From 4f80fe1489bcb3ed3b1ac8c741d2d71583c838ce Mon Sep 17 00:00:00 2001
From: "David A. Mellis" <d.mellis@arduino.cc>
Date: Fri, 24 Mar 2006 14:09:54 +0000
Subject: [PATCH] Added pulseIn function to measure pulse durations.

---
 targets/arduino/wiring.c | 33 +++++++++++++++++++++++++++++++++
 targets/arduino/wiring.h |  1 +
 2 files changed, 34 insertions(+)

diff --git a/targets/arduino/wiring.c b/targets/arduino/wiring.c
index a8faa3752..3b93286d7 100755
--- a/targets/arduino/wiring.c
+++ b/targets/arduino/wiring.c
@@ -366,6 +366,39 @@ void delayMicroseconds(unsigned int us)
 	sei();
 }
 
+/*
+unsigned long pulseIn(int pin, int state)
+{
+	unsigned long width = 0;
+
+	while (digitalRead(pin) == !state)
+		;
+		
+	while (digitalRead(pin) != !state)
+		width++;
+		
+	return width * 17 / 2; // convert to microseconds
+}
+*/
+
+unsigned long pulseIn(int pin, int state)
+{
+	unsigned long width = 0;
+	int r = port_to_input[digitalPinToPort(pin)];
+	int bit = digitalPinToBit(pin);
+	int mask = 1 << bit;
+
+	state = (!!state) << bit;
+
+	while ((_SFR_IO8(r) & mask) != state)
+		;
+		
+	while ((_SFR_IO8(r) & mask) == state)
+		width++;
+		
+	return width * (16000000UL / F_CPU) * 20 / 23;
+}
+
 int main(void)
 {
 	// this needs to be called before setup() or some functions won't
diff --git a/targets/arduino/wiring.h b/targets/arduino/wiring.h
index 6cbfd132e..2b55c4d4c 100755
--- a/targets/arduino/wiring.h
+++ b/targets/arduino/wiring.h
@@ -82,6 +82,7 @@ unsigned long millis(void);
 void delay(unsigned long);
 void delay_ms(unsigned short ms);
 void delayMicroseconds(unsigned int us);
+unsigned long pulseIn(int pin, int state);
 
 void setup(void);
 void loop(void);