george-emu/roms/keyboard_sys.asm

; .setcpu "65C02"
    .include "./macro.inc"

    .org $8000

n = $01 ; temporary storage for data stack operations

temp = $20 ; scratchpad page
str_ptr = $30

cursor = $300
cursor_x = cursor
cursor_y = cursor + 1

char_buf = $302
char_buf_index = char_buf + 8

reset:
    sei
    ldx #0; initialize data stack pointer

init:
    lda #$31
    sta str_ptr
    lda #$80
    sta str_ptr + 1

    jsr clear
    lda #0
    sta cursor_x
    lda #0
    sta cursor_y
    cli

main:
    jsr print
    jmp main

newline: ; sets cursor to start of next line
    stz cursor_x
    lda cursor_y
    cmp #28
    bne .end
    stz cursor_y
    rts
    .end:
        inc cursor_y
        rts

text:
    .asciiz "hello <3"

; increments the cursor line by line, looping to (0, 0) after (63, 28)

inc_cursor:
    lda cursor_x
    cmp #63
    beq .newline
    inc cursor_x 
    rts
    .newline:
        lda cursor_y
        cmp #28
        beq .newscreen
        stz cursor_x
        inc cursor_y
        rts
    .newscreen:
        stz cursor_y
        stz cursor_x
        rts

; zeroes out the display, resets cursor to 0,0

clear: 
    lda #0
    ldy #0

   .loop:
        sta $6000,y
        sta $6100,y
        sta $6200,y
        sta $6300,y
        sta $6400,y
        sta $6500,y
        sta $6600,y
        sta $6700,y ; this goes slightly over but it's fine
        iny
        bne .loop
    stz cursor
    stz cursor + 1
    rts


; prints string from cursor position, stopping at end of string or at 256 chars, whichever comes first
; $6000 + (64*Y) + X
; THIS WILL WRITE OUT OF BOUNDS IF THE CURSOR IS OUT OF BOUNDS/STRING IS TOO LONG

; TODO: figure out a simple way of writing arbitrary length strings
; and 

print: 
   jsr cursor_addr
   ldy #0
   ; y_overflow = temp + 5
   .loop:
       lda (str_ptr), y
       beq .end
       sta (temp), y
       iny
       bra .loop
   .end:
   rts


; calculates real vram address from cursor (x, y)

cursor_addr:
    stz temp
    stz temp + 1
    lda cursor_y
    beq .add_x ; if y's zero just add x
    .y_mult:
        ; multiply by 64
        clc
        asl
        rol temp + 1 
        asl
        rol temp + 1 
        asl  
        rol temp + 1 
        asl  
        rol temp + 1 
        asl  
        rol temp + 1 
        asl  
        rol temp + 1 
        sta temp
    .add_x:
        clc
        lda cursor_x
        adc temp
        sta temp 
        lda #0
        adc temp + 1
        sta temp + 1
        clc

        lda #$60
        adc temp + 1
        sta temp + 1
    rts



; print_text:
;     lda text,y
;     beq .end
;     sta $6000, y
;     iny
;     bra print_text
;     .end:
;         ldy #0
;         rts

; draw_char: ; draw a character c at (x, y) (n1: x n2: y n3: c -- )
;     lda 0, x ; load a with character to draw
;     pop ; and pop it off the stack
;     jsr get_char_address ; calculate where to put the character in memory
;     sta (0, x) ; store a at the address pointed to on the stack
;     rts

; get_char_address:   ; gets vram address for a character at (x, y),
;                     ; (n1: x n2: y -- n: $6000 + x + (64 * y))
;     ;jsr push_lit ; push 64 onto stack, low byte first
;     ;.byte 64
;     ;.byte 0
;     pha
;     lda #64
;     push ; doing this instead until `push_lit` is fixed
;     sta 0, x
;     stz 1, x
;     jsr mult ; multiply 64 with y (n2)
;     jsr plus ; add result with x (n1)

;     ;jsr push_lit ; push vram address onto the stack
;     ;.byte $00
;     ;.byte $60
;     lda #$60
;     push
;     sta 1, x
;     stz 0, x
;     jsr plus ; add vram start address to result

;     pla
;     rts

; fill: ; fills an area from (x1, y1) to (x2, y2) will character c, (n1: c n2: x1 n3: y1 n4: x2 n5: y2 -- )
;     jsr get_char_address

isr: ; interrupt service routine
    pha
    phx
    phy
    ; jsr irq
    ply
    plx
    pla
    rti

    .include "math.inc"

    .org $fffc
    .word reset
    .word isr