APM: added RST_SWITCH_CH parameter

This is useful for switching back to the mode indicated by the control
switch after a failsafe or fence breach. I was just changing modes
each time, but it is far more elegant to have a spring loaded switch
for "I am ready to take control again", rather than continually
changing modes.

ArduPlane/Parameters.h

@@ -70,6 +70,7 @@ public:
         k_param_flap_2_speed,
         k_param_num_resets,
         k_param_log_last_filenumber,		// *** Deprecated - remove with next eeprom number change
+        k_param_reset_switch_chan,
 
 
 		// 110: Telemetry control
@@ -320,6 +321,7 @@ public:
     AP_Int16    num_resets;
     AP_Int16    log_bitmask;
     AP_Int16	log_last_filenumber;		// *** Deprecated - remove with next eeprom number change
+    AP_Int8		reset_switch_chan;
     AP_Int16    airspeed_cruise;
     AP_Int16    min_gndspeed;
     AP_Int16    pitch_trim;
@@ -435,6 +437,7 @@ public:
         num_resets              (0,                         k_param_num_resets,             PSTR("SYS_NUM_RESETS")),
         log_bitmask             (DEFAULT_LOG_BITMASK,		k_param_log_bitmask,            PSTR("LOG_BITMASK")),
         log_last_filenumber     (0,							k_param_log_last_filenumber,    PSTR("LOG_LASTFILE")),
+        reset_switch_chan		(0,							k_param_reset_switch_chan,		PSTR("RST_SWITCH_CH")),
         airspeed_cruise         (AIRSPEED_CRUISE_CM,        k_param_airspeed_cruise,        PSTR("TRIM_ARSPD_CM")),
         min_gndspeed            (MIN_GNDSPEED_CM,        	k_param_min_gndspeed,           PSTR("MIN_GNDSPD_CM")),
         pitch_trim              (0,                         k_param_pitch_trim,             PSTR("TRIM_PITCH_CD")),

ArduPlane/config.h

@@ -816,3 +816,11 @@
 #ifndef FENCE_TRIGGERED_PIN
 # define FENCE_TRIGGERED_PIN -1
 #endif
+
+// if RESET_SWITCH_CH is not zero, then this is the PWM value on
+// that channel where we reset the control mode to the current switch
+// position (to for example return to switched mode after failsafe or
+// fence breach)
+#ifndef RESET_SWITCH_CHAN_PWM
+# define RESET_SWITCH_CHAN_PWM 1750
+#endif

ArduPlane/control_modes.pde

@@ -3,7 +3,16 @@
 static void read_control_switch()
 {
 	byte switchPosition = readSwitch();
-	if (oldSwitchPosition != switchPosition){
+
+    // we look for changes in the switch position. If the
+    // RST_SWITCH_CH parameter is set, then it is a switch that can be
+    // used to force re-reading of the control switch. This is useful
+    // when returning to the previous mode after a failsafe or fence
+    // breach. This channel is best used on a momentary switch (such
+    // as a spring loaded trainer switch).
+	if (oldSwitchPosition != switchPosition ||
+        (g.reset_switch_chan != 0 && 
+         APM_RC.InputCh(g.reset_switch_chan-1) > RESET_SWITCH_CHAN_PWM)) {
 
 		set_mode(flight_modes[switchPosition]);