int min_mem=32000;
 int free_mem=0;
 ISR(TIMER1_COMPA_vect) {
 cli();
   extern int __heap_start, *__brkval;
   int m = (int) &m - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
   if (m < min_mem) min_mem=m;
   free_mem=m;
 sei();
 } 
 
 int main(void) {
 	init();
 	cli();
 	TCCR1A = 0;
 	TCCR1B = 0;
 	TCNT1  = 0;
 	OCR1A = 1000;
 	TCCR1B |= (1 << WGM12);
 	TCCR1B |= (1 << CS11);
 	TIMSK1 |= (1 << OCIE1A); 
 	sei();
 	
 	while (1) {
 		do_stuff();
 		delay(100);
 		Serial.print("mem: ");
 		Serial.print(free_mem,DEC);
 		Serial.print(" - lowest: ");
 		Serial.println(min_mem,DEC);
 	}
 }