77 lines
1.7 KiB
ArmAsm
77 lines
1.7 KiB
ArmAsm
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#include <avr/io.h>
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#define VERT_PORT PORTB
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#define HORIZ_DDR DDRD
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#define SHADE_CYCLES 16
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.section .data
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iteration:
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.byte 0
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.section .text
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.extern cmd
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.extern screen
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.global TWI_vect
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.global TIMER2_COMP_vect
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; TIMER2 interrupt routine.
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; Registers:
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; r0 SREG
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; r18 Iteration number
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; Vertical position (VERT_PORT)
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; Busy loop
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; Image data (HORIZ_DDR)
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; X *screen
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TIMER2_COMP_vect:
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push r0
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push r18
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push XL
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push XH
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in r0, _SFR_IO_ADDR(SREG) ; Save SREG.
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ldi XL, lo8(screen) ; Load start address of the screen into X.
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ldi XH, hi8(screen)
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lds r18, iteration
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add XL, r18 ; add as offset to X.
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adc XH, r1
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inc r18 ; Increase iteration.
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andi r18, 0x0f ; Clip iteration into range 0:7.
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sts iteration, r18
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in r18, _SFR_IO_ADDR(VERT_PORT) ; Load vertical position into r18.
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lsl r18 ; Switch to the next vertical position.
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brne set_row
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ldi r18, 1 ; Reset to 1 if 0.
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clt ; Clear T flag in SREG.
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set_row:
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out _SFR_IO_ADDR(HORIZ_DDR), r1 ; Zero out row.
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out _SFR_IO_ADDR(VERT_PORT), r18 ; Push next position into io register.
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load_img:
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ld r18, X+ ; Load image data into r18
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out _SFR_IO_ADDR(HORIZ_DDR), r18 ; Push image data into row.
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brts exit
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set ; Set T flag in SREG to exit after the second iteration.
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adiw X, 7
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ldi r18, SHADE_CYCLES
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wait: ; Busy loop.
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dec r18
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brne wait
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rjmp load_img
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exit:
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out _SFR_IO_ADDR(SREG), r0 ; Restore SREG.
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pop XH
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pop XL
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pop r18
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pop r0
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reti
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