基于Android 的GPS 移植

最近负责 Android 驱动的GPS部分，所谓Android驱动我觉得可以说成是linux应用

之前发了一个图描述了 Android GPS 架构

基于Android 的GPS 移植

GPS芯片大多采用串口通信，所以只要CPU能够提供一个UART 驱动，那么跟GPS芯片通信是没有问题的，

但是现在很多GPS功能不是一个单独的芯片，大部分都是一个芯片上有好几种无线模块比如 Blletooth WiFi FM等

有时候有些功能就会去复用一个UART，这样在管理上就相对麻烦，要将一个UART驱动，模拟成一个HCI的接口而后才能使GPS功能（TI1281）

比较好的是我们的项目是单一的GPS chip 听说apple也是用的这一款,不过人家拿的是全部的source code，而我们只有部分的code而没有核心算法的code 很郁闷，但是即便是只有部分code从里边还是可以学到很多的机制

对于android GPS驱动来说主要的工作是实现HAL层计编译生成一个叫做gps.***.so的动态库的代码.
由app发出定位申请，此时会去启动一个定位服务线程，此线程会调用到Location provider 服务在App Framwork中，在次会通过被native方法调用到JNI中，JNI获得GpsInterface并传给接口一个回调函数的实现。
GpsInterface就是由HAL层最主要实现

介绍下gps.h下得重要相关结构题定义
在android2.3中gps.h定义在/hardware/inclue/hardware下
主要的结构
1、相关宏定义：

定位模式定义
/** Requested operational mode for GPS operation. */
typedef uint32_t GpsPositionMode;
// IMPORTANT: Note that the following values must match
// constants in GpsLocationProvider.java.
/** Mode for running GPS standalone (no assistance). */
#define GPS_POSITION_MODE_STANDALONE    0    //纯GPS 使用卫星定位
/** AGPS MS-Based mode. */
#define GPS_POSITION_MODE_MS_BASED      1    //基于用户终端的A-GPS
/** AGPS MS-Assisted mode. */
#define GPS_POSITION_MODE_MS_ASSISTED   2    //基于用户终端辅助A-GPS
工作模式
/** Requested recurrence mode for GPS operation. */
typedef uint32_t GpsPositionRecurrence;
// IMPORTANT: Note that the following values must match
// constants in GpsLocationProvider.java.
/** Receive GPS fixes on a recurring basis at a specified period. */
#define GPS_POSITION_RECURRENCE_PERIODIC 0//周期性的
/** Request a single shot GPS fix. */
#define GPS_POSITION_RECURRENCE_SINGLE 1//单次工作
辅助数据（在测试GPS性能时候又是需要删除全部或部分的辅助数据）
/** Flags used to specify which aiding data to delete
    when calling delete_aiding_data(). */
typedef uint16_t GpsAidingData;
// IMPORTANT: Note that the following values must match
// constants in GpsLocationProvider.java.
#define GPS_DELETE_EPHEMERIS        0x0001
#define GPS_DELETE_ALMANAC          0x0002
#define GPS_DELETE_POSITION         0x0004
#define GPS_DELETE_TIME             0x0008
#define GPS_DELETE_IONO             0x0010
#define GPS_DELETE_UTC              0x0020
#define GPS_DELETE_HEALTH           0x0040
#define GPS_DELETE_SVDIR            0x0080
#define GPS_DELETE_SVSTEER          0x0100
#define GPS_DELETE_SADATA           0x0200
#define GPS_DELETE_RTI              0x0400
#define GPS_DELETE_CELLDB_INFO      0x8000
#define GPS_DELETE_ALL              0xFFFF
gps芯片可以处理的“能力”
/** Flags for the gps_set_capabilities callback. */

/** GPS HAL schedules fixes for GPS_POSITION_RECURRENCE_PERIODIC mode.
    If this is not set, then the framework will use 1000ms for min_interval
    and will start and call start() and stop() to schedule the GPS.
*/
#define GPS_CAPABILITY_SCHEDULING       0x0000001/** GPS supports MS-Based AGPS mode */
#define GPS_CAPABILITY_MSB              0x0000002/** GPS supports MS-Assisted AGPS mode */
#define GPS_CAPABILITY_MSA              0x0000004/** GPS supports single-shot fixes */
#define GPS_CAPABILITY_SINGLE_SHOT      0x0000008
还有很多的定义此处不一一列举在gps.h中都有很好的解释。

2、数据结构体

GpsLocation
定义了一个表示方位的结构体，成员有经纬度，高度，速度，方位角等。
GpsStatus
表示GPS的当前状态，只有两个成员一个是表示结构大小的成员，与一个表示Gps状态的类型GpsStatusValue
/** GPS status event values. */
typedef uint16_t GpsStatusValue;
// IMPORTANT: Note that the following values must match
// constants in GpsLocationProvider.java.
/** GPS status unknown. */
#define GPS_STATUS_NONE             0/** GPS has begun navigating. */
#define GPS_STATUS_SESSION_BEGIN    1/** GPS has stopped navigating. */
#define GPS_STATUS_SESSION_END      2/** GPS has powered on but is not navigating. */
#define GPS_STATUS_ENGINE_ON        3/** GPS is powered off. */
#define GPS_STATUS_ENGINE_OFF       4
GpsSvInfo
表示当前的卫星信息，有卫星编号，信号强度，卫星仰望角方位角等
GpsSvStatus
表示卫星状态，包含了GpsSvInfo结构，可见卫星数，星历时间，年历时间，与用来定位的卫星的卫星构成的一个掩码
AGpsRefLocation
/* 2G and 3G */
/* In 3G lac is discarded */
typedef struct {
    uint16_t type;
    uint16_t mcc;
    uint16_t mnc;
    uint16_t lac;
    uint32_t cid;
} AGpsRefLocationCellID;

typedef struct {
    uint8_t mac[6];
} AGpsRefLocationMac;

