6502
Introduction
Wanting to start sizecoding on a 6502 platform in this day and age can be tough.
So here is a bit of help to get you started:
The 6502 processor
The 6502 processor can be seen as the 8bit micro ARM chip. It has only has 3 registers (Accumilator, IX and IY registers) and only a handful of instructions to work with.
Zero page
When using the 6502 for sizecoding, you'll mostly be working from zeropage
Atari 8bit family
The Atari XE/XL systems consists of the 6502 with custom hardware for graphics and sound.
Setting up
Setting up your development platform for the Atari 8bit systems is quite easy, first get the following tools:
- Assembler: MADS Assembler - This assembler has nice macros for creating Binaries and SNA snapshot files out of the box. You can download it at https://mads.atari8.info/
- Emulator(s): I Found Altirra to work best for my usecase. Make sure to use the original Rev2 rom for best compatibility.
Special Memory Adresses
- FRAMECOUNTER_HIGH = 19
- FRAMECOUNTER_LOW = 20
Video display
Video display on the Atari 8bit systems use the TIA chip, it has the following video modes:
To be added soon.
Getting something on screen
To be added soon.
SDMCTL = $022f
HPOSP0 = $d000
SIZEP0 = $d008
GRAFP0 = $d00d
COLPM0 = $d012
FRAMECOUNTER_HIGH = 19
FRAMECOUNTER = 20
WSYNC = $d40a
VCOUNT = $d40b
sinewave = $0600 ; to $06ff
org $80
main
; disable all graphics/colors
ldx #0
stx SDMCTL
ldy #$7f
sty SIZEP0 ; size p0=127
ldx #0
ldy #$3f
make_sine:
value_lo
lda #0
clc
delta_lo
adc #0
sta value_lo+1
value_hi
lda #0
delta_hi
adc #0
sta value_hi+1
sta sinewave+$c0,x
sta sinewave+$80,y
eor #$7f
sta sinewave+$40,x
sta sinewave+$00,y
lda delta_lo+1
adc #8
sta delta_lo+1
bcc nothing
inc delta_hi+1
nothing
inx
dey
bpl make_sine
updateloop:
; vblank
lda VCOUNT
bne updateloop
; clear graphics
sta HPOSP0
sta GRAFP0
ldy #0
lda #47
sta COLPM0
yloop:
tya ; graphics shape = y
sta WSYNC
sta GRAFP0
; a = sin(frame+y)+48
tya
adc FRAMECOUNTER
tax
lda sinewave,x
adc #48
sta HPOSP0
iny
bne yloop
jmp updateloop
run main
Sound
The Atari 8bit systems use the Pokey chip to generate sound. To be added soon.
Make some noise
To be added soon.
Additional Resources
Sizecoding resource for the Atari 8bit are sparse
- Fready's github (link to be added)
Atari Lynx
The Atari Lynx consists of the 6502 with custom hardware for graphics and sound.
Setting up
Setting up your development platform for the Atari Lynx:
- Assembler: -
- Emulator(s): -
Video display
To be added soon.
Getting something on screen
To be added soon.
Sound
To be added soon.
Make some noise
To be added soon.
Additional Resources
Sizecoding resource for the Atari Lynx are sparse
- 42Bastian's website (link to be added)
Commodore 64
The Commodore systems consists of the 6502 with custom hardware for graphics and sound.
Setting up
Setting up your development platform for the Commodore systems is quite easy, first get the following tools:
- Assembler: To be added
- Emulator(s): VICE is the way to go
Autoboot
*=$0326
.word start
.byte $ed,$f6
start
; rest of code
Will give you autoboot and more space directly. (though writing through to $0400 will load it onto the screen unless you move the pointers)
Video display
Video display on the Commodore, it has the following video modes:
To be added soon.
Getting something on screen
To be added soon.
Sound
The Commodore 64 uses the famous SID chip to generate sound. To be added soon.
Make some noise
To be added soon.
Additional Resources
- links to be added
Apple II
The Apple II is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak.
Setting up
- ACME 6502 cross-assembler(https://sourceforge.net/projects/acme-crossass/)
- Apple Commander (http://applecommander.sourceforge.net) for batch compilation
- AppleWin emulator (https://github.com/AppleWin/AppleWin/releases). Supports Mockingboard card(AY-8910+speech synthesier), HDD, Z80 card(for CP/M), mouse etc.
