Android App to HAL Code Flow

===================== GPS :: Flow from FW to HAL ===========================
App ==> FW java ==> JNI ==> HAL ==> kernel

Framework Java:-

/frameworks/base/services/core/java/com/android/server/location/GpsLocationProvider.java

Code:-
public class GpsLocationProvider implements LocationProviderInterface {
private native void native_inject_time(long time, long timeReference, int uncertainty);
}

*********************************************************************************
JNI Layer:-
/frameworks/base/services/core/jni/com_android_server_location_GpsLocationProvider.cpp
Code:-
/* Native method registration Start */
static JNINativeMethod sMethods[] = {
{"native_inject_time", "(JJI)V", (void*)android_location_GpsLocationProvider_inject_time},
......
}

Above method once registered java can call these methods,
int register_android_server_location_GpsLocationProvider(JNIEnv* env)
{
return jniRegisterNativeMethods(
env,
"com/android/server/location/GpsLocationProvider",
sMethods,
NELEM(sMethods));
}
/* Native method registration End */

/* Get the HAL module here start */
    err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);

/* Search the HAl module with the below macro name */
/hardware/libhardware/include/hardware/gps.h
#define GPS_HARDWARE_MODULE_ID "gps"

/* Call HAL module device open */
err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);

/* The below open method will get called */
loc_api/libloc_api_50001/gps.c
static struct hw_module_methods_t gps_module_methods = {
.open = open_gps
};
gps_device_t* gps_device = (gps_device_t *)device;
    sGpsInterface = gps_device->get_gps_interface(gps_device);

*********************************************************************************
HAL Layer:-

[1]
/hardware/qcom/gps/msm8084/loc_api/libloc_api_50001/loc.cpp
extern "C" const GpsInterface* get_gps_interface() {

return &sLocEngInterface; // See below the
}

// Defines the GpsInterface in gps.h
static const GpsInterface sLocEngInterface =
{
   sizeof(GpsInterface),
   loc_init,
   loc_start,
   loc_stop,
   loc_cleanup,
   loc_inject_time,
   loc_inject_location,
   loc_delete_aiding_data,
   loc_set_position_mode,
   loc_get_extension
};
The above structure is defined in hardware/libhardware/include/hardware/gps.h

Now when u call sGpsInterface->init(&sGpsCallbacks) from JNI above loc_init() fn will get called

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