几个主要的文件及目录：
frameworks/base/location/* (client部分)
frameworks/base/core/jni/android_location_GpsLocationProvider.cpp （JNI 部分）
frameworks/base/services/java/com/android/serverLocationManagerService.java（server 部分）
hardware/libhardware_legacy/gps/* （hardware 接口部分）
一是：控制通道，也就是由app层发起的比如enable或disable的控制命令。
example代码调用LocationManager.java ，再通过IPC来实现真正的调用。LocationManager.java 主要负责通信。具体的实现在LocationManagerService.java中。
接口文件是ILocationManager.aidl。在service中根据provider来创建了一个GpsLocationProvider.java，并通过JNI调 android_location_GpsLocationProvider.cpp，该文件再通过GPSInterface来调用硬件的具体实现代码。
二是： enable后的Location数据和状态上报。对于数据的上报过程，主要就是关注几个callback函数。主要代码分析如下：
在 GpsLocationProvider.java文件中enable()一个GpsLocationProvider时，会启动一个 GpsEventThread,该线程主要就是调用了native_wait_for_event();通过JNI调用到了 anroid_location_GpsLocationProvider.cpp中的 android_location_GpsLocationProvider_wait_for_event();而该event的触发是由来自硬件驱动 Location数据包的上报，底层的硬件驱动程序会把raw gps data通过pipe或其他的方式，送出来，这个要看gps驱动的实现了，我们通过自己实现的GpsInterface 来解析raw gps data并调用loaction_callback()来触发event并copy Location数据，等待到event后再调用GpsLocationProvider.java中的reportLocation()上报Location.
除了框架代码外，我们自己需要实现的代码也分为两块，一个是app层的代码，app层我也提供一个简单的代码例子，请参考以下代码:
public class LocationSample extends Activity implements LocationListener {
private LocationManager lm;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
lm.requestLocationUpdates(LocationManager.GPS_PROVIDER,1l,1l,this);
}
public void onLocationChanged(Location location) {
// TODO Auto-generated method stub
Log.d(TAG,"location: ");
}
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
Log.d(TAG,"provider disable");
}
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
Log.d(TAG,"provider enable");
}
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
Log.d(TAG,"status changed");
}
}
另外一部分就是hardware/libhardware_legacy/gps 部分的实现，这个主要就是实现一个gps.h里面的几个数据结构：
typedef struct {
gps_location_callback location_cb;
gps_status_callback status_cb;
gps_sv_status_callback sv_status_cb;
} GpsCallbacks;
typedef struct {
int (*init)( GpsCallbacks* callbacks );
int (*start)( void );
int (*stop)( void );
void (*set_fix_frequency)( int frequency );
void (*cleanup)( void );
int (*inject_time)(GpsUtcTime time, int64_t timeReference,
int uncertainty);
void (*delete_aiding_data)(GpsAidingData flags);
int (*set_position_mode)(GpsPositionMode mode, int fix_frequency);
const void* (*get_extension)(const char* name);
} GpsInterface;
typedef struct {
uint16_t flags;
double latitude;
double longitude;
double altitude;
float speed;
float bearing;
float accuracy;
GpsUtcTime timestamp;
} GpsLocation;
在GpsInterface->init()的时候要把上层的GpsCallbacks传进来，然后start后，从驱动那里poll获得gps raw data，并对raw data进行解析并填充GpsLocation数据结构，然后调用location_cb 上报location 数据。
//初始化的时候，得到GpsInterface，调用init,
static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj)
{
if (!sGpsInterface)
sGpsInterface = gps_get_interface();
return (sGpsInterface && sGpsInterface->init(&sGpsCallbacks) == 0);
}
GpsCallbacks sGpsCallbacks = {
location_callback,
status_callback,
sv_status_callback,
};
//并且打开串口，注册sGpsCallbacks
qemu_gps_init(GpsCallbacks* callbacks)
----> GpsState* s = _gps_state;
----> gps_state_init(s);
----> s->callbacks = *callbacks;
//打开串口，创建线程
gps_state_init( GpsState* state )
-----> state->fd = qemu_channel_open_gps
-----> pthread_create( &state->thread, NULL, gps_state_thread, state )
static void location_callback(GpsLocation* location)
{
pthread_mutex_lock(&sEventMutex);
sPendingCallbacks |= kLocation;
memcpy(&sGpsLocation, location, sizeof(sGpsLocation));
pthread_cond_signal(&sEventCond); //同步西面的函数
pthread_mutex_unlock(&sEventMutex);
}
//下面这个函数就是由上层的 java调用的，并且等待底层的硬件发送数据，其中由EventCond同步
static void android_location_GpsLocationProvider_wait_for_event(JNIEnv* env, jobject obj)
{
pthread_mutex_lock(&sEventMutex);
pthread_cond_wait(&sEventCond, &sEventMutex);
// copy and clear the callback flags
int pendingCallbacks = sPendingCallbacks;
sPendingCallbacks = 0;
// copy everything and unlock the mutex before calling into Java code to avoid the possibility
// of timeouts in the GPS engine.
memcpy(&sGpsLocationCopy, &sGpsLocation, sizeof(sGpsLocationCopy));
memcpy(&sGpsStatusCopy, &sGpsStatus, sizeof(sGpsStatusCopy));
memcpy(&sGpsSvStatusCopy, &sGpsSvStatus, sizeof(sGpsSvStatusCopy));
pthread_mutex_unlock(&sEventMutex);
if (pendingCallbacks & kLocation) {
env->CallVoidMethod(obj, method_reportLocation, sGpsLocationCopy.flags,
(jdouble)sGpsLocationCopy.latitude, (jdouble)sGpsLocationCopy.longitude,
(jdouble)sGpsLocationCopy.altitude,
(jfloat)sGpsLocationCopy.speed, (jfloat)sGpsLocationCopy.bearing,
(jfloat)sGpsLocationCopy.accuracy, (jlong)sGpsLocationCopy.timestamp);
}
if (pendingCallbacks & kStatus) {
env->CallVoidMethod(obj, method_reportStatus, sGpsStatusCopy.status);
}
if (pendingCallbacks & kSvStatus) {
env->CallVoidMethod(obj, method_reportSvStatus);
}
if (pendingCallbacks & kXtraDownloadRequest) {
env->CallVoidMethod(obj, method_xtraDownloadRequest);
}
if (pendingCallbacks & kDisableRequest) {
// don't need to do anything - we are just poking so wait_for_event will return.
}
}
//hardware 那部分有个线程gps_state_thread 一直在读串口的内容并进行解析，最后解析到location的信息
由cpp文件的GpsCallbacks sGpsCallbacks = { location_callback....}同步上层的线程
gps_state_thread
----->nmea_reader_addc
----->nmea_reader_parse
------> location_callback
------->数据上报 |
发表于 2012-2-23 11:26:39