clientCallbacks = {local_loc_cb, /* location_cb */
callbacks->status_cb, /* status_cb */
local_sv_cb, /* sv_status_cb */
callbacks->nmea_cb, /* nmea_cb */
callbacks->set_capabilities_cb, /* set_capabilities_cb */
callbacks->acquire_wakelock_cb, /* acquire_wakelock_cb */
callbacks->release_wakelock_cb, /* release_wakelock_cb */
callbacks->create_thread_cb, /* create_thread_cb */
NULL, /* location_ext_parser */
NULL, /* sv_ext_parser */
callbacks->request_utc_time_cb, /* request_utc_time_cb */
};
gps_loc_cb = callbacks->location_cb;
gps_sv_cb = callbacks->sv_status_cb;
// loc_eng_init以及里面的方法较复杂,暂不论述。
retVal = loc_eng_init(loc_afw_data, &clientCallbacks, event, NULL);
loc_afw_data.adapter->mSupportsAgpsRequests = !loc_afw_data.adapter->hasAgpsExtendedCapabilities();
loc_afw_data.adapter->mSupportsPositionInjection = !loc_afw_data.adapter->hasCPIExtendedCapabilities();
loc_afw_data.adapter->mSupportsTimeInjection = !loc_afw_data.adapter->hasCPIExtendedCapabilities();
loc_afw_data.adapter->setGpsLockMsg(0);
loc_afw_data.adapter->requestUlp(getCarrierCapabilities());
loc_afw_data.adapter->setXtraUserAgent();
if(retVal) {
LOC_LOGE("loc_eng_init() fail!");
goto err;
}
loc_afw_data.adapter->setPowerVoteRight(loc_get_target() == TARGET_QCA1530);
loc_afw_data.adapter->setPowerVote(true);
LOC_LOGD("loc_eng_init() success!");
err:
EXIT_LOG(%d, retVal);
return retVal;
}
gps.h中有对应的GpsCallbacks结构,
typedef struct {
/** set to sizeof(GpsCallbacks) */
size_t size;
gps_location_callback location_cb;
gps_status_callback status_cb;
gps_sv_status_callback sv_status_cb;
gps_nmea_callback nmea_cb;
gps_set_capabilities set_capabilities_cb;
gps_acquire_wakelock acquire_wakelock_cb;
gps_release_wakelock release_wakelock_cb;
gps_create_thread create_thread_cb;
gps_request_utc_time request_utc_time_cb;
} GpsCallbacks;
这样,HAL层的gps_location_callback方法就对应com_android_server_location_GpsLocationProvide
中的location_callback方法,其他的回调对应的也一样。