NXPhlite work arround to internal i2c routed to external connector.

   Since the only device on the bus is the barro, int or ext does
   not apply. This will be fixed on the rev > RC15.
   This defines an alias that can be used to condition the buss logic
   connection logic px4_i2c_bus_external to return external.

ROMFS/px4fmu_common/init.d/rc.sensors

@@ -107,8 +107,11 @@ fi
 
 if ver hwcmp NXPHLITE_V3
 then
-	# Internal I2C (baro)
-	mpl3115a2 -I start
+	# External I2C bus
+	hmc5883 -C -X start
+
+	# Onboard I2C (baro) but an external bus on V3 RC15
+	mpl3115a2 -X start
 
 	# Internal SPI (accel + mag)
 	fxos8701cq start -a 8 -R 0

src/drivers/boards/nxphlite-v3/board_config.h

@@ -259,9 +259,9 @@ __BEGIN_DECLS
 /* I2C busses */
 
 #define PX4_I2C_BUS_EXPANSION               PX4_BUS_NUMBER_TO_PX4(0)
-#define PX4_I2C_BUS_ONBOARD                 PX4_BUS_NUMBER_TO_PX4(1)
-
-#define PX4_I2C_BUS_LED                     PX4_I2C_BUS_EXPANSION
+#define PX4_I2C_BUS_EXPANSION1              PX4_BUS_NUMBER_TO_PX4(1) // V3 RC15 has mpl3115a2 on onboard but this goes to a connector
+// So it is treated as external.
+#define PX4_I2C_BUS_LED                     PX4_I2C_BUS_EXPANSION1
 
 /*
  * ADC channels