Android2.2源码分析［GPS模块］

内容来源于网络以及自己的一些总结。

GPS JAVA API 示例

下面这个程序在会监听GPS 开启，关闭，位置改变，

public class MainActivity extends Activity implements LocationListener {/** Called when the activity is first created. */private final static String TAG = "LocationTest";TextView tv;Button btn;private LocationManager lm;public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);// 与Location_service建立连接lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);// 注册activity到监听队列中lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1l, 1l, this);}// Location发生变化时会调用这个public void onLocationChanged(Location location) {Log.d(TAG, "location: " + location);}// 关闭GPS卫星会调用这个public void onProviderDisabled(String provider) {Log.d(TAG, "provider disable" + provider);}// 启用GPS卫星会调用这个public void onProviderEnabled(String provider) {Log.d(TAG, "provider enable");}public void onStatusChanged(String provider, int status, Bundle extras) {Log.d(TAG, "status changed status = " + status);}}

 

使用GPS 需要这个权限：

< uses-permission android:name = "android.permission.ACCESS_FINE_LOCATION" >

</ uses-permission >

使用GPS 相关的资源，需要先用getSystemService 获得一个LOCATION_SERVICE 的实例，获得这个实例之后就可以进行相关操作了。

@frameworks/base/services/java/com/android/server/SystemServer.java

LOCATION_SERVICE 是在SystemServer.java 中启动的，也就是系统启动之后，这个服务就已经启动了：

ServiceManager.addService(Context.LOCATION_SERVICE, new LocationManagerService(context));

源码结构

主要分为四部分，client ，service ，jni ，hardware

frameworks/base/location/* (client 部分)

frameworks/base/services/java/com/android/serverLocationManagerService.java （server 部分）

frameworks/base/core/jni/android_location_GpsLocationProvider.cpp （JNI 部分）

hardware/libhardware_legacy/gps/* （hardware 接口部分）

 

1. frameworks/base/location/java (Client 部分)

.

├── android

│   └── location

│   ├── Address.aidl

│   ├── Address.java 描述地理位置信息

│   ├── Criteria.aidl

│   ├── Criteria.java 定位提供商的应用标准

│   ├── Geocoder.java 地理编码，好像是定位信息转换用的

│   ├── GpsSatellite.java 描述当前GPS satellite 信息

│   ├── GpsStatus.java 描述当前GPS engine 信息

│   ├── IGeocodeProvider.aidl

│   ├── IGpsStatusListener.aidl

│   ├── IGpsStatusProvider.aidl

│   ├── ILocationListener.aidl

│   ├── ILocationManager.aidl

│   ├── ILocationProvider.aidl

│   ├── INetInitiatedListener.aidl

│   ├── Location.aidl

│   ├── Location.java 描述定位的详细信息经度，纬度等等

│   ├── LocationListener.java 监听定位服务

│   ├── LocationManager.java 用来访问定位服务AIDL

│   ├── LocationProvider.java 定位提供者信息

│   └── package.html

└── com

└── android

└── internal

└── location

├── DummyLocationProvider.java

├── GpsLocationProvider.java

├── GpsNetInitiatedHandler.java

├── GpsXtraDownloader.java

├── LocationProviderProxy.java

├── MockProvider.java

└── NmeaParser.java

 

2. frameworks/base/services/java/com/android/server/ LocationManagerService.java (server 部分)

 

3. frameworks/base/core/jni/android_location_GpsLocationProvider.cpp (JNI 部分)

 

4. （hardware 接口部分）

hardware/libhardware_legacy/gps.h

hardware/libhardware_legacy/gps_ni.h

hardware/libhardware_legacy/gps/*

.

├── Android.mk

├── gps.cpp

└── gps_qemu.c

代码分析

1. 控制通道，也就是由app 层发起的比如enable 或disable 的控制命令，这个在”设置/ 位置和安全设置/ 使用GPS 卫星”里面设置。

LocationManager.java 主要负责通信。具体的实现在LocationManagerService.java 中，通过AIDL 实现通信，接口文件是ILocationManager.aidl 。在LocationManagerService 在初始化的时候，会判断是否有GPS 设备，如果存在则创建了一个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。

 

2. 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android_location_GpsLocationProvider_wait_for_event()@ anroid_location_GpsLocationProvider.cpp ，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 通过串口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.

