; Tests subroutine calls via stack
;
; This subroutine call is not implemented via the RCALL command
; but by using the processor stack. The sequence is: first the
; return adress is pushed onto the stack, then the adress of
; the subroutine to be called. The jump to the subroutine and
; back to the main program is done by executing the RET-
; command (popping the adress from the stack and jump to
; this adress).
; This adressing mode is a very unusual opportunity, e.g. to write
; multiple jump adresses to a table and calculate the target adress.
; It is not meant for the beginner.
;
.NOLIST
.INCLUDE "C:\avrtools\appnotes\8515def.inc"
.LIST
;
.DEF	mpr=R16 ; As always, a multi-purpose working register
;
; Reset-/Interrupt-Vector table
;
	rjmp	main
;
main:
	ldi	mpr,HIGH(RAMEND) ; Stack setup
	out	SPH,mpr
	ldi	mpr,LOW(RAMEND)
	out	SPL,mpr
	ldi	mpr,LOW(retret) ; Push return adress onto stack
	push	mpr
	ldi	mpr,HIGH(retret)
	push	mpr
	ldi	mpr,LOW(testup) ; Push subroutine adress onto stack
	push	mpr
	ldi	mpr,HIGH(testup)
	push	mpr
	ret ; Jump to subroutine
;
; The return routine switches all lamps on to signal correct execution
;
retret:
	ldi	mpr,0x00 ; Switch all LEDs on, if correct
	out	PORTB,mpr
loop:
	rjmp	loop ; stop execution
;
;
; Test subroutine to be jumped to
;
testup:
	ldi	mpr,0xFF ; All lamp drivers tov output
	out	DDRB,mpr
	ret ; Jump back to call adress on the stack