- CiderPress(https://a2ciderpress.com)
Compilation can be done as follows (master.dsk can be found with applewin)
acme hl.asm
java -jar AppleCommander-1.3.5.jar -d master.dsk hl
java -jar AppleCommander-1.3.5.jar -p master.dsk hl B 24576 < hl.bin
Memory Map
0-255 $0-$FF ZERO-PAGE SYSTEM STORAGE
256-511 $100-$1FF SYSTEM STACK
512-767 $200-$2FF KEYBOARD CHARACTER BUFFER
768-975 $300-$3CF OFTEN AVAILABLE AS FREE SPACE FOR USER PROGRAMS
976-1023 $3D0-3FF SYSTEM VECTORS
1024-2047 $400-$7FF TEXT AND LO-RES GRAPHICS PAGE 1 <--- !!!
2048-LOMEM $800-LOMEM PROGRAM STORAGE
2048-3071 $800-$BFF TEXT AND LO-RES GRAPHICS PAGE 2 OR FREE SPACE
3072-8191 $C00-$1FFF FREE SPACE UNLESS RAM APPLESOFT IS IN USE
8192-16383 $2000-$3FFF HI-RES PAGE 1 OR FREE SPACE <--- !!!
16384-24575 $4000-$5FFF HI-RES PAGE 2 OR FREE SPACE
24576-38999 $6000-$95FF FREE SPACE AND STRING STORAGE
38400-49151 $9600-$BFFF DOS
49152-53247 $C000-$CFFF I/O HARDWARE (RESERVED)
53248-57343 $D000-$DFFF APPLESOFT IN LANGUAGE CARD OR ROM
57344-63487 $E000-$F7FF APPLESOFT OR INTEGER BASIC IN LANGUAGE CARD OR ROM
63488-65535 $F800-$FFFF SYSTEM MONITOR
Display
Graphics Modes
- Text Mode 40x24, for Apple IIe available 80x25 - use PR#3 for switch mode, or hardware switch
- LowRes 40x48, 16 colors: https://en.wikipedia.org/wiki/Apple_II_graphics
- Hires mode 280x192,6 colors: https://www.xtof.info/blog/?p=768
https://mrob.com/pub/xapple2/colors.html https://archive.org/details/HiRes_Color_Graphics_on_the_Apple_II_Computer_by_Wozniak
However for sizecoding, you almost never want to do direct-access to graphics for Apple II in size-coding because the Apple II graphics modes are horrible. The only fast way to do things is with large lookup tables. To do hires you need to divide by 7 which as you can imagine is a bit difficult to do compactly on 6502. Double-hires is even crazier on top of that. Deater did manage a color-bar style effect in double-hires in 128B but that was doing some crazy tricks with the firmware BASIC routines, definitely not direct-access.
Lores and Hires can be mixed modes and full-graphics The screen structure is called memory holes(https://retrocomputing.stackexchange.com/questions/2534/what-are-the-screen-holes-in-apple-ii-graphics). The GBASCALC($F847) procedure is used to calculate the address of the horizontal line : IN:reg.A=Y, out : GBASL/GBASH($26/$27)=address. See also https://www.callapple.org/uncategorized/use-of-apple-ii-color-graphics-in-assembly-language/
Getting something on screen
Here is an example of a XOR texture, created by g0blinish
*=$6000
!to "HL.bin", plain ; set output file and format
!cpu 6502 ; set processor type
GBASL = $26
GBASH = $27
SETGR = $FB40 ; setup LoRes
GBASCALC = $F847 ; calc Address
CLRTEXT = $C050 ;display graphics
SETTEXT = $C051 ;display text
CLRMIXED = $C052 ;clear mixed mode- enable full graphics
SETMIXED = $C053 ;enable graphics/text mixed mode
PAGE1 = $C054 ;select text/graphics page1
PAGE2 = $C055 ;select text/graphics page2
CLRHIRES = $C056 ;select Lo-res
SETHIRES = $C057 ;select Hi-res
TMP= $FA
JSR SETGR ;GR
BIT CLRMIXED ; full screen
LDA #0 ; A=0
STA TMP ; POKE $FA,A
YLP ;
LDA TMP ; A=PEEK($FA)
; LSR ; A=A/2
JSR GBASCALC
LDY #0;Y=0
XLP TYA ; A=Y
EOR TMP ; A=A xor PEEK($FA)
and #$0F ; A=A and 15
TAX ; X=A
LDA COLORS,X ;A=PEEK(COLORS+X)
STA(GBASL),Y ; POKE PEEK($26)+256*PEEK($27)+Y,A
INY ; Y=Y+1
CPY #40 ; Y=40?
