/
6502.html
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/
6502.html
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<!DOCTYPE html>
<!--
****************************************************************************
******************************************************************************
** **
** Copyright (c) 2023 by Andrea Griffini **
** **
** Permission is hereby granted, free of charge, to any person obtaining **
** a copy of this software and associated documentation files (the **
** "Software"), to deal in the Software without restriction, including **
** without limitation the rights to use, copy, modify, merge, publish, **
** distribute, sublicense, and/or sell copies of the Software, and to **
** permit persons to whom the Software is furnished to do so, subject to **
** the following conditions: **
** **
** The above copyright notice and this permission notice shall be **
** included in all copies or substantial portions of the Software. **
** **
** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, **
** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF **
** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND **
** NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE **
** LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION **
** OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION **
** WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. **
** **
******************************************************************************
****************************************************************************
-->
<html>
<head>
<title>6502 emulator</title>
<style>
#canvas {
image-rendering: pixelated;
background: #000;
}
#source {
overflow: auto;
white-space: pre;
font-family: monospace;
height: 500px;
width: 500px;
}
</style>
</head>
<body>
<table border=0>
<tr><td valign="top">
Virtual graphic screen<br/>
<canvas id="canvas"></canvas>
</td><td valign="top">
<select id="examples" onchange="loadexample()">
<option value="">Select a demo program</option>
<option value="demo1.asm">Graphic demo</option>
<option value="demo2.asm">Self-modifying code</option>
<option value="demo0.asm">Special locations only</option>
</select><br/>
<textarea id="source">...put your code...</textarea><br/>
<input type=button value="Run" onclick="doit()">
</td></tr></table>
<script src="6502.js"></script>
<script>
function http(verb, url, data, onSuccess, onFail)
{
let req = new XMLHttpRequest();
if (onSuccess) {
req.onreadystatechange = function() {
if (req.readyState === 4) {
if (req.status === 200) {
onSuccess(req.responseText, url, req);
} else {
if (onFail)
onFail(url, req.status);
else
throw new String("Ajax request error (url=" +
url +
", status=" +
req.status + ")");
}
}
}
}
req.open(verb, url, !!onSuccess);
req.send(data);
return onSuccess ? req : req.responseText;
}
function loadexample()
{
let example_name = document.getElementById("examples").value;
http("GET", example_name, "", function(x){
