android gps hal

Android HAL的实现（1）制作libgps.so库google提供的方法http://source.android.com/porting/gps.html Android.mk:LOCAL_SRC_FILES:= main.c   //指定库的源码LOCAL_MODULE := libgps    //指定库的名称include $(BUILD_SHARED_LIBRARY)    //指定编译成.so库 （2）修改BoardConfig.mk添加BOARD_GPS_LIBRARIES := libgps 由于hardware/libhardware_legacy/gps/Android.mk中指定LOCAL_SHARED_LIBRARIESifneq ($(BOARD_GPS_LIBRARIES),)
  LOCAL_CFLAGS           += -DHAVE_GPS_HARDWARE
  LOCAL_SHARED_LIBRARIES += $(BOARD_GPS_LIBRARIES)
endif （3）修改hardware/libhardware_legacy/gps/gps.cppstaticvoid

gps_find_hardware(void )

{

    sGpsInterface = gps_get_hardware_interface();

    if (!sGpsInterface)

        LOGD("no GPS hardware on this device\n");

}
gps_get_hardware_interface()在libgps.so源码中实现 （4）实现libgps.so源码main.c（可参考hardware/libhardware_legacy/gps/gps_qemu.c） staticconst GpsInterface sirfGpsInterface = {

    sirf_gps_init,

    sirf_gps_start,

    sirf_gps_stop,

    sirf_gps_cleanup,

    sirf_gps_inject_time,

    sirf_gps_inject_location,

    sirf_gps_delete_aiding_data,

    sirf_gps_set_position_mode,

    sirf_gps_get_extension,

};

const GpsInterface* gps_get_hardware_interface()

{

    return &sirfGpsInterface;

}
下面将介绍下需要修改的函数，其他函数都可以仿照gps_qemu.c
sirf_gps_start()函数中添加SiRF_Start()；
sirf_gps_stop()函数中添加SiRF_Stop()；
sirf_gps_init()函数中调用gps_state_init，作用是创建socket通信和gps_state_thread线程；
gps_state_init()函数中需要根据具体的GPS模块实现state->fd = channel_open()；
gps_state_thread()函数中去掉两句nmea_reader_set_callback调用；
nmea_reader_parse()函数添加callbacks.nmea_cb和callbacks.location_cb：
if(r->pos< 9) {

        D("Too short. discarded.");

        return;

}

{

    struct timeval tv;

    gettimeofday(&tv,NULL);

     _gps_state->callbacks.nmea_cb(tv.tv_sec*1000+tv.tv_usec/1000, r->in, r->pos);

}

nmea_tokenizer_init(tzer, r->in, r->in+ r->pos);
if(_gps_state->callbacks.location_cb){

     _gps_state->callbacks.location_cb(&r->fix);

     r->fix.flags= 0;

}

else {

     D("no callback, keeping data until needed !");

}
（5）NMEA数据上报
Android本身的GPS读取NMEA信息机制是调用read函数读取串口信息并解析上报，但SIRF提供了SiRF_Output函数用于底层与应用层的数据上报，GPS工作后会有线程不停调用SiRF_Output，因此只要在SiRF_Output函数中添加：
NmeaReader reader[1];

nmea_reader_init( reader);

for (nn = 0; nn< sizeof(buf); nn++)

     nmea_reader_addc( reader, buf[nn]);
现在GPS可以上报GGA、GSA、RMC等数据（GSA数据需添加nmea_reader_parse函数中关于GSA数据解析）