Android GPS学习笔记—JNI层实现
2015-06-19 14:51
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Android GPS 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。
目录:
frameworks/base/services/core/jni/com_android_server_location_GpsLocationProvider.cpp
首先来看注册JNI方法的函数定义:
此函数被同目录下onload.cpp文件调用,调用地方在:
从这里可以看到,JNI初始化的时候,即会进行JNI方法的注册,从而使上层应用通过JNI调用C/C++本地的方法
在com_android_server_location_GpsLocationProvider.cpp中,数组sMethods定义如下:
我们来看其中一个本地方法android_location_GpsLocationProvider_start的实现:
以上代码可以看到,函数调用了hw_get_module加载硬件适配模块.so文件,接着通过hw_device_t接口调用open()函数,实际执行了gps/loc_api/libloc_api/gps.c定义的open_gps函数,然后调用gps_device_t接口的get_gps_interface函数,此函数也是在gps.c中定义的,最后返回HAL层中loc_eng.cpp文件的sLocEngInterface,从而打通了上层到底层的通道。
目录:
frameworks/base/services/core/jni/com_android_server_location_GpsLocationProvider.cpp
首先来看注册JNI方法的函数定义:
int register_android_server_location_GpsLocationProvider(JNIEnv* env) { return jniRegisterNativeMethods( env, "com/android/server/location/GpsLocationProvider", sMethods, NELEM(sMethods)); }
此函数被同目录下onload.cpp文件调用,调用地方在:
extern "C" jint JNI_OnLoad(JavaVM* vm, void* reserved) { JNIEnv* env = NULL; jint result = -1; if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) { ALOGE("GetEnv failed!"); return result; } ALOG_ASSERT(env, "Could not retrieve the env!"); //... ...省略其他注册代码 register_android_server_location_GpsLocationProvider(env); return JNI_VERSION_1_4; }
从这里可以看到,JNI初始化的时候,即会进行JNI方法的注册,从而使上层应用通过JNI调用C/C++本地的方法
在com_android_server_location_GpsLocationProvider.cpp中,数组sMethods定义如下:
static JNINativeMethod sMethods[] = { /* name, signature, funcPtr */ {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native}, {"native_is_supported", "()Z", (void*)android_location_GpsLocationProvider_is_supported}, {"native_init", "()Z", (void*)android_location_GpsLocationProvider_init}, {"native_cleanup", "()V", (void*)android_location_GpsLocationProvider_cleanup}, {"native_set_position_mode", "(IIIII)Z", (void*)android_location_GpsLocationProvider_set_position_mode}, {"native_start", "()Z", (void*)android_location_GpsLocationProvider_start}, {"native_stop", "()Z", (void*)android_location_GpsLocationProvider_stop}, {"native_delete_aiding_data", "(I)V", (void*)android_location_GpsLocationProvider_delete_aiding_data}, {"native_read_sv_status", "([I[F[F[F[I)I", (void*)android_location_GpsLocationProvider_read_sv_status}, {"native_read_nmea", "([BI)I", (void*)android_location_GpsLocationProvider_read_nmea}, {"native_inject_time", "(JJI)V", (void*)android_location_GpsLocationProvider_inject_time}, {"native_inject_location", "(DDF)V", (void*)android_location_GpsLocationProvider_inject_location}, {"native_supports_xtra", "()Z", (void*)android_location_GpsLocationProvider_supports_xtra}, {"native_inject_xtra_data", "([BI)V", (void*)android_location_GpsLocationProvider_inject_xtra_data}, {"native_agps_data_conn_open", "(Ljava/lang/String;I)V", (void*)android_location_GpsLocationProvider_agps_data_conn_open}, {"native_agps_data_conn_closed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_closed}, {"native_agps_data_conn_failed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_failed}, {"native_agps_set_id", "(ILjava/lang/String;)V", (void*)android_location_GpsLocationProvider_agps_set_id}, {"native_agps_set_ref_location_cellid", "(IIIII)V", (void*)android_location_GpsLocationProvider_agps_set_reference_location_cellid}, {"native_set_agps_server", "(ILjava/lang/String;I)V", (void*)android_location_GpsLocationProvider_set_agps_server}, {"native_send_ni_response", "(II)V", (void*)android_location_GpsLocationProvider_send_ni_response}, {"native_agps_ni_message", "([BI)V", (void *)android_location_GpsLocationProvider_agps_send_ni_message}, {"native_get_internal_state", "()Ljava/lang/String;", (void*)android_location_GpsLocationProvider_get_internal_state}, {"native_update_network_state", "(ZIZZLjava/lang/String;Ljava/lang/String;)V", (void*)android_location_GpsLocationProvider_update_network_state }, {"native_is_geofence_supported", "()Z", (void*) android_location_GpsLocationProvider_is_geofence_supported}, {"native_add_geofence", "(IDDDIIII)Z", (void *)android_location_GpsLocationProvider_add_geofence}, {"native_remove_geofence", "(I)Z", (void *)android_location_GpsLocationProvider_remove_geofence}, {"native_pause_geofence", "(I)Z", (void *)android_location_GpsLocationProvider_pause_geofence}, {"native_resume_geofence", "(II)Z", (void *)android_location_GpsLocationProvider_resume_geofence}, {"native_is_measurement_supported", "()Z", (void*) android_location_GpsLocationProvider_is_measurement_supported}, {"native_start_measurement_collection", "()Z", (void*) android_location_GpsLocationProvider_start_measurement_collection}, {"native_stop_measurement_collection", "()Z", (void*) android_location_GpsLocationProvider_stop_measurement_collection}, {"native_is_navigation_message_supported", "()Z", (void*) android_location_GpsLocationProvider_is_navigation_message_supported}, {"native_start_navigation_message_collection", "()Z", (void*) android_location_GpsLocationProvider_start_navigation_message_collection}, {"native_stop_navigation_message_collection", "()Z", (void*) android_location_GpsLocationProvider_stop_navigation_message_collection}, {"native_configuration_update", "(Ljava/lang/String;)V", (void*)android_location_GpsLocationProvider_configuration_update}, };这里定义了GPS所有向上层提供的JNI本地方法,这些JNI方法是如何与HAL层交互的呢?
我们来看其中一个本地方法android_location_GpsLocationProvider_start的实现:
static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj) { if (sGpsInterface) { if (sGpsInterface->start() == 0) { return JNI_TRUE; } else { return JNI_FALSE; } } else return JNI_FALSE; }其中,sGpsInterface是在函数android_location_GpsLocationProvider_class_init_native()中通过调用get_gps_interface()获得的GpsInterface接口,获取代码片段如下,函数android_location_GpsLocationProvider_start()直接调用了GpsInterface接口的start回调函数
err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module); if (err == 0) { hw_device_t* device; err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device); if (err == 0) { gps_device_t* gps_device = (gps_device_t *)device; sGpsInterface = gps_device->get_gps_interface(gps_device); } }
以上代码可以看到,函数调用了hw_get_module加载硬件适配模块.so文件,接着通过hw_device_t接口调用open()函数,实际执行了gps/loc_api/libloc_api/gps.c定义的open_gps函数,然后调用gps_device_t接口的get_gps_interface函数,此函数也是在gps.c中定义的,最后返回HAL层中loc_eng.cpp文件的sLocEngInterface,从而打通了上层到底层的通道。
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