document.getElementById("source").value = x;
});
}
// Virtual screen interface /////////////////////////////////////////////////////
let canvas = document.getElementById("canvas");
canvas.width = canvas.height = 256;
canvas.style.width = (512 / window.devicePixelRatio) + "px";
canvas.style.height = (512 / window.devicePixelRatio) + "px";
let ctx = canvas.getContext("2d");
let data = ctx.getImageData(0, 0, 256, 256);
let bytes = data.data;
let current_palette = [];
let current_palette_index = 0;
let current_palette_comp = 0;
let current_address = 0;
for (let i=0; i<6*6*6; i++) {
let b = i%6, g = (i/6|0)%6, r = i/36|0;
current_palette.push([r*51, g*51, b*51]);
}
for (let i=0; i<40; i++) {
current_palette.push([Math.floor(i*255/39 + 0.5),
Math.floor(i*255/39 + 0.5),
Math.floor(i*255/39 + 0.5)]);
}
for (let i=0; i<256*256; i++) {
bytes[i*4+3] = 255;
}
function set_palette(x) { current_palette_index = x; current_palette_comp = 0; }
function write_color(x) {
current_palette[current_palette_index][current_palette_comp] = x;
if (++current_palette_comp == 3) {
current_palette_comp = 0;
current_palette_index = (current_palette_index + 1) & 255;
}
}
function set_row(x) { current_address = x*256*4 + (current_address & (255*4)); }
function set_col(x) { current_address = x*4 + (current_address & (255*256*4)); }
function write_pixel(x) {
let c = current_palette[x];
bytes[current_address] = c[0];
bytes[current_address+1] = c[1];
bytes[current_address+2] = c[2];
current_address = (current_address + 4) & (256*256*4-1);
}
// Random numbers and time tracking
let ctime = 0;
function random() { return (Math.random() * 256) & 255; }
function clock0() { ctime = (new Date).getTime(); return ctime&255; }
function clock1() { return (ctime >> 8) & 255; }
function clock2() { return (ctime >> 16) & 255; }
function clock3() { return (ctime >> 24) & 255; }
// Mouse support
let current_mx=0, current_my=0, current_mb=255, cmx=0, cmy=0;
canvas.onmousemove = (event) => {
let r = canvas.getBoundingClientRect();
cmx = (event.clientX - r.left) * 256 / r.width | 0;
cmy = (event.clientY - r.top) * 256 / r.height | 0;
current_mb = event.buttons;
};
canvas.onmousein = canvas.onmousemove;
canvas.onmousedown = canvas.onmousemove;
canvas.onmouseup = canvas.onmousemove;
canvas.onmouseout = (event) => {
cmx = 0; cmy = 0; current_mb = 255;
}
canvas.oncontextmenu = (event) => {
event.preventDefault();
event.stopPropagation();
return false;
};
function mouseb() { current_mx = cmx; current_my = cmy; return current_mb; }
function mousex() { return current_mx; }
function mousey() { return current_my; }
// Note: special read/write only works for LDA/STA absolute
special_write[0xFF00] = set_palette;
special_write[0xFF01] = write_color;
special_write[0xFF02] = set_row;
special_write[0xFF03] = set_col;
special_write[0xFF04] = write_pixel;
special_read[0xFF80] = random;
special_read[0xFF81] = clock0;
special_read[0xFF82] = clock1;
special_read[0xFF83] = clock2;
special_read[0xFF84] = clock3;
special_read[0xFF85] = mouseb;
