Difference between revisions of "6502"

Latest revision as of 12:55, 8 April 2024

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 8-bit micro ARM chip. It has only has 3 registers (Accumulator, X and Y registers) and a handful of instructions to work with.

Adressing modes

To be added.

Zero page

When using the 6502 for sizecoding, you'll mostly be working from zeropage

6502 Based Platforms

Atari 8Bit - Atari 8-Bit Family (Atari XL/XE, etc.)
Apple II - Apple II(e)
Commodore 64 - Commodore 64
BBC Micro - Acorn BBC Micro/Master/Electron.
Atari Lynx - Atari Lynx Handheld

Generic 6502 sinus table generator

	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 sintab+$c0,x
			sta sintab+$80,y
			eor #$7f
			sta sintab+$40,x
			sta sintab+$00,y
 
			lda delta_lo+1
			adc #8
			sta delta_lo+1
			bcc nothing
			inc delta_hi+1
nothing
			inx
			dey
			bpl make_sine

General 6502 Resources

6502.org http://www.6502.org/
6502 instruction reference http://www.6502.org/tutorials/6502opcodes.html
6502 books http://retro.hansotten.nl/6502-sbc/
6502 Assembler tutorial https://dwheeler.com/6502/oneelkruns/asm1step.html
Easy 6502 code tester https://skilldrick.github.io/easy6502/
Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate

Difference between revisions of "6502"

