Plane: fixed mixer arming error with FMUv4

thanks to Tim Gold for reporting this

ArduPlane/ArduPlane.cpp

@@ -308,7 +308,7 @@ void Plane::one_second_loop()
     // make it possible to change control channel ordering at runtime
     set_control_channels();
 
-#if CONFIG_HAL_BOARD == HAL_BOARD_PX4
+#if HAVE_PX4_MIXER
     if (!hal.util->get_soft_armed() && (last_mixer_crc == -1)) {
         // if disarmed try to configure the mixer
         setup_failsafe_mixing();

ArduPlane/Parameters.cpp

@@ -1009,7 +1009,7 @@ const AP_Param::Info Plane::var_info[] = {
     // @User: Advanced
     GSCALAR(land_flap_percent,     "LAND_FLAP_PERCNT", 0),
 
-#if CONFIG_HAL_BOARD == HAL_BOARD_PX4
+#if HAVE_PX4_MIXER
     // @Param: OVERRIDE_CHAN
     // @DisplayName: PX4IO override channel
     // @Description: If set to a non-zero value then this is an RC input channel number to use for giving PX4IO manual control in case the main FMU microcontroller on a PX4 or Pixhawk fails. When this RC input channel goes above 1750 the FMU microcontroller will no longer be involved in controlling the servos and instead the PX4IO microcontroller will directly control the servos. Note that PX4IO manual control will be automatically activated if the FMU crashes for any reason. This parameter allows you to test for correct manual behaviour without actually crashing the FMU. This parameter is can be set to a non-zero value either for ground testing purposes or for giving the effect of an external override control board. Please also see the docs on OVERRIDE_SAFETY. Note that you may set OVERRIDE_CHAN to the same channel as FLTMODE_CH to get PX4IO based override when in flight mode 6. Note that when override is triggered due to a FMU crash the 6 auxiliary output channels on Pixhawk will no longer be updated, so all the flight controls you need must be assigned to the first 8 channels.

ArduPlane/arming_checks.cpp

@@ -83,7 +83,7 @@ bool AP_Arming_Plane::pre_arm_checks(bool report)
         ret = false;
     }
 
-#if CONFIG_HAL_BOARD == HAL_BOARD_PX4
+#if HAVE_PX4_MIXER
     if (plane.last_mixer_crc == -1) {
         if (report) {
             // if you ever get this error, a reboot is recommended.

ArduPlane/config.h

@@ -412,3 +412,10 @@
 #ifndef PARACHUTE
 #define PARACHUTE ENABLED
 #endif
+
+#if CONFIG_HAL_BOARD == HAL_BOARD_PX4 && !defined(CONFIG_ARCH_BOARD_PX4FMU_V4)
+# define HAVE_PX4_MIXER 1
+#else
+# define HAVE_PX4_MIXER 0
+#endif
+

ArduPlane/control_modes.cpp

@@ -68,7 +68,7 @@ void Plane::read_control_switch()
     }
 #endif
     
-#if CONFIG_HAL_BOARD == HAL_BOARD_PX4
+#if HAVE_PX4_MIXER
     if (g.override_channel > 0) {
         // if the user has configured an override channel then check it
         bool override_requested = (hal.rcin->read(g.override_channel-1) >= PX4IO_OVERRIDE_PWM);
@@ -97,7 +97,7 @@ void Plane::read_control_switch()
             hal.rcout->force_safety_off();
         }
     }
-#endif // CONFIG_HAL_BOARD
+#endif // HAVE_PX4_MIXER
 }
 
 uint8_t Plane::readSwitch(void)

ArduPlane/px4_mixer.cpp

@@ -12,7 +12,7 @@
   that include flaps, landing gear, ignition cut etc
  */
 
-#if CONFIG_HAL_BOARD == HAL_BOARD_PX4
+#if HAVE_PX4_MIXER
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>

ArduPlane/quadplane.cpp

@@ -462,7 +462,7 @@ bool QuadPlane::setup(void)
         }
     }
 
-#if CONFIG_HAL_BOARD == HAL_BOARD_PX4
+#if HAVE_PX4_MIXER
     // redo failsafe mixing on px4
     plane.setup_failsafe_mixing();
 #endif

ArduPlane/system.cpp

@@ -102,7 +102,7 @@ void Plane::init_ardupilot()
     set_control_channels();
     init_rc_out_main();
     
-#if CONFIG_HAL_BOARD == HAL_BOARD_PX4
+#if HAVE_PX4_MIXER
     if (!quadplane.enable) {
         // this must be before BoardConfig.init() so if
         // BRD_SAFETYENABLE==0 then we don't have safety off yet. For