special_read[0xFF86] = mousex;
special_read[0xFF87] = mousey;
function doit()
{
try
{
assemble(document.getElementById("source").value);
}
catch(err)
{
alert(err);
return;
}
setTimeout(run, 0);
}
document.getElementById("source").value = `;
; Special locations
; (they work with LDA/STA abs only!)
;
set_palette = $FF00 ; W: sets current index
write_color = $FF01 ; W++: R, G or B
set_row = $FF02 ; W: pixel row
set_col = $FF03 ; W: pixel col
write_pixel = $FF04 ; W++: writes a pixel
random = $FF80 ; R: a random byte
clock0 = $FF81 ; R: updates clock and returns low byte
clock1 = $FF82 ; R: returns second byte of clock
clock2 = $FF83 ; R: returns third byte of clock
clock3 = $FF84 ; R: returns fourth byte of clock
mouse_b = $FF85 ; R: mouse buttons (bits 0/1/2) or 255 if outside
mouse_x = $FF86 ; R: mouse x position (0 if outside)
mouse_y = $FF87 ; R: mouse y position (0 if outside)
;
; Execution begins at "start" and stops when
; program counter becomes $0000
;
.org $0200
.db $0c, $02, $35, $02, $6a, $02, $a1, $02, $e0, $02, $5b, $03, $ff, $00, $6f, $05
.db $1a, $07, $19, $07, $19, $07, $19, $07, $1a, $05, $1c, $03, $1c, $05, $1a, $07
.db $18, $09, $19, $05, $1b, $05, $1a, $07, $19, $07, $18, $09, $17, $09, $17, $09
.db $18, $07, $17, $0b, $4a, $ff, $00, $2a, $03, $01, $06, $01, $03, $12, $03, $01
.db $06, $01, $03, $12, $0e, $12, $0e, $12, $0e, $12, $0e, $12, $0e, $13, $0c, $16
.db $08, $18, $08, $17, $0a, $16, $0a, $16, $0a, $16, $0a, $15, $0c, $14, $0c, $14
.db $0c, $14, $0c, $13, $0e, $12, $0e, $12, $0e, $49, $b0, $01, $1f, $02, $1e, $03
.db $1c, $05, $1a, $07, $18, $09, $16, $0b, $14, $0c, $13, $0d, $12, $0e, $11, $0f
.db $12, $06, $01, $07, $13, $01, $04, $08, $16, $0a, $14, $0c, $13, $0c, $14, $0c
.db $13, $0d, $13, $0d, $13, $0d, $14, $0c, $14, $0d, $12, $0e, $11, $10, $10, $10
.db $48, $4f, $02, $1e, $02, $1d, $04, $1b, $06, $19, $07, $19, $06, $02, $01, $16
.db $06, $02, $02, $16, $05, $02, $03, $16, $0a, $17, $08, $18, $08, $1a, $04, $1b
.db $06, $18, $0a, $15, $0c, $17, $06, $19, $08, $18, $08, $18, $08, $17, $0a, $16
.db $0a, $16, $0a, $15, $0c, $14, $0c, $14, $0c, $14, $0c, $15, $0a, $13, $10, $48
.db $cc, $02, $04, $02, $17, $04, $02, $04, $16, $04, $02, $04, $12, $02, $03, $02
.db $04, $02, $03, $02, $0d, $04, $03, $01, $04, $01, $03, $04, $0c, $04, $03, $02
.db $02, $02, $03, $04, $0d, $02, $04, $06, $04, $02, $0f, $02, $03, $06, $03, $02
.db $10, $04, $01, $06, $01, $04, $0c, $02, $02, $10, $02, $02, $07, $04, $02, $0e
.db $02, $04, $06, $04, $02, $0e, $02, $04, $07, $02, $01, $12, $01, $02, $0a, $14
.db $0c, $14, $0d, $12, $0e, $12, $0e, $08, $02, $08, $0f, $01, $0e, $01, $10, $06
.db $01, $02, $01, $06, $10, $01, $01, $02, $03, $02, $03, $02, $01, $01, $10, $06
.db $01, $02, $01, $06, $10, $01, $0e, $01, $10, $10, $48, $8f, $02, $1e, $02, $1c
.db $06, $1a, $06, $14, $04, $04, $02, $04, $04, $0c, $09, $01, $02, $01, $09, $09
.db $18, $08, $03, $03, $0c, $03, $03, $07, $03, $05, $0a, $05, $03, $06, $03, $06