Latest revision as of 12:55, 8 April 2024

Contents

Introduction

The 6502 processor

Adressing modes

Zero page

6502 Based Platforms

Generic 6502 sinus table generator

General 6502 Resources

Navigation menu

Personal tools

Namespaces

Variants

Views

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Search

Navigation

Tools

@@ Line 16: / Line 16: @@
 When using the 6502 for sizecoding, you'll mostly be working from zeropage
-=== General 6502 Resources ===
+== 6502 Based Platforms ==
-* 6502.org http://www.6502.org/
+*'''[[Atari 8Bit]]''' - Atari 8-Bit Family (Atari XL/XE, etc.)
-* 6502 instruction reference http://www.6502.org/tutorials/6502opcodes.html
+*'''[[Apple II]]''' - Apple II(e)
-* 6502 books http://retro.hansotten.nl/6502-sbc/
+*'''[[Commodore 64]]''' - Commodore 64
-* 6502 Assembler tutorial https://dwheeler.com/6502/oneelkruns/asm1step.html
+*'''[[BBC Micro]]''' - Acorn BBC Micro/Master/Electron.
-* Easy 6502 code tester https://skilldrick.github.io/easy6502/
+*'''[[Atari Lynx]]''' - Atari Lynx Handheld
-* Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate
-== Atari 8-bit family ==
-The systems in this family are: Atari 400, 800, 5200, 1200XL, 600XL, 800XL, 130XE, 65XE, 800XE and XEGS.<br />
-The Atari 8-bit 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 ANTIC and GTIA chips. Information can be found here:
-* https://en.wikipedia.org/wiki/ANTIC
-* https://www.atariarchives.org/agagd/chapter1.php
-==== Sync with frame  ====
-<syntaxhighlight lang="6502">
-RTCLOK      equ $0012
-      lda RTCLOK+2
-waits
-      cmp RTCLOK+2
-      beq waits
-</syntaxhighlight>
-Or if you don't mind trashing RTCLOK
-<syntaxhighlight lang="6502">
+== Generic 6502 sinus table generator ==
-RTCLOK      equ $0012
+<syntaxhighlight lang="">
-waits
-      lsr RTCLOK+2
-      bcc waits
-</syntaxhighlight>
-Which is two bytes shorter.
-==== Getting something on screen ====
-<syntaxhighlight lang="6502">
-;fill screen with charset,(88,89)=an address
- org $600; free 6th page:600-6ff
- ldy #0
-fl: tya
- sta(88),y
- iny
- bne fl
- jmp *
-</syntaxhighlight>
-To be added soon.
-<syntaxhighlight lang="6502">
-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 #$3f
@@ Line 117: / Line 40: @@
 			sta value_hi+1
-			sta sinewave+$c0,x
+			sta sintab+$c0,x
-			sta sinewave+$80,y
+			sta sintab+$80,y
 			eor #$7f
-			sta sinewave+$40,x
+			sta sintab+$40,x
-			sta sinewave+$00,y
+			sta sintab+$00,y
 			lda delta_lo+1
@@ Line 132: / Line 55: @@
 			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
 </syntaxhighlight>
-=== Sound ===
+=== General 6502 Resources ===
-The Atari 8-bit use the POKEY chip to generate sound.
+* 6502.org http://www.6502.org/
-* https://en.wikipedia.org/wiki/POKEY
+* 6502 instruction reference http://www.6502.org/tutorials/6502opcodes.html
+* 6502 books http://retro.hansotten.nl/6502-sbc/
-==== BASIC ====
+* 6502 Assembler tutorial https://dwheeler.com/6502/oneelkruns/asm1step.html
-<syntaxhighlight lang="6502">
+* Easy 6502 code tester https://skilldrick.github.io/easy6502/
-; from Analog, 1985-09,pp.25-32
+* Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate
-*=$2000
-AUDF1=$D200
-AUDC1=$D201
-AUDCTL=$D208
-SKCTL=$D20F
-.MACRO SOUND ; voice,pitch,dist,vol;,dur
-	lda #%2
-	sta AUDF1+2*%1
-    lda #[[%3 * 16] | %4] ;lda #[[%3 shl 4] or %4]
-    sta AUDC1+2*%1
-.ENDM
- lda #0
- sta AUDCTL
- lda #3
- sta SKCTL
- SOUND 0,121,10,8
- jmp *
-</syntaxhighlight>
-==== Make some noise ====
-To be added soon.
-=== Additional Resources ===
-Sizecoding resource for the Atari 8bit are:
-* Mapping the Atari https://www.atariarchives.org/mapping/
-* Atari 8bit Memory map https://www.atariarchives.org/mapping/memorymap.php
-* Fready's undocumented 6502 opcodes https://github.com/FreddyOffenga/6502
-* Atari OS Rev2 disassembly for MADS assembler https://github.com/ilmenit/A800-OS-XL-Rev2
-* Fready's github https://github.com/FreddyOffenga/
-== 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 ===
-<syntaxhighlight lang="6502">
-*=$0326
-        .word start
-        .byte $ed,$f6
-start
-; rest of code
-</syntaxhighlight>
-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 ===
-* Codebase 64 https://codebase64.org/doku.php?id=base:start
-== 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)
-<syntaxhighlight>
-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
-</syntaxhighlight>
-=== Memory Map ===
-<syntaxhighlight lang="6502">
--255	 $0-$FF     ZERO-PAGE SYSTEM STORAGE
--511      $100-$1FF    SYSTEM STACK
--767      $200-$2FF    KEYBOARD CHARACTER BUFFER
--975      $300-$3CF    OFTEN AVAILABLE AS FREE SPACE FOR USER PROGRAMS
--1023     $3D0-3FF     SYSTEM VECTORS
--2047     $400-$7FF    TEXT AND LO-RES GRAPHICS PAGE 1 <--- !!!
--LOMEM    $800-LOMEM   PROGRAM STORAGE
--3071     $800-$BFF    TEXT AND LO-RES GRAPHICS PAGE 2 OR FREE SPACE
--8191     $C00-$1FFF   FREE SPACE UNLESS RAM APPLESOFT IS IN USE
--16383   $2000-$3FFF   HI-RES PAGE 1 OR FREE SPACE <--- !!!
--24575   $4000-$5FFF   HI-RES PAGE 2 OR FREE SPACE
--38999   $6000-$95FF   FREE SPACE AND STRING STORAGE
--49151   $9600-$BFFF   DOS
--53247   $C000-$CFFF   I/O HARDWARE (RESERVED)
--57343   $D000-$DFFF   APPLESOFT IN LANGUAGE CARD OR ROM
--63487   $E000-$F7FF   APPLESOFT OR INTEGER BASIC IN LANGUAGE CARD OR ROM
--65535   $F800-$FFFF   SYSTEM MONITOR
-</syntaxhighlight>
-=== 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
-<syntaxhighlight lang="6502">
- *=$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
-</syntaxhighlight>
-==== Sound  ====
-Here is an example for using the speaker, based onthe following basic program:
-<syntaxhighlight lang="basic">
-; 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
-</syntaxhighlight>
-<syntaxhighlight lang="6502">
- *=$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
-</syntaxhighlight>
-=== 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
-== 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)