/** Represents ref locations */
typedef struct {
    uint16_t type;
    union {
        AGpsRefLocationCellID   cellID;
        AGpsRefLocationMac      mac;
    } u;
} AGpsRefLocation;
/** Represents the status of AGPS. */
typedef struct {
    /** set to sizeof(AGpsStatus) */
    size_t          size;

    AGpsType        type;
    AGpsStatusValue status;
} AGpsStatus

3、回调函数指针定义

/* Callback with location information. 告知上层位置信息*/
typedef void (* gps_location_callback)(GpsLocation* location);

/** Callback with status information.GPS状态信息回调*/
typedef void (* gps_status_callback)(GpsStatus* status);

/** Callback with SV status information.卫星状态信息回调 */
typedef void (* gps_sv_status_callback)(GpsSvStatus* sv_info);

/** Callback for reporting NMEA sentences. 向上层传递NEMA数据*/
typedef void (* gps_nmea_callback)(GpsUtcTime timestamp, const char* nmea, int length);

/** Callback to inform framework of the GPS engine's capabilities.告知上层次GPS能实现那些功能 */
typedef void (* gps_set_capabilities)(uint32_t capabilities);

/** Callback utility for acquiring the GPS wakelock.gps上锁让gps功能不会被suspend*/
typedef void (* gps_acquire_wakelock)();

/** Callback utility for releasing the GPS wakelock. 释放锁*/
typedef void (* gps_release_wakelock)();

/** Callback for creating a thread that can call into the Java framework code.thread create
在次线程处理函数中通常会由一个无限的循环，去等待上层的请求，并应答*/
typedef pthread_t (* gps_create_thread)(const char* name, void (*start)(void *), void* arg);

4、接口结构体

GpsCallbacks
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;
} GpsCallbacks；

就是以上函数指针组成的结构体，是一组回调函数，函数的实现在JNI层是Android实现好了得，无需做（太大的）修改
GpsInterface
Android GPS 最主要的数据结构，我们最主要的移植工作就是实现其中的函数
/** Represents the standard GPS interface. */
typedef struct {
    /** set to sizeof(GpsInterface) */
    size_t          size;
    /*Opens the interface and provides the callback routines 初始化callbacks 为JNI传下来的
   在此会使用callbacks中的create_thread_cb 来创建一个线程处理函数一直循环，等待任务处理*/
    int   (*init)( GpsCallbacks* callbacks );

    /** Starts navigating. */
    int   (*start)( void );

    /** Stops navigating. */
    int   (*stop)( void );

    /** Closes the interface. */
    void  (*cleanup)( void );

    /** Injects the current time. 填入时间*/
    int   (*inject_time)(GpsUtcTime time, int64_t timeReference,
                         int uncertainty);

    /** Injects current location from another location provider 填入位置*/
    int  (*inject_location)(double latitude, double longitude, float accuracy);

    /*删除全部or部分辅助数据在性能测试时候使用*/
    void  (*delete_aiding_data)(GpsAidingData flags);

    /*设置定位模式与GPS工作模式等等*/
    int   (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence,
            uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time);

    /*自行添加的接口 AGpsInterface接口通过次函数获得*/
    const void* (*get_extension)(const char* name);
} GpsInterface;
AGpsCallbacks
/** Callback with AGPS status information.
*  Can only be called from a thread created by create_thread_cb.
*/
typedef void (* agps_status_callback)(AGpsStatus* status);

/** Callback structure for the AGPS interface. */
typedef struct {
    agps_status_callback status_cb;
    gps_create_thread create_thread_cb;
} AGpsCallbacks;
AGpsInterface
/** Extended interface for AGPS support. */
typedef struct {
    /** set to sizeof(AGpsInterface) */
    size_t          size;

    /**
     * Opens the AGPS interface and provides the callback routines
     * to the implemenation of this interface.
     */
    void  (*init)( AGpsCallbacks* callbacks );
    /**
     * Notifies that a data connection is available and sets
     * the name of the APN to be used for SUPL.
     */
    int  (*data_conn_open)( const char* apn );
    /**
     * Notifies that the AGPS data connection has been closed.
     */
    int  (*data_conn_closed)();
    /**
     * Notifies that a data connection is not available for AGPS.
     */
    int  (*data_conn_failed)();
    /**
     * Sets the hostname and port for the AGPS server.
     */
    int  (*set_server)( AGpsType type, const char* hostname, int port );
} AGpsInterface
struct gps_device_t
定义描述gps设备类型
struct gps_device_t {
    struct hw_device_t common;

    /**
     * Set the provided lights to the provided values.
     *
     * Returns: 0 on succes, error code on failure.
     */
    const GpsInterface* (*get_gps_interface)(struct gps_device_t* dev);
};
上层会通过动态库，获得此结构，等到GpsInterface从而打通APP到GPS device的全部通信。
还有 GpsNiInterface AGpsRilInterface等接口在此不赘述

基于Android 的GPS 移植

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