.db $08, $06, $03, $06, $03, $02, $01, $01, $01, $02, $06, $02, $01, $01, $01, $02
.db $03, $06, $03, $03, $01, $04, $04, $04, $01, $03, $03, $06, $04, $01, $01, $01
.db $01, $03, $04, $03, $01, $01, $01, $01, $04, $07, $04, $03, $0a, $03, $04, $08
.db $05, $02, $0a, $02, $05, $08, $06, $01, $0a, $01, $06, $09, $08, $01, $04, $01
.db $08, $0b, $08, $04, $08, $0d, $07, $01, $02, $01, $07, $0e, $06, $01, $01, $02
.db $01, $01, $06, $0f, $01, $0e, $01, $10, $06, $01, $02, $01, $06, $10, $01, $01
.db $02, $03, $02, $03, $02, $01, $01, $10, $06, $01, $02, $01, $06, $10, $01, $0e
.db $01, $10, $10, $48
;; Box drawing parameters
x0 = $00
y0 = $01
x1 = $02
y1 = $03
color = $04
;; Animated square position and speed
sqx = $05
sqy = $06
sqdx = $07
sqdy = $08
;; Line drawing
dx = $09
dy = $0A
ix = $0B
iy = $0C
cx = $0D
cy = $0E
m = $0F
;; Counter
count_l = $10
count_h = $11
;; Chess piece definition reader
cpdr_l = $12
cpdr_h = $13
;; Current and old current square on chessboard, secondary square
bcsq = $15
obcsq = $16
bcsq2 = $17
;; Secondary color (foreground) for piece drawing
color2 = $18
;; Draws a line from x0, y0 to x1, y1
drawline:
; dx/ix computation
ldx #$01
lda x1
sec
sbc x0
bcs dlxpos
eor #$FF
sbc #$FE
ldx #$FF
dlxpos:
sta dx
stx ix
; dy/iy computation
ldx #$01
lda y1
sec
sbc y0
bcs dlypos
eor #$FF
sbc #$FE
ldx #$FF
dlypos:
sta dy
stx iy
; m/cx/cy computation
lda dx
cmp dy
bcs dlxm
lda dy
dlxm:
sta m
tay
bne dlsome
rts
dlsome:
lsr a
sta cx
sta cy
; main loop
dlloop:
lda x0
sta set_col
lda y0
sta set_row
lda color
sta write_pixel
; x-inc
lda cx
clc
adc dx
sta cx
bcs dlxi
cmp m
bcc dlnoxi
dlxi:
lda x0
clc
adc ix
sta x0
lda cx
sec
sbc m
sta cx
dlnoxi:
; y-inc
lda cy
clc
adc dy
sta cy
bcs dlyi
cmp m
bcc dlnoyi
dlyi:
lda y0
clc
adc iy
sta y0
lda cy
sec
sbc m
sta cy
dlnoyi:
dey
bne dlloop
rts
;; Fills a box with a solid color
fillbox:
lda y0
sta set_row
lda x0
sta set_col
lda x1
sec
sbc x0
tax
lda color
fbxloop:
sta write_pixel
dex
bne fbxloop
inc y0
lda y0
cmp y1
bne fillbox
rts
;; Sets square coordinates for bouncing animation
set_square:
lda sqx
clc
adc #$08
sta x0
clc
adc #$10
sta x1
lda sqy
clc
adc #$08
sta y0
clc
adc #$10
sta y1
rts
;; Draw chessboard
drawboardsquare:
lda #$00
sta set_palette
sta write_color
sta write_color
sta write_color
lda #$FF
sta write_color
sta write_color
sta write_color
lda #$AA
sta write_color
lda #$BB
sta write_color
lda #$CC
sta write_color
lda #$77
sta write_color
lda #$88
sta write_color
lda #$99
sta write_color
lda #$FF
sta write_color
lda #$00
sta write_color
sta write_color
lda #$C0
sta write_color
lda #$00
sta write_color
sta write_color
lda sqx
asl a
asl a
asl a
asl a
asl a
sta x0
adc #$20
sta x1
lda sqy
asl a
asl a
asl a
asl a
asl a
sta y0
adc #$20
sta y1
lda sqy
asl a
asl a
asl a
adc sqx
cmp bcsq
bne nocurr
lda #$04
bne drawsq
nocurr:
cmp bcsq2
bne nocurr2
lda #$05
bne drawsq
nocurr2:
lda sqx
eor sqy
and #$01
clc
adc #$02
drawsq:
sta color
lda sqy
asl a
asl a
asl a
adc sqx
tax
lda chesspos,x
bne notempty
