GPS 研究一 （Android2.3）

（红字表示2.3的变化）

Framework：

1.frameworks/base/location/java/android/location
这里主要是用来被App调用的，API包是android.location。

2.frameworks/base/location/java/com/android/internal/location
这个目录是Framework对Location服务的内部实现。

3.framework/services/java/com/android/server
这个目录只有一个文件

|-- LocationManagerService.java
是Location服务对内部实现的一种封装。

JNI：

2.2
frameworks/base/core/jni/android_location_GpsLocationProvider.cpp

2.3

/framework/base/services/jni/com_android_server_location_GpsLocationProvider.cpp

JNI层只有一个文件，起到承上启下的作用。上层承接Framework，下层调用HAL层具体硬件抽象实现。

HAL：Hardware Abstract Layer 硬件抽象层
hardware/libhardware_legacy/gps
hardware/libhardware_legacy/include/hardware_legacy/gps.h
HAL层相当于一个linux应用程序接口，通过open，close等操作，操作硬件设备。Android的源代码只实现了模拟器的gps接口，具体在文件gps_qemu.c中。在2.2版本中提供了对QCOM公司的gps的实现，在以下目录：
/hardware/qcom

下面介绍几个重要的数据结构：

1. GpsInterface接口是gps模块中最重要的数据结构，它是底层驱动实现的接口，如果要porting到自己的板子上，就需要实现这些接口。该接口的定义在gps.h中，模拟器实现在gps_qemu.c中。

/** Represents the standard GPS interface. */typedef struct { /** set to sizeof(GpsInterface) */ size_t size; /** * Opens the interface and provides the callback routines * to the implemenation of this interface. */ int (*init)( GpsCallbacks* callbacks ); /** Starts navigating. */ int (*start)( void ); /** Stops navigating. */ int (*stop)( void ); /** Closes the interface. */ void (*cleanup)( void ); /** Injects the current time. */ int (*inject_time)(GpsUtcTime time, int64_t timeReference, int uncertainty); /** Injects current location from another location provider * (typically cell ID). * latitude and longitude are measured in degrees * expected accuracy is measured in meters */ int (*inject_location)(double latitude, double longitude, float accuracy); /** * Specifies that the next call to start will not use the * information defined in the flags. GPS_DELETE_ALL is passed for * a cold start. */ void (*delete_aiding_data)(GpsAidingData flags); /** * min_interval represents the time between fixes in milliseconds. * preferred_accuracy represents the requested fix accuracy in meters. * preferred_time represents the requested time to first fix in milliseconds. */ int (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence, uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time); /** Get a pointer to extension information. */ const void* (*get_extension)(const char* name);} GpsInterface;

2.GpsCallbacks回调函数

这个是回调函数结构体，定义也在gps.h中。它们的实现是在com_android_server_android_location_GpsLocationProvider.cpp中，google已经实现了，我们不需要做任何动作。

2.2

/** GPS callback structure. */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;} GpsCallbacks;

2.3 中 多加入了 以下几个回调函数

gps_set_capabilities set_capabilities_cb; gps_acquire_wakelock acquire_wakelock_cb; gps_release_wakelock release_wakelock_cb; gps_create_thread create_thread_cb;

 

3. GpsLocation

表示Locatin数据信息，底层驱动获得Location的raw信息，通常是nmea码，然后通过解析就得到了location信息。

其中Android2.3比android2.2多加入了 size 属性 以获取其大小。

/** Represents a location. */typedef struct { /** set to sizeof(GpsLocation) */ size_t size; /** Contains GpsLocationFlags bits. */ uint16_t flags; /** Represents latitude in degrees. */ double latitude; /** Represents longitude in degrees. */ double longitude; /** Represents altitude in meters above the WGS 84 reference * ellipsoid. */ double altitude; /** Represents speed in meters per second. */ float speed; /** Represents heading in degrees. */ float bearing; /** Represents expected accuracy in meters. */ float accuracy; /** Timestamp for the location fix. */ GpsUtcTime timestamp;} GpsLocation;