3 files changed, 17 insertions, 8 deletions
diff --git a/cores/arduino/WProgram.h b/cores/arduino/WProgram.h
index 206cdac..1fba738 100755
--- a/cores/arduino/WProgram.h
+++ b/cores/arduino/WProgram.h
@@ -10,6 +10,8 @@
 #ifdef __cplusplus
 #include "HardwareSerial.h"
 
+unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout = 1000000L);
+
 // WMath prototypes
 long random(long);
 long random(long, long);
diff --git a/cores/arduino/wiring.h b/cores/arduino/wiring.h
index df43e6c..26cba9e 100755
--- a/cores/arduino/wiring.h
+++ b/cores/arduino/wiring.h
@@ -87,6 +87,7 @@ extern "C"{
 
 #define clockCyclesPerMicrosecond() ( F_CPU / 1000000L )
 #define clockCyclesToMicroseconds(a) ( (a) / clockCyclesPerMicrosecond() )
+#define microsecondsToClockCycles(a) ( (a) * clockCyclesPerMicrosecond() )
 
 typedef uint8_t boolean;
 typedef uint8_t byte;
@@ -118,7 +119,7 @@ void printIntegerInBase(unsigned long n, unsigned long base);
 unsigned long millis(void);
 void delay(unsigned long);
 void delayMicroseconds(unsigned int us);
-unsigned long pulseIn(uint8_t pin, uint8_t state);
+unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout);
 
 void shiftOut(uint8_t dataPin, uint8_t clockPin, uint8_t bitOrder, byte val);
 
diff --git a/cores/arduino/wiring_pulse.c b/cores/arduino/wiring_pulse.c
index 642a5a2..0157114 100755
--- a/cores/arduino/wiring_pulse.c
+++ b/cores/arduino/wiring_pulse.c
@@ -26,10 +26,10 @@
 #include "pins_arduino.h"
 
 /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
- * or LOW, the type of pulse to measure.  Works on pulses from 10 microseconds
- * to 3 minutes in length, but must be called at least N microseconds before
- * the start of the pulse. */
-unsigned long pulseIn(uint8_t pin, uint8_t state)
+ * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
+ * to 3 minutes in length, but must be called at least a few dozen microseconds
+ * before the start of the pulse. */
+unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
 {
 	// cache the port and bit of the pin in order to speed up the
 	// pulse width measuring loop and achieve finer resolution.  calling
@@ -39,17 +39,23 @@ unsigned long pulseIn(uint8_t pin, uint8_t state)
 	uint8_t stateMask = (state ? bit : 0);
 	unsigned long width = 0; // keep initialization out of time critical area
 	
+	// convert the timeout from microseconds to a number of times through
+	// the initial loop; it takes 16 clock cycles per iteration.
+	unsigned long numloops = 0;
+	unsigned long maxloops = microsecondsToClockCycles(timeout) / 16;
+	
 	// wait for the pulse to start
 	while ((*portInputRegister(port) & bit) != stateMask)
-		;
+		if (numloops++ == maxloops)
+			return 0;
 	
 	// wait for the pulse to stop
 	while ((*portInputRegister(port) & bit) == stateMask)
 		width++;
 
 	// convert the reading to microseconds. The loop has been determined
-	// to be 10 clock cycles long and have about 12 clocks between the edge
+	// to be 10 clock cycles long and have about 16 clocks between the edge
 	// and the start of the loop. There will be some error introduced by
 	// the interrupt handlers.
-	return clockCyclesToMicroseconds(width * 10 + 12); 
+	return clockCyclesToMicroseconds(width * 10 + 16); 
 }