From 051eb371a6c277a9df95fd88f8a5abdd7fa60440 Mon Sep 17 00:00:00 2001
From: "David A. Mellis" <d.mellis@arduino.cc>
Date: Wed, 26 Nov 2008 14:14:59 +0000
Subject: [PATCH] Adding micros() function.

---
 cores/arduino/wiring.c | 17 +++++++++++++++++
 cores/arduino/wiring.h |  1 +
 2 files changed, 18 insertions(+)

diff --git a/cores/arduino/wiring.c b/cores/arduino/wiring.c
index 157d1d2..2896647 100755
--- a/cores/arduino/wiring.c
+++ b/cores/arduino/wiring.c
@@ -24,11 +24,13 @@
 
 #include "wiring_private.h"
 
+volatile unsigned long timer0_overflow_count = 0;
 volatile unsigned long timer0_clock_cycles = 0;
 volatile unsigned long timer0_millis = 0;
 
 SIGNAL(TIMER0_OVF_vect)
 {
+	timer0_overflow_count++;
 	// timer 0 prescale factor is 64 and the timer overflows at 256
 	timer0_clock_cycles += 64UL * 256UL;
 	while (timer0_clock_cycles > clockCyclesPerMicrosecond() * 1000UL) {
@@ -51,6 +53,21 @@ unsigned long millis()
 	return m;
 }
 
+unsigned long micros() {
+	unsigned long m, t;
+	uint8_t oldSREG = SREG;
+	
+	cli();	
+	t = TCNT0;
+	if ((TIFR0 & _BV(TOV0)) && (t == 0))
+		t = 256;
+
+	m = timer0_overflow_count;
+	SREG = oldSREG;
+	
+	return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());
+}
+
 void delay(unsigned long ms)
 {
 	unsigned long start = millis();
diff --git a/cores/arduino/wiring.h b/cores/arduino/wiring.h
index 46d5334..9600a0f 100755
--- a/cores/arduino/wiring.h
+++ b/cores/arduino/wiring.h
@@ -113,6 +113,7 @@ int serialRead(void);
 void serialFlush(void);
 
 unsigned long millis(void);
+unsigned long micros(void);
 void delay(unsigned long);
 void delayMicroseconds(unsigned int us);
 unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout);