143 lines
3.0 KiB
NASM
143 lines
3.0 KiB
NASM
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; .setcpu "65C02"
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.include "./macro.inc"
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; okay so rn i wanna set up a very basic system init, and write a few subroutines to draw characters at x,y coordinates
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n = $01 ; temporary storage for data stack operations
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key_row = $200 ; used for character lookup when key pressed
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key_col = $201
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cursor = $202
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char_buffer = $300 ; 256 byte character buffer
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kb_row = $4400 ; keyboard hardware register, there are 5 more but i can just increment from here
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kb_row_cache = $203 ; cache
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.org $8000
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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 #$20
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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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keyboard:
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ldy #5
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.loop: ; loop through each row
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lda kb_row, y
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bne key_down; if row has key pressed, go to key_down subroutine
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dey
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bne .loop
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rts
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key_down: ; a is loaded with the row byte
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sty key_row ; store character row
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inc cursor
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pha
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phy
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ldy #0
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.find_col: ; test each row bit, store column if key pressed
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lsr ; test bit 7
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bcs store_col ; if unset, don't go store character columnb
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.skip:
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iny
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cpy #8
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bne .find_col ; loop until we've checked each bit
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do_something_w_key: ; we've stored the character position, now let's
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lda keymap, y
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ldy cursor
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sta $6000, y
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ply
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pla
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rts
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keymap_0:
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.byte "?outrew?"
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keymap_1:
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.byte "?piygsq?"
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keymap_2:
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.byte "a??khvd?"
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keymap_3:
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.byte "42ljbfz?"
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keymap_4:
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.byte "31?mncx?"
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keymap_5:
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.byte "????? m"
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draw:
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push_coords #0, #0
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push_char #$00
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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 keyboard
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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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