diff --git a/conf/firmwares/subsystems/fixedwing/ins_vectornav.makefile b/conf/firmwares/subsystems/fixedwing/ins_vectornav.makefile
index ce86af8221..ddeef1b323 100644
--- a/conf/firmwares/subsystems/fixedwing/ins_vectornav.makefile
+++ b/conf/firmwares/subsystems/fixedwing/ins_vectornav.makefile
@@ -19,7 +19,7 @@ sim.CFLAGS += -DINS_TYPE_H=\"subsystems/ins/ins_gps_passthrough_utm.h\"
 sim.srcs   += $(SRC_SUBSYSTEMS)/ins/ins_gps_passthrough_utm.c
 
 sim.CFLAGS += -DUSE_GPS
-sim.CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+sim.CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 sim.srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 sim.srcs += $(SRC_SUBSYSTEMS)/gps.c
 
diff --git a/conf/firmwares/subsystems/fixedwing/ins_xsens.makefile b/conf/firmwares/subsystems/fixedwing/ins_xsens.makefile
index c243ad9f96..7c5c390035 100644
--- a/conf/firmwares/subsystems/fixedwing/ins_xsens.makefile
+++ b/conf/firmwares/subsystems/fixedwing/ins_xsens.makefile
@@ -62,7 +62,7 @@ $(TARGET).CFLAGS += -DINS_TYPE_H=\"subsystems/ins/ins_gps_passthrough_utm.h\"
 $(TARGET).srcs   += $(SRC_SUBSYSTEMS)/ins/ins_gps_passthrough_utm.c
 
 $(TARGET).CFLAGS += -DUSE_GPS
-$(TARGET).CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+$(TARGET).CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps.c
 
diff --git a/conf/firmwares/subsystems/rotorcraft/gps_ardrone2.makefile b/conf/firmwares/subsystems/rotorcraft/gps_ardrone2.makefile
index 49de927e45..96d287b32d 100644
--- a/conf/firmwares/subsystems/rotorcraft/gps_ardrone2.makefile
+++ b/conf/firmwares/subsystems/rotorcraft/gps_ardrone2.makefile
@@ -16,6 +16,6 @@ ap.srcs   += $(SRC_SUBSYSTEMS)/gps/gps_ardrone2.c
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps.c
 
 nps.CFLAGS += -DUSE_GPS
-nps.CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+nps.CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 nps.srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim_nps.c
 
diff --git a/conf/firmwares/subsystems/shared/gps_furuno.makefile b/conf/firmwares/subsystems/shared/gps_furuno.makefile
index 648cf1d7f2..430720e43c 100644
--- a/conf/firmwares/subsystems/shared/gps_furuno.makefile
+++ b/conf/firmwares/subsystems/shared/gps_furuno.makefile
@@ -21,7 +21,7 @@ ap.srcs   += $(SRC_SUBSYSTEMS)/gps/gps_nmea.c $(SRC_SUBSYSTEMS)/gps/gps_furuno.c
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps.c
 
 sim.CFLAGS += -DUSE_GPS
-sim.CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+sim.CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 sim.srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 
 nps.CFLAGS += -DUSE_GPS
diff --git a/conf/firmwares/subsystems/shared/gps_mediatek_diy.makefile b/conf/firmwares/subsystems/shared/gps_mediatek_diy.makefile
index 8136a07739..2d2bdd8c0f 100644
--- a/conf/firmwares/subsystems/shared/gps_mediatek_diy.makefile
+++ b/conf/firmwares/subsystems/shared/gps_mediatek_diy.makefile
@@ -20,7 +20,7 @@ ap.srcs   += $(SRC_SUBSYSTEMS)/gps/gps_mtk.c
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps.c
 
 sim.CFLAGS += -DUSE_GPS
-sim.CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+sim.CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 sim.srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 
 nps.CFLAGS += -DUSE_GPS
diff --git a/conf/firmwares/subsystems/shared/gps_nmea.makefile b/conf/firmwares/subsystems/shared/gps_nmea.makefile
index 986259fbbc..5340a29afe 100644
--- a/conf/firmwares/subsystems/shared/gps_nmea.makefile
+++ b/conf/firmwares/subsystems/shared/gps_nmea.makefile
@@ -20,7 +20,7 @@ ap.srcs   += $(SRC_SUBSYSTEMS)/gps/gps_nmea.c
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps.c
 
