Adding micros() function.

build/shared/lib/keywords.txt

@@ -149,6 +149,7 @@ digitalWrite	KEYWORD2	DigitalWrite
 digitalRead	KEYWORD2	DigitalRead
 interrupts	KEYWORD2
 millis	KEYWORD2	Millis
+micros	KEYWORD2	Micros
 noInterrupts	KEYWORD2
 pinMode	KEYWORD2	PinMode
 pulseIn	KEYWORD2	PulseIn

hardware/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();

hardware/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);