intex1.c

startup code has configured Timer0

// Program 1 from the Using Interrupts example.
// Assumes the startup code has configured Timer0
// for a 25mSec interrupt.
// Ron Kreymborg

#include <avrstdio.h>

void main(void);
void CheckInt(void);

extern char I_Time;

main(void) {
	int n;
	
	outp(DDRB,0xff);					// all are outputs
	outp(PORTB, 0xff);				// and all are high
	n = 0;								// zero counter
	
	while (1) {							// do forever
		CheckInt();						// wait for interrupt
		if (++n == 40) {				// if 40 have occured
			outp(PORTB, 0x7f);		// bit 7 of PORTB low
			CheckInt();					// keep low for 25mSec
			outp(PORTB, 0xff);		// bit 7 high again
			n = 0;						// ready for next cycle
			}
		}		
}


void CheckInt() {
	while (I_Time == 0)				// wait
		;
	I_Time = 0;						// must reset flag
}