 sim.CFLAGS += -DUSE_GPS
-sim.CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+sim.CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 sim.srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 
 nps.CFLAGS += -DUSE_GPS
diff --git a/conf/firmwares/subsystems/shared/gps_piksi.makefile b/conf/firmwares/subsystems/shared/gps_piksi.makefile
index c33a56f981..d910ecbf8f 100644
--- a/conf/firmwares/subsystems/shared/gps_piksi.makefile
+++ b/conf/firmwares/subsystems/shared/gps_piksi.makefile
@@ -24,7 +24,7 @@ ap.CFLAGS += -I$(PAPARAZZI_SRC)/sw/ext/libsbp/c/include
 ap.srcs		+= $(PAPARAZZI_SRC)/sw/ext/libsbp/c/src/sbp.c $(PAPARAZZI_SRC)/sw/ext/libsbp/c/src/edc.c
 
 sim.CFLAGS += -DUSE_GPS
-sim.CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+sim.CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 sim.srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 
 nps.CFLAGS += -DUSE_GPS
diff --git a/conf/firmwares/subsystems/shared/gps_ublox.makefile b/conf/firmwares/subsystems/shared/gps_ublox.makefile
index e6a00512a2..4c5c6996b3 100644
--- a/conf/firmwares/subsystems/shared/gps_ublox.makefile
+++ b/conf/firmwares/subsystems/shared/gps_ublox.makefile
@@ -19,7 +19,7 @@ ap.srcs   += $(SRC_SUBSYSTEMS)/gps/gps_ubx.c
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps.c
 
 sim.CFLAGS += -DUSE_GPS
-sim.CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+sim.CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 sim.srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 
 nps.CFLAGS += -DUSE_GPS
diff --git a/conf/firmwares/subsystems/shared/ins_xsens700.makefile b/conf/firmwares/subsystems/shared/ins_xsens700.makefile
index 58be4d9d3f..a1a886835b 100644
--- a/conf/firmwares/subsystems/shared/ins_xsens700.makefile
+++ b/conf/firmwares/subsystems/shared/ins_xsens700.makefile
@@ -56,7 +56,7 @@ $(TARGET).CFLAGS += -DINS_TYPE_H=\"subsystems/ins/ins_gps_passthrough_utm.h\"
 $(TARGET).srcs   += $(SRC_SUBSYSTEMS)/ins/ins_gps_passthrough_utm.c
 
 $(TARGET).CFLAGS += -DUSE_GPS
-$(TARGET).CFLAGS += -DGPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
+$(TARGET).CFLAGS += -DPRIMARY_GPS_TYPE_H=\"subsystems/gps/gps_sim.h\"
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps/gps_sim.c
 $(TARGET).srcs += $(SRC_SUBSYSTEMS)/gps.c
 
diff --git a/sw/airborne/subsystems/gps/gps_sim.c b/sw/airborne/subsystems/gps/gps_sim.c
index 1174c883b6..9887099f08 100644
--- a/sw/airborne/subsystems/gps/gps_sim.c
+++ b/sw/airborne/subsystems/gps/gps_sim.c
@@ -19,14 +19,18 @@
  * Boston, MA 02111-1307, USA.
  */
 
-#include "subsystems/gps.h"
+#include "subsystems/gps/gps_sim.h"
 #include "subsystems/abi.h"
 
-void gps_impl_init(void)
+void sim_gps_impl_init(void)
 {
   gps.fix = GPS_FIX_NONE;
 }
 
+void sim_gps_event(void)
+{
+}
+
 void gps_sim_publish(void)
 {
   uint32_t now_ts = get_sys_time_usec();
@@ -38,3 +42,11 @@ void gps_sim_publish(void)
   }
   AbiSendMsgGPS(GPS_SIM_ID, now_ts, &gps);
 }
+
+/*
+ * register callbacks & structs
+ */
+void sim_gps_register(void)
+{
+  gps_register_impl(sim_gps_impl_init, sim_gps_event, GPS_SIM_ID, 0);
+}
diff --git a/sw/airborne/subsystems/gps/gps_sim.h b/sw/airborne/subsystems/gps/gps_sim.h
index b7012d92d5..7c8523e145 100644
--- a/sw/airborne/subsystems/gps/gps_sim.h
+++ b/sw/airborne/subsystems/gps/gps_sim.h
@@ -2,13 +2,19 @@
 #define GPS_SIM_H
 
 #include "std.h"
+#include "subsystems/gps.h"
 
-#define GPS_NB_CHANNELS 16
-
-extern void gps_impl_init(void);
+// #define GPS_NB_CHANNELS 16
+#ifndef PrimaryGpsImpl
+#define PrimaryGpsImpl sim
+#endif
 
 extern void gps_sim_publish(void);
 
-#define GpsEvent() {}
+extern void sim_gps_event(void);
+extern void sim_gps_impl_init(void);
+extern void sim_gps_register(void);
+
+// #define GpsEvent() {}
 
 #endif /* GPS_SIM_H */