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#include <avr/io.h>
#include <avr/interrupt.h>
#undef _SFR_IO8
#define _SFR_IO8(x) (x)
#undef _SFR_IO16
#define _SFR_IO16(x) (x)
.global main
main:
ldi r16, 0xff ; all pins output
out DDRB, r16 ; all pins output
ldi r16, 0x01 ; one pin on
out PORTB, r16 ; initial only 1 pin
ldi r16, (1<<UDRIE) ; lets generate a usart data register empty irq
out UCSRB, r16 ; fire hardware irq, but i flag is not set
ldi r17, 0x55
ldi r16, 0x80 ; set I flag
out SREG, r16 ; now the irq is pending
out PORTB, r17 ; if this instruction is executed, we will see 0x55 on portb!
; normaly never execute any of the following instructions, we caught into irq handler
ldi r17, 0x0f; ; if irq will not be executed or comes back
out PORTB, r17 ; we see 0x0f on port b which should not happen
ret ; this will result in going back to ctors_end -> exit
.global USART_UDRE_vect
USART_UDRE_vect:
.global stopsim
stopsim:
rjmp USART_UDRE_vect
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