Do not auto-attach interrupt on construction

This was causing issues on certain platforms where the platform's interrupt attachment system was not set up or available when the object was constructed in global scope (see dmadison#28).

Instead, the user must attach() the object themselves before they can read signals. The library examples have been updated accordingly.

examples/BasicAngle/BasicAngle.ino

@@ -38,6 +38,7 @@ ServoInputPin<2> servo;
 
 void setup() {
 	Serial.begin(115200);
+	servo.attach();  // attaches the servo input interrupt
 
 	while (servo.available() == false) {
 		Serial.println("Waiting for servo signal...");

examples/Calibration/Calibration.ino

@@ -40,6 +40,7 @@ ServoInputPin<2> servo;
 
 void setup() {
 	Serial.begin(115200);
+	servo.attach();  // attaches the servo input interrupt
 
 	int center = servo.getRangeCenter();  // get center value of range
 	servo.setRange(center, center);  // set min/max values to center

examples/Loopback/Loopback.ino

@@ -49,6 +49,7 @@ int waitTime = 10;  // milliseconds (ms)
 void setup() {
 	Serial.begin(115200);
 
+	inputServo.attach();  // attaches the servo input interrupt
 	outputServo.attach(OutputPin);  // attaches the servo on pin 9 to the servo object
 
 	while (inputServo.available() == false) {

examples/PinChangeInt/PinChange/PinChange.ino

@@ -60,6 +60,8 @@ ISR(PCINT0_vect) {  // pin change ISR handler for Arduino Uno pins D8 - D13
 void setup() {
 	Serial.begin(115200);
 
+	// note that we do *not* need to call servo.attach(), because we are
+	// using our own custom interrupt service routine (ISR)
 	setInterrupt();  // set pin change interrupt (see above)
 
 	while (servo.available() == false) {

examples/PinChangeInt/PinChangeLib/PinChangeLib.ino

@@ -53,6 +53,8 @@ ServoInputPin<pin2> servo2;
 
 void setup() {
 	Serial.begin(115200);
+	servo1.attach();  // attaches the first servo input interrupt
+	servo2.attach();  // attaches the second servo input interrupt
 
 	// wait for all servo signals to be read for the first time
 	while (!ServoInput.available()) {

examples/RC_Receiver/RC_Receiver.ino

@@ -53,6 +53,8 @@ ServoInputPin<ThrottleSignalPin> throttle(ThrottlePulseMin, ThrottlePulseMax);
 
 void setup() {
 	Serial.begin(115200);
+	steering.attach();  // attaches the steering servo input interrupt
+	throttle.attach();  // attaches the throttle servo input interrupt
 
 	while (!ServoInput.available()) {  // wait for all signals to be ready
 		Serial.println("Waiting for servo signals...");

examples/Remapping/Remapping.ino

@@ -38,6 +38,7 @@ ServoInputPin<2> servo;
 
 void setup() {
 	Serial.begin(115200);
+	servo.attach();  // attaches the servo input interrupt
 
 	while (servo.available() == false) {
 		Serial.println("Waiting for servo signal...");

src/ServoInput.h

@@ -96,7 +96,6 @@ class ServoInputPin : public ServoInputSignal {
 			ServoInputPin<Pin>::PortRegister = SERVOINPUT_PIN_TO_BASEREG(Pin);
 		#endif
 		pinMode(Pin, INPUT_PULLUP);
-		attach();
 	}
 
 	ServoInputPin(uint16_t pMin, uint16_t pMax) : ServoInputPin() {