Rover: make AUTO_TRIGGER_PIN be a push on/push off

APMrover2/Parameters.pde

@@ -138,7 +138,7 @@ const AP_Param::Info var_info[] PROGMEM = {
 
 	// @Param: AUTO_TRIGGER_PIN
 	// @DisplayName: Auto mode trigger pin
-	// @Description: pin number to use to trigger start of auto mode. If set to -1 then don't use a trigger, otherwise this is a pin number which if held low in auto mode will start the motor.
+	// @Description: pin number to use to trigger start of auto mode. If set to -1 then don't use a trigger, otherwise this is a pin number which if held low in auto mode will start the motor, and otherwise will force the throttle off. This can be used in combination with INITIAL_MODE to give a 'press button to start' rover with no receiver.
 	// @Values: -1:Disabled,0-9:TiggerPin
 	// @User: standard
 	GSCALAR(auto_trigger_pin,        "AUTO_TRIGGER_PIN", -1),

APMrover2/Steering.pde

@@ -27,6 +27,13 @@ static bool auto_check_trigger(void)
         return true;
     }
 
+    // check for user pressing the auto trigger to off
+    if (auto_triggered && g.auto_trigger_pin != -1 && check_digital_pin(g.auto_trigger_pin) == 1) {
+        gcs_send_text_P(SEVERITY_LOW, PSTR("AUTO triggered off"));
+        auto_triggered = false;
+        return false; 
+    }
+
     // if already triggered, then return true, so you don't
     // need to hold the switch down
     if (auto_triggered) {
@@ -39,21 +46,10 @@ static bool auto_check_trigger(void)
         return true;
     }
  
-    if (g.auto_trigger_pin != -1) {
-        int8_t pin = hal.gpio->analogPinToDigitalPin(g.auto_trigger_pin);
-        if (pin != -1) {
-            // ensure we are in input mode
-            hal.gpio->pinMode(pin, GPIO_INPUT);
-
-            // enable pullup
-            hal.gpio->write(pin, 1);
-
-            if (hal.gpio->read(pin) == 0) {
-                gcs_send_text_P(SEVERITY_LOW, PSTR("Triggered AUTO with pin"));
-                auto_triggered = true;
-                return true;            
-            }
-        }
+    if (g.auto_trigger_pin != -1 && check_digital_pin(g.auto_trigger_pin) == 0) {
+        gcs_send_text_P(SEVERITY_LOW, PSTR("Triggered AUTO with pin"));
+        auto_triggered = true;
+        return true;            
     }
 
     if (g.auto_kickstart != 0.0f) {

APMrover2/system.pde

@@ -545,3 +545,21 @@ static void reboot_apm(void)
     hal.scheduler->reboot();
     while (1);
 }
+
+/*
+  check a digitial pin for high,low (1/0)
+ */
+static uint8_t check_digital_pin(uint8_t pin)
+{
+    int8_t dpin = hal.gpio->analogPinToDigitalPin(pin);
+    if (dpin == -1) {
+        return 0;
+    }
+    // ensure we are in input mode
+    hal.gpio->pinMode(dpin, GPIO_INPUT);
+
+    // enable pullup
+    hal.gpio->write(dpin, 1);
+
+    return hal.gpio->read(dpin);
+}