;; count with interrupt

.symbol
	stop 0
	cnt 20

.code 0
:main
	mv r1 #isr1
	st r1 1000   ;; set up int vector
	mv r27 #2000 ;; set sp
	mv r1 #0
	st r1 cnt    ;; cnt = 0
:loop
;; this is almost empty loop
	ld r1 cnt
	eq r2 r1 #10
	jf r2 loop
	trap stop

;;  the counting routine is split into two
:isr1
	ld r3 cnt	
	add r3 r3 #1
	savr r27
	mv r4 #isr2
	st r4 1000     ;; change interrupt vector
	reti
:isr2
	resr r27
	st r3 cnt
	mv r4 #isr1
	st r4 1000     ;; change int vec
	reti

.end