jmp fillbox
notempty:
tax
and #$08
lsr a
lsr a
lsr a
eor #$01
sta color2
dex
txa
and #$07
asl a
tax
lda $0200,x
sta cpdr_l
lda $0201,x
sta cpdr_h
lda sqx
asl a
asl a
asl a
asl a
asl a
sta x0
lda sqy
asl a
asl a
asl a
asl a
asl a
sta y0
ldy #$FF
lda color2
sta count_h
loadrun:
lda count_h
eor color
eor color2
sta count_h
iny
lda (cpdr_l),y
sta count_l
beq loadrun
proc1:
lda y0
sta set_row
lda x0
sta set_col
lda count_h
sta write_pixel
inc x0
lda x0
cmp x1
bne noy
lda sqx
asl a
asl a
asl a
asl a
asl a
sta x0
inc y0
lda y0
cmp y1
bne noy
rts
noy:
dec count_l
bne proc1
jmp loadrun
drawboard:
lda #$00
sta sqx
sta sqy
drawboard2:
jsr drawboardsquare
inc sqx
lda sqx
eor #$08
bne drawboard2
sta sqx
inc sqy
lda sqy
cmp #$08
bne drawboard2
rts
;; Main program
start:
; clear screen to random
lda #$00
tax
tay
cloop:
lda random
sta write_pixel
dex
bne cloop
dey
bne cloop
; draw 2048 random lines
ldy #$08
ldx #$00
cloop2:
txa
pha
tya
pha
lda random
sta x1
lda random
sta y1
tya
sta color
jsr drawline
pla
tay
pla
tax
dex
bne cloop2
dey
bne cloop2
; Set a green-red bouncing palette
lda #$00
sta set_palette
ldx #$00
ploop1:
txa
sta write_color
eor #$FF
sta write_color
lda #$00
sta write_color
inx
inx
bne ploop1
ploop2:
txa
eor #$FF
sta write_color
eor #$FF
sta write_color
lda #$00
sta write_color
inx
inx
bne ploop2
; Set starting position and speed
lda #$01
sta sqx
sta sqy
sta sqdx
sta sqdy
lda #$00
sta count_l
sta count_h
mainloop:
; Increment square position
lda sqx
clc
adc sqdx
cmp #$DF
bcc xok
lda sqdx
eor #$FF
sta sqdx
inc sqdx
lda sqx
xok:
sta sqx
lda sqy
clc
adc sqdy
cmp #$DD
bcc yok
lda sqdy
eor #$FF
sta sqdy
inc sqdy
lda sqy
yok:
sta sqy
; Draw square
jsr set_square
inc color
jsr fillbox
inc count_l
bne mainloop
inc count_h
bne mainloop
; Chessboard
lda #$FF
sta bcsq
sta obcsq
sta bcsq2
jsr drawboard
mouseloop:
ldx #$00
lda mouse_b
cmp #$FF
beq setsq
tax
lda mouse_y
and #$E0
lsr a
lsr a
sta bcsq
lda mouse_x
lsr a
lsr a
lsr a
lsr a
lsr a
clc
adc bcsq
setsq:
sta bcsq
cpx #$01
bne noclick
tax
waitup:
lda mouse_b
cmp #$01
beq waitup
txa
ldy bcsq2
cpy #$FF
beq nomove
cpx bcsq2
beq updated
lda chesspos,y
sta chesspos,x
lda #$00
sta chesspos,y
updated:
lda #$FF
sta bcsq2
sta bcsq
sta obcsq
jsr drawboard
jmp mouseloop
nomove:
sta bcsq2
noclick:
lda bcsq
cmp obcsq
beq mouseloop
lda obcsq
cmp #$FF
beq no_clear_old
and #$07
sta sqx
lda obcsq
lsr a
lsr a
lsr a
sta sqy
jsr drawboardsquare
no_clear_old:
lda bcsq
sta obcsq
cmp #$FF
beq no_draw_new
and #$07
sta sqx
lda bcsq
lsr a
lsr a
lsr a
sta sqy
jsr drawboardsquare
no_draw_new:
jmp mouseloop
jmp $0000
chesspos:
.db $0a, $0b, $0c, $0d, $0e, $0c, $0b, $0a
.db $09, $09, $09, $09, $09, $09, $09, $09
.db $00, $00, $00, $00, $00, $00, $00, $00
.db $00, $00, $00, $00, $00, $00, $00, $00
.db $00, $00, $00, $00, $00, $00, $00, $00
.db $00, $00, $00, $00, $00, $00, $00, $00
.db $01, $01, $01, $01, $01, $01, $01, $01
.db $02, $03, $04, $05, $06, $04, $03, $02
`;
</script>
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