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|
;
; $Id: test_toie0.asm,v 1.2 2003/11/29 09:43:14 troth Exp $
;
;;; Test the Timer/Counter 0 overflow interrupt functionality.
;;; This test will stop the counter by setting the clock select
;;; value in TCCR0 to 0 (stop).
.include "8515def.inc"
.equ zero, 17 ; r17 preset with 0x00
.equ ones, 18 ; r18 preset with 0xff
.equ disp, 19 ; r19 is output display
;;; Interrupt Jump Table
rjmp MAIN ; reset
nop ; int0
nop ; int1
nop ; timer1 capt
nop ; timer1 compa
nop ; timer1 compb
nop ; timer1 ovf
rjmp TIMER_OVF ; timer0 ovf
nop ; spi, stc
nop ; uart, rx
nop ; uart, udre
nop ; uart, tx
nop ; ana_comp
TIMER_OVF:
;; Toggle the leds on Port B so we know that the interrupt
;; occured and was handled.
out PORTB, disp ; set the leds
dec disp ; decrement the display counter
;; if disp has counted down to 0, stop the counter via TCCR,
;; but leave the interrupt enabled
brne OVF_RETURN ; skip to reti if disp is not zero
ldi r20, 0x00
out TCCR0, r20 ; set clock select to 0x00 (stop)
OVF_RETURN:
reti ; return from interrupt
MAIN:
;; init stack pointer to 0x025f (the last byte of int sram)
ldi r16, lo8(RAMEND); low byte of end of int sram
out SPL, r16
ldi r16, hi8(RAMEND); high byte of end of int sram
out SPH, r16
;; preload zero and ones
ldi zero, 0x00
ldi ones, 0xff
ldi disp, 0xff
;; init portb for output
out DDRB, ones
out PORTB, disp
;; Set the clock select for Timer0 to CK/256
ldi r20, 0x04 ; CS[2,1,0] = [1,0,0]
out TCCR0, r20 ; write to Timer/Counter Control Register 0
;; Enable the Timer0 Overflow interrupt
ldi r20, 1<<TOIE0
out TIMSK, r20 ; set toie0 bit of timsk I/O register
sei ; set global interrupt enable (in sreg)
IDLE_LOOP:
;; Loop until r20 is zero
tst r20
brne IDLE_LOOP
DONE:
rjmp DONE
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