BNE XLP
INC TMP ; POKE $FA,PEEK($FA)+1
LDA TMP ; A=PEEK($FA)
CMP #24 ; A=24?
BNE YLP
M1 JMP M1 ; replace to RTS
COLORS ;N*17, pixel format is AAAABBBB, AAAA - upper dot, BBBB - lower dot
!byte $00,$11,$22,$33,$44,$55,$66,$77
!byte $88,$99,$AA,$BB,$CC,$DD,$EE,$FF
Sound
Here is an example for using the speaker, based onthe following basic program:
; 50 POKE 768,V: POKE 769,P - 255 * INT (P / 256): POKE 800,1 + P / 256
; 60 CALL 770: RETURN
; 95 FOR K = 1 TO N: READ V(K),P(K): NEXT K
; 100 FOR K = 1 TO N:V = V(K):P = P(K)
; 110 GOSUB 50
;!byte 173,48,192,136,208,5,206,1,3,240,9,202,208,245,174,0,3,76,2,3,206,32,3,208,240,96
*=$6000
!to "HL.bin", plain ; set output file and format
!cpu 6502 ; set processor type
;start
; 95 FOR K = 1 TO N: READ V(K),P(K): NEXT K
; 100 FOR K = 1 TO N:V = V(K):P = P(K)
ini:
lda #70
sta cnt+1
lda #music&255
sta gotbyte+1
lda #music/256
sta gotbyte+2
lop:
;V
jsr gotbyte
sta L300
jsr gotbyte
;P
jsr gotbyte
sta L301
jsr gotbyte
clc
adc #1
sta L320
jsr beep
dec cnt+1
cnt lda #70
bne lop
; 110 GOSUB 50
; 50 POKE 768,V: POKE 769,P - 255 * INT (P / 256): POKE 800,1 + P / 256
; 60 CALL 770: RETURN
jmp ini
gotbyte
lda music
inc gotbyte+1
bne noinch
inc gotbyte+2
noinch
rts
;!byte 173,48,192,136,208,5,206,1,3,240,9,202,208,245,174,0,3,76,2,3,206,32,3,208,240,96
beep:
ldy #1
ldx #1
loc_302:
LDA $C030
loc_305:
DEY
BNE loc_30D
DEC L301
loc_30B:
BEQ loc_316
loc_30D:
DEX
BNE loc_305
LDX L300
JMP loc_302
loc_316:
DEC L320
BNE loc_30B
RTS
L301 !byte 0
L300 !byte 0
L320 !byte 0
music
!word 76,192,85,64,96,64,102,64,114,128,114,64,96,64,102,64,114,64,128,64
!word 114,64,152,64,171,64,152,512,76,192,85,64,96,64,102,64,114,128,114,64
!word 96,64,102,64,114,64,128,64,114,64,152,64,171,64,152,512,85,64,85,64
!word 85,64,96,64,144,128,144,64,128,64,76,128,85,64,96,64,144,128,114,64
!word 96,64,102,128,114,64,128,64,128,128,114,64,128,64,114,512,85,64,85,64
!word 85,64,96,64,144,128,144,64,128,64,76,128,85,64,96,64,144,128,114,64
!word 96,64,102,128,114,64,128,64,128,64,128,128,96,64,85,64,96,64,102,64,114,64,114,64
Additional Resources
- Deater's page on Apple II sizecoding http://www.deater.net/weave/vmwprod/demos/sizecoding.html
- Article on double hi-res http://www.battlestations.zone/2017/04/apple-ii-double-hi-res-from-ground-up.html
- Applesoft Hi-Res Subroutines : http://hackzapple.org/scripts_php/index.php?menu=5&mod=ASM&sub=AAL&sub2=8112&PHPSESSID=f65fabfd0cdbf56b6bdc0ddac25117c6#a2