AP_AnalogSource: added set_pin() interface

this allows pin numbers to be changed at runtime

libraries/AP_AnalogSource/AP_AnalogSource_Arduino.cpp

@@ -131,17 +131,9 @@ float AP_AnalogSource_Arduino::read(void)
 }
 
 
-// assign a slot in the pins_watched
-void AP_AnalogSource_Arduino::assign_pin_index(uint8_t pin)
+// remap pin numbers to physical pin
+uint8_t AP_AnalogSource_Arduino::_remap_pin(uint8_t pin)
 {
-    // ensure we don't try to read from too many analog pins
-    if (num_pins_watched == MAX_PIN_SOURCES) {
-        while (true) {
-            Serial.printf_P(PSTR("MAX_PIN_SOURCES REACHED\n"));
-            delay(1000);
-        }
-    }
-
     if (pin != ANALOG_PIN_VCC) {
         // allow pin to be a channel (i.e. "A0") or an actual pin
 #if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
@@ -154,7 +146,21 @@ void AP_AnalogSource_Arduino::assign_pin_index(uint8_t pin)
         if (pin >= 14) pin -= 14;
 #endif
     }
+    return pin;
+}
+
+// assign a slot in the pins_watched
+void AP_AnalogSource_Arduino::_assign_pin_index(uint8_t pin)
+{
+    // ensure we don't try to read from too many analog pins
+    if (num_pins_watched == MAX_PIN_SOURCES) {
+        while (true) {
+            Serial.printf_P(PSTR("MAX_PIN_SOURCES REACHED\n"));
+            delay(1000);
+        }
+    }
 
+    pin = _remap_pin(pin);
     _pin_index = num_pins_watched;
     pins[_pin_index].pin = pin;
     num_pins_watched++;
@@ -164,3 +170,16 @@ void AP_AnalogSource_Arduino::assign_pin_index(uint8_t pin)
         ADCSRA |= _BV(ADEN);
     }
 }
+
+// change which pin to read
+void AP_AnalogSource_Arduino::set_pin(uint8_t pin)
+{
+    pin = _remap_pin(pin);
+    if (pins[_pin_index].pin != pin) {
+        cli();
+        pins[_pin_index].pin = pin;
+        pins[_pin_index].sum = 0;
+        pins[_pin_index].sum_count = 0;
+        sei();        
+    }
+}

libraries/AP_AnalogSource/AP_AnalogSource_Arduino.h

@@ -15,7 +15,7 @@ class AP_AnalogSource_Arduino : public AP_AnalogSource
 public:
     AP_AnalogSource_Arduino( uint8_t pin, float prescale = 1.0 ) :
         _prescale(prescale) {
-        assign_pin_index(pin);
+        _assign_pin_index(pin);
     }
 
     // setup the timer callback
@@ -34,11 +34,16 @@ public:
     // we last called read_average().
     float           read_average(void);
 
+    // set the pin to be used for this source. This allows for the pin
+    // to be changed at runtime
+    void set_pin(uint8_t pin);
+
 private:
     uint8_t         _pin_index;
     float           _prescale;
 
-    void            assign_pin_index(uint8_t pin);
+    uint8_t         _remap_pin(uint8_t pin);
+    void            _assign_pin_index(uint8_t pin);
 };
 
 #endif // __AP_ANALOG_SOURCE_ARDUINO_H__