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; $Id: test_toie0.asm,v 1.2 2003/11/29 09:43:14 troth Exp $
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;;; Test the Timer/Counter 0 overflow interrupt functionality.
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;;; This test will stop the counter by setting the clock select
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;;; value in TCCR0 to 0 (stop).
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.equ zero, 17 ; r17 preset with 0x00
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.equ ones, 18 ; r18 preset with 0xff
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.equ disp, 19 ; r19 is output display
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;;; Interrupt Jump Table
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rjmp TIMER_OVF ; timer0 ovf
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;; Toggle the leds on Port B so we know that the interrupt
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;; occured and was handled.
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out PORTB, disp ; set the leds
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dec disp ; decrement the display counter
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;; if disp has counted down to 0, stop the counter via TCCR,
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;; but leave the interrupt enabled
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brne OVF_RETURN ; skip to reti if disp is not zero
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out TCCR0, r20 ; set clock select to 0x00 (stop)
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reti ; return from interrupt
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;; init stack pointer to 0x025f (the last byte of int sram)
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ldi r16, lo8(RAMEND); low byte of end of int sram
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ldi r16, hi8(RAMEND); high byte of end of int sram
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;; preload zero and ones
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;; init portb for output
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;; Set the clock select for Timer0 to CK/256
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ldi r20, 0x04 ; CS[2,1,0] = [1,0,0]
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out TCCR0, r20 ; write to Timer/Counter Control Register 0
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;; Enable the Timer0 Overflow interrupt
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out TIMSK, r20 ; set toie0 bit of timsk I/O register
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sei ; set global interrupt enable (in sreg)
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;; Loop until r20 is zero
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test_asm/test_8515/test_toie0.asm
