// alter drehimpulsgebercode, aus marcus-thermometer
void buttonpoll(){  // runs with 1.2kHz
	uint8_t l,r,t,flanks,dir;
	l=BUTTPIN & _BV(BUTTLPIN);
	r=BUTTPIN & _BV(BUTTRPIN);
	t=BUTTPIN & _BV(BUTTTPIN);

	// debounce code
	if (t != butttold && !butttbounce ) {
		butttold = t;
		butttbounce = BUTT_BOUNCE;
		if (t == 0) { // active low
			buttonevent |= BUTTEV_PUSH;
		}
	}

	flanks=0;
	dir=0;
	if (l != buttlold) {
		flanks += 1;
	}
	if (r != buttrold) {
		flanks += 1;
		dir = 1;
	}
	if (flanks == 1){ // we need to have exactly one flank, 0 flanks are no
					  // change, and 2 flanks are too fast (error)
		if (l) {
			dir ^= 1;
		}
		if (r) {
			dir ^= 1;
		}
		if ((r && l) || (!r && !l)) {
			buttoninc += dir ? -1 : 1;
		}
	}

	buttlold = l;
	buttrold = r;


	if(butttbounce){
		butttbounce -= 1;
	}

}