Atari 8Bit - Revision history

Superogue at 22:32, 28 March 2024

2024-03-28T22:32:50Z

Superogue at 22:28, 28 March 2024

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Superogue at 22:22, 28 March 2024

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Superogue at 22:20, 28 March 2024

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Superogue at 22:18, 28 March 2024

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Superogue: Created page with "== Atari 8-bit family == The systems in this family are: Atari 400, 800, 5200, 1200XL, 600XL, 800XL, 130XE, 65XE, 800XE and XEGS.
The Atari 8-bit systems consists of th..."

2022-03-10T13:20:44Z

Created page with "== 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 th..."

New page

== 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">
RTCLOK equ $0012
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
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
</syntaxhighlight>

=== Sound ===
The Atari 8-bit use the POKEY chip to generate sound.
* https://en.wikipedia.org/wiki/POKEY

==== BASIC ====
<syntaxhighlight lang="6502">
; from Analog, 1985-09,pp.25-32
*=$2000
AUDF1=$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/

@@ Line 18: / Line 18: @@
 * https://en.wikipedia.org/wiki/ANTIC
 * https://www.atariarchives.org/agagd/chapter1.php
 ==== Sync with frame  ====

@@ Line 34: / Line 34: @@
 </syntaxhighlight>
-==== Getting something on screen ====
+==== ROM-Routines ====
 <syntaxhighlight lang="6502">
   org $600; free 6th page:600-6ff
   ldy #0
-fl: tya
+fill:
   sta(88),y
   iny
-  bne fl
+  bne fill
   jmp *
 </syntaxhighlight>
-To be added soon.
+==== Player-Missile Sprites ====
 <syntaxhighlight lang="6502">

@@ Line 21: / Line 21: @@
 ==== Sync with frame  ====
 <syntaxhighlight lang="6502">
-RTCLOK      equ $0012
+       lda 20
-       lda RTCLOK+2
+waitframe:
-waits
+       cmp 20
-       cmp RTCLOK+2
+       beq waitframe
 </syntaxhighlight>
-Or if you don't mind trashing RTCLOK
+Or a shorter version if you don't mind trashing RTCLOK (20)
 <syntaxhighlight lang="6502">
-RTCLOK      equ $0012
+waitframe
-waits
+       lsr 20
-       lsr RTCLOK+2
+       bcc waitframe
 </syntaxhighlight>
 ==== Getting something on screen ====

@@ Line 144: / Line 144: @@
 * https://en.wikipedia.org/wiki/POKEY
-==== BASIC ====
+==== Make some noise ====
 <syntaxhighlight lang="6502">
 ; from Analog, 1985-09,pp.25-32
@@ Line 169: / Line 170: @@
   jmp *
 </syntaxhighlight>
 === Additional Resources ===

@@ Line 7: / Line 7: @@
 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/
+* Assembler: MADS Assembler - This assembler can create atari XEX files out of the box. 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.
+* Emulator(s): I Found Altirra to work best for my usecases. Make sure to use the original Rev2 rom for best compatibility.
 ==== Special Memory Adresses ====