 

另外一部分就是hardware/libhardware_legacy/gps 部分的实现，这个主要就是实现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，并且设置callback函数：static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj){ if (!sGpsInterface) sGpsInterface = gps_get_interface(); if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) return false; …...}GpsCallbacks sGpsCallbacks = { location_callback, status_callback, sv_status_callback, nmea_callback};打开串口，注册sGpsCallbacksstatic int qemu_gps_init(GpsCallbacks* callbacks){ GpsState* s = _gps_state; if (!s->init) gps_state_init(s); if (s->fd < 0) return -1; s->callbacks = *callbacks; return 0; } 打开串口，建立Socket连接，创建线程：static void gps_state_init( GpsState* state ) { ... state->fd = qemu_channel_open( &state->channel, QEMU_CHANNEL_NAME, O_RDONLY ); if ( socketpair( AF_LOCAL, SOCK_STREAM, 0, state->control ) < 0 ) { LOGE("could not create thread control socket pair: %s", strerror(errno)); goto Fail; } if ( pthread_create( &state->thread, NULL, gps_state_thread, state ) != 0 ) { LOGE("could not create gps thread: %s", strerror(errno)); goto Fail; } …... } location回调函数：static void location_callback(GpsLocation* location) { pthread_mutex_lock(&sEventMutex); sPendingCallbacks |= kLocation; memcpy(&sGpsLocation, location, sizeof(sGpsLocation)); pthread_cond_signal(&sEventCond); // 线程同步 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); while (sPendingCallbacks == 0) { pthread_cond_wait(&sEventCond, &sEventMutex); } // copy and clear the callback flags int pendingCallbacks = sPendingCallbacks; sPendingCallbacks = 0; int nmeaSentenceCount = mNmeaSentenceCount; mNmeaSentenceCount = 0; // copy everything and unlock the mutex before calling into Java code to avoid the possibility // of timeouts in the GPS engine. if (pendingCallbacks & kLocation) memcpy(&sGpsLocationCopy, &sGpsLocation, sizeof(sGpsLocationCopy)); if (pendingCallbacks & kStatus) memcpy(&sGpsStatusCopy, &sGpsStatus, sizeof(sGpsStatusCopy)); if (pendingCallbacks & kSvStatus) memcpy(&sGpsSvStatusCopy, &sGpsSvStatus, sizeof(sGpsSvStatusCopy)); if (pendingCallbacks & kAGpsStatus) memcpy(&sAGpsStatusCopy, &sAGpsStatus, sizeof(sAGpsStatusCopy)); if (pendingCallbacks & kNmeaAvailable) memcpy(&sNmeaBufferCopy, &sNmeaBuffer, nmeaSentenceCount * sizeof(sNmeaBuffer[0])); if (pendingCallbacks & kNiNotification) memcpy(&sGpsNiNotificationCopy, &sGpsNiNotification, sizeof(sGpsNiNotificationCopy)); 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 & kAGpsStatus) { env->CallVoidMethod(obj, method_reportAGpsStatus, sAGpsStatusCopy.type, sAGpsStatusCopy.status); } if (pendingCallbacks & kNmeaAvailable) { for (int i = 0; i < nmeaSentenceCount; i++) { env->CallVoidMethod(obj, method_reportNmea, i, sNmeaBuffer[i].timestamp); } } 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. } if (pendingCallbacks & kNiNotification) { LOGD("android_location_GpsLocationProvider_wait_for_event: sent notification callback."); jstring reqId = env->NewStringUTF(sGpsNiNotificationCopy.requestor_id); jstring text = env->NewStringUTF(sGpsNiNotificationCopy.text); jstring extras = env->NewStringUTF(sGpsNiNotificationCopy.extras); env->CallVoidMethod(obj, method_reportNiNotification, sGpsNiNotificationCopy.notification_id, sGpsNiNotificationCopy.ni_type, sGpsNiNotificationCopy.notify_flags, sGpsNiNotificationCopy.timeout, sGpsNiNotificationCopy.default_response, reqId, text, sGpsNiNotificationCopy.requestor_id_encoding, sGpsNiNotificationCopy.text_encoding, extras ); }}

 

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。

 

 

