pulseIn: be consistent with standard API

return 0 if timeout has been reached

Author: facchinm

hardware/arduino/avr/cores/arduino/wiring_pulse.c

@@ -48,7 +48,12 @@ unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
 	unsigned long maxloops = microsecondsToClockCycles(timeout)/16;
 
 	width = countPulseASM(portInputRegister(port), bit, stateMask, maxloops);
-	return clockCyclesToMicroseconds(width * 16 + 16);
+
+	//prevent clockCyclesToMicroseconds to return bogus values if countPulseASM timed out
+	if (width)
+		return clockCyclesToMicroseconds(width * 16 + 16);
+	else
+		return 0;
 }
 
 /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH