89 lines
1.7 KiB
NASM
89 lines
1.7 KiB
NASM
; .setcpu "65C02"
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.include "./macro.inc"
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.org $8000
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n = $01 ; temporary storage for data stack operations
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reset:
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sei
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ldx #0; initialize data stack pointer
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initdisplay:
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lda #0
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ldy #0
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cleardisplay:
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sta $6000,y
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sta $6100,y
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sta $6200,y
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sta $6300,y
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sta $6400,y
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sta $6500,y
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sta $6600,y
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sta $6700,y ; this goes slightly over but it's fine
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iny
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bne cleardisplay
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cli
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main:
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jsr draw
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jmp main
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draw:
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push_coords #0, #0
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push_char #$af
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jsr draw_char
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rts
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draw_char: ; draw a character c at (x, y) (n1: x n2: y n3: c -- )
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lda 0, x ; load a with character to draw
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pop ; and pop it off the stack
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jsr get_char_address ; calculate where to put the character in memory
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sta (0, x) ; store a at the address pointed to on the stack
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rts
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get_char_address: ; gets vram address for a character at (x, y),
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; (n1: x n2: y -- n: $6000 + x + (64 * y))
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;jsr push_lit ; push 64 onto stack, low byte first
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;.byte 64
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;.byte 0
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pha
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lda #64
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push ; doing this instead until `push_lit` is fixed
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sta 0, x
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stz 1, x
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jsr mult ; multiply 64 with y (n2)
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jsr plus ; add result with x (n1)
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;jsr push_lit ; push vram address onto the stack
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;.byte $00
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;.byte $60
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lda #$60
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push
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sta 1, x
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stz 0, x
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jsr plus ; add vram start address to result
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pla
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rts
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fill: ; fills an area from (x1, y1) to (x2, y2) will character c, (n1: c n2: x1 n3: y1 n4: x2 n5: y2 -- )
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jsr get_char_address
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isr: ; interrupt service routine
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pha
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phx
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phy
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; jsr irq
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ply
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plx
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pla
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rti
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.include "math.inc"
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.org $fffc
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.word reset
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.word isr
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