从Framework 到HAL 调用过程大致如下：

android_location_GpsLocationProvider_init gps_get_interface 获取GPS接口gps_find_hardware来获取硬件设备信息，根据宏定义来判断#ifdef HAVE_QEMU_GPS_HARDWAREsGpsInterface = gps_get_qemu_interface() 源码中只有对qemu的实现，#ifdef HAVE_GPS_HARDWARE sGpsInterface = gps_get_hardware_interface();这部分是需要自己根据硬件情况来实现gps_get_qemu_interfaceqemu_gps_init(GpsCallbacks* callbacks)gps_state_init( GpsState* state )qemu_channel_open打开GPS串口设备socketpair创建SOCKET用来控制下面的Threadpthread_create(…, gps_state_thread, …)gps_state_thread( void* arg )epoll_createnmea_reader_init( reader );epoll_register( epoll_fd, control_fd ); epoll_register( epoll_fd, gps_fd );for (;;) {//创建循环不停的扫描串口 nevents = epoll_wait( epoll_fd, events, 2, -1 );if (fd == control_fd){ret = read( fd, &cmd, 1 );nmea_reader_set_callback}if (fd == gps_fd) {for (;;) { int nn, ret; ret = read( fd, buff, sizeof(buff) ); for (nn = 0; nn < ret; nn++) nmea_reader_addc( reader, buff[nn] );}nmea_reader_addc( NmeaReader* r, int c )nmea_reader_parse( NmeaReader* r )nmea_tokenizer_initnmea_tokenizer_getGGA数据处理nmea_reader_update_time// 更新时间nmea_reader_update_latlong// 更新经度，纬度nmea_reader_update_altitude// 更新高度RMC数据处理nmea_reader_update_datenmea_reader_update_latlongnmea_reader_update_bearingnmea_reader_update_speedr->callback( &r->fix );// 解析后的数据上报

 

Android 2.2 Settings 程序GPS 设置：

在Settings -> Location & security ->My Location 里面有”Use wireless networks” 和”Use GPS satelites” 两个选项。一个是通过网络定位（Internet/Mobile networks ），另一个是通过GPS 芯片定位。

 

这部分相应的代码：

packages/apps/Settings/src/com/android/settings/SecuritySettings.java

 

SecuritySettings.java 中的大概调用流程如下：

首先加载XML 绑定视图：

onCreate()

createPreferenceHierarchy()

addPreferencesFromResource(R.xml.security_settings);

mGps = (CheckBoxPreference) getPreferenceScreen().findPreference(LOCATION_GPS);

mAssistedGps = (CheckBoxPreference) getPreferenceScreen().findPreference(ASSISTED_GPS);

 

然后onPreferenceTreeClick 方法会监听check ，uncheck 事件。

如果Use GPS satelites 被选择，就会调用：

＠/frameworks/base/core/java/android/provider/Settings.java

Settings.Secure.setLocationProviderEnabled(getContentResolver(),

LocationManager.GPS_PROVIDER , enabled);

putString(cr, Settings.Secure.LOCATION_PROVIDERS_ALLOWED, provider);

putString(ContentResolver resolver, Uri uri, String name, String value)

values.put(NAME, name); // name = location_providers_allowed

values.put(VALUE, value);

resolver.insert(uri, values);

最后会调用resolver.insert(uri, values); 把写到数据库（uri=”content://settings/secure” ）中。

 

如果Use wireless networks 被选中：

Settings.Secure.setLocationProviderEnabled(getContentResolver(),

LocationManager.NETWORK_PROVIDER , mNetwork.isChecked());

后续的调用都是一样的，只是参数不同。

Google Android 2.2 AGPS 说明：

谷歌在security_settings.xml 文件中注释掉了AGPS 的部分，解释如下：

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"> <PreferenceCategory android:key="location_category" android:title="@string/location_title"> <CheckBoxPreference android:key="location_network" android:title="@string/location_network_based" android:summaryOn="@string/location_neighborhood_level" android:summaryOff="@string/location_networks_disabled"/> <CheckBoxPreference android:key="location_gps" android:title="@string/location_gps" android:summaryOn="@string/location_street_level" android:summaryOff="@string/location_gps_disabled"/><!-- Disabled to avoid confusion on devices with no AGPS For Google experience devices we want AGPS on by default (if supported) so we don't really need this. <CheckBoxPreference android:key="assisted_gps" android:title="@string/assisted_gps" android:summaryOn="@string/assisted_gps_enabled" android:summaryOff="@string/assisted_gps_disabled"/>--> </PreferenceCategory></PreferenceScreen>