android GPS HAL 回调函数实现

实现自己的GPS的HAL层，要实现gps.c文件，（按照Android系统的调用）参考 http://blog.chinaunix.net/uid-25570748-id-184090.html分析的很好。

const struct hw_module_t HAL_MODULE_INFO_SYM = { . tag = HARDWARE_MODULE_TAG , . version_major = 1 , . version_minor = 0 , . id = GPS_HARDWARE_MODULE_ID , . name = "Goldfish GPS Module" , . author = "The Android Open Source Project" , . methods = & gps_module_methods , };

static struct hw_module_methods_t gps_module_methods = { . open = open_gps };

static int o pen_gps ( const struct hw_module_t * module , char const * name , struct hw_device_t ** device ) { struct gps_device_t * dev = malloc ( sizeof ( struct gps_device_t )); memset ( dev , 0 , sizeof (* dev )); D ( "%s: called\n" , __FUNCTION__ ); dev -> common . tag = HARDWARE_DEVICE_TAG ; dev -> common . version = 0 ; dev -> common . module = ( struct hw_module_t *) module ; // dev->common.close = (int (*)(struct hw_device_t*))close_lights; dev->get_gps_interface = gps__get_gps_interface ;
*device = ( struct hw_device_t *) dev ; return 0 ; }

const GpsInterface * gps__get_gps_interface ( struct gps_device_t * dev ) { D ( "%s: called\n" , __FUNCTION__ ); return & sepGpsInterface ; }

static const GpsInterface sepGpsInterface = { sizeof ( GpsInterface ), sep_gps_init , sep_gps_start , sep_gps_stop , sep_gps_cleanup , sep_gps_inject_time , sep_gps_inject_location , sep_gps_delete_aiding_data , sep_gps_set_position_mode , sep_gps_get_extension , }；

这里的GpsInterface定义如下，在hardware/libhardware/include/hardware/gps.h文件中

/** Represents the standard GPS interface. */
typedef struct {
size_t size;
int (*init)( GpsCallbacks* callbacks );
int (*start)( void );
int (*stop)( void );
void (*cleanup)( void );
int (*inject_time)(GpsUtcTime time, int64_t timeReference, int uncertainty);
int (*inject_location)(double latitude, double longitude, float accuracy);
void (*delete_aiding_data)(GpsAidingData flags);
int (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence,
uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time);
const void* (*get_extension)(const char* name);
} GpsInterface;

/** 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; 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;

比如说GpsInterface里面init函数，需要一个参数，callbacks，没有发现哪里有对回调函数的定义。有读了一遍别人的博客的分析 http://blog.chinaunix.net/uid-25570748-id-184090.html GPS服务启动的过程中，在JNI层会去初始化GPS com_android_server_location_GpsLocationProvider.cpp文件中的ini函数

static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj) { const GpsInterface* interface = GetGpsInterface(env, obj); if (!interface) return false; if (!sGpsDebugInterface) sGpsDebugInterface = (const GpsDebugInterface*)interface->get_extension(GPS_DEBUG_INTERFACE); return true; }

调用了GetGpsInterface去获取接口并初始化GPS

static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) { // this must be set before calling into the HAL library if (!mCallbacksObj) mCallbacksObj = env->NewGlobalRef(obj); if (!sGpsInterface) { sGpsInterface = get_gps_interface(); if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) { sGpsInterface = NULL; return NULL; } } return sGpsInterface; }

GetGpsInterface里面也去调用了get_gps_interface()，而这个函数最早的地方便是isSupported()的这个函数。在获取了这个接口之后，使用sGpsInterface->init函数进行了初始化。原来是在这里注册了回调函数。 sGpsCallbacks是个全局变量，在com_android_server_location_GpsLocationProvider.cpp文件中

GpsCallbacks sGpsCallbacks = { sizeof ( GpsCallbacks ), location_callback , status_callback , sv_status_callback , nmea_callback , set_capabilities_callback , acquire_wakelock_callback , release_wakelock_callback , create_thread_callback , }; 然后，也有各个回调函数的实现

static void location_callback ( GpsLocation * location ) { JNIEnv * env = AndroidRuntime :: getJNIEnv (); env -> CallVoidMethod ( mCallbacksObj , method_reportLocation , location -> flags , (jdouble ) location -> latitude , ( jdouble ) location -> longitude , (jdouble ) location -> altitude , (jfloat ) location -> speed , ( jfloat ) location -> bearing , (jfloat ) location -> accuracy , ( jlong ) location -> timestamp ); checkAndClearExceptionFromCallback ( env , __FUNCTION__ ); }

static void status_callback ( GpsStatus * status ) { JNIEnv * env = AndroidRuntime :: getJNIEnv (); env -> CallVoidMethod ( mCallbacksObj , method_reportStatus , status -> status ); checkAndClearExceptionFromCallback ( env , __FUNCTION__ ); }

static void sv_status_callback ( GpsSvStatus * sv_status ) { JNIEnv * env = AndroidRuntime :: getJNIEnv (); memcpy (& sGpsSvStatus , sv_status , sizeof ( sGpsSvStatus )); env -> CallVoidMethod ( mCallbacksObj , method_reportSvStatus ); checkAndClearExceptionFromCallback ( env , __FUNCTION__ ); }

static void nmea_callback ( GpsUtcTime timestamp , const char * nmea , int length ) { JNIEnv * env = AndroidRuntime :: getJNIEnv (); // The Java code will call back to read these values // We do this to avoid creating unnecessary String objects sNmeaString = nmea; sNmeaStringLength = length; env->CallVoidMethod(mCallbacksObj, method_reportNmea, timestamp); checkAndClearExceptionFromCallback(env, __FUNCTION__); }

static void set_capabilities_callback ( uint32_t capabilities ) { LOGD ( "set_capabilities_callback: %ld\n" , capabilities ); JNIEnv * env = AndroidRuntime :: getJNIEnv (); env -> CallVoidMethod ( mCallbacksObj , method_setEngineCapabilities , capabilities ); checkAndClearExceptionFromCallback ( env , __FUNCTION__ ); }

static void acquire_wakelock_callback () {    acquire_wake_lock ( PARTIAL_WAKE_LOCK , WAKE_LOCK_NAME ); }
static void release_wakelock_callback () {    release_wake_lock ( WAKE_LOCK_NAME ); }
static pthread_t create_thread_callback ( const char * name , void (* start )( void *), void * arg ) {    return ( pthread_t ) AndroidRuntime :: createJavaThread ( name , start , arg ); }

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