Android GPS架构分析-preview

Android GPS架构分析

Daniel Wood 20101222

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文章出处：http://danielwood.cublog.cn

作者：Daniel Wood

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看Android的GPS模块有两个月了吧，终于可以写点东西出来。首先来看看GPS模块的代码结构：

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：
frameworks/base/core/jni/android_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 {     /**      * 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) ;     /**      * fix_frequency represents the time between fixes in seconds.      * Set fix_frequency to zero for a single-shot fix.      */     int ( * set_position_mode) ( GpsPositionMode mode, int fix_frequency) ;     /** 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 android_location_GpsLocationProvider.cpp 中，google已经实现了，我们不需要做任何动作。

 

/** GPS callback structure. */ typedef struct {         gps_location_callback location_cb;         gps_status_callback status_cb;         gps_sv_status_callback sv_status_cb;         gps_nmea_callback nmea_cb; } GpsCallbacks; /** Callback with location information. */ typedef void ( * gps_location_callback) ( GpsLocation* location) ; /** Callback with status information. */ typedef void ( * gps_status_callback) ( GpsStatus* status) ; /** Callback with SV status information. */ typedef void ( * gps_sv_status_callback) ( GpsSvStatus* sv_info) ; /** Callback for reporting NMEA sentences. */ typedef void ( * gps_nmea_callback) ( GpsUtcTime timestamp, const char * nmea, int length) ;

 

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。

/** Represents a location. */ typedef struct {     /** 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;