Code Like It's 198x

Copper List Basics

Build a copper list to set colours and sprite pointers. The foundation of all Amiga graphics programming.

Code status: illustrative code. Adapt the listing to your program and check it on your target machine. This page links no assembly or execution record for the listing itself.

Overview

The Copper is a coprocessor that executes a list of instructions in sync with the display beam. It can wait for specific scanlines and write to custom chip registers, enabling per-scanline colour changes, sprite multiplexing, and complex visual effects. A dedicated graphics program can use its own list; an OS-managed application can leave display setup to the system.

Code

68000 assembly
; =============================================================================
; COPPER LIST BASICS - AMIGA
; Simple copper list with colours and sprite pointer
; Taught: Game 1 (Signal), Unit 1
; Memory: Variable (depends on complexity)
; =============================================================================

CUSTOM      equ $dff000
COP1LC      equ $080            ; Copper list 1 pointer
COPJMP1     equ $088            ; Copper jump strobe
DMACON      equ $096
COLOR00     equ $180            ; Background colour
SPR0PTH     equ $120            ; Sprite 0 pointer high
SPR0PTL     equ $122            ; Sprite 0 pointer low

            section code,code_c

start:
            lea     CUSTOM,a5

            move.w  #$7fff,$09a(a5)    ; exclusive, reset-to-leave caller
            move.w  #$7fff,$09c(a5)
            move.w  #$7fff,DMACON(a5)
            move.w  #$0200,$100(a5)     ; colour display, zero bitplanes

            ; --- Set sprite pointer in copper list ---
            lea     sprite_data,a0
            move.l  a0,d0
            swap    d0                  ; High word first
            lea     sprpth_val,a1
            move.w  d0,(a1)             ; Store high word
            swap    d0
            lea     sprptl_val,a1
            move.w  d0,(a1)             ; Store low word

            ; Disabled sprite blocks for the other seven DMA channels.
            lea     disabled_sprite,a0
            move.l  a0,d0
            lea     $dff128,a0
            moveq   #6,d1
.clear_other_sprites:
            move.l  d0,(a0)
            addq.l  #8,a0
            dbra    d1,.clear_other_sprites

            ; --- Install copper list ---
            lea     copperlist,a0
            move.l  a0,COP1LC(a5)       ; Set copper list address
            move.w  d0,COPJMP1(a5)      ; Strobe to start copper

            ; --- Enable DMA ---
            move.w  #$82a0,DMACON(a5)   ; Master + copper + sprites

mainloop:
            bra.s   mainloop

; === COPPER LIST ===
copperlist:
            ; Set background colour
            dc.w    COLOR00,$0048       ; Blue background

            ; Set sprite palette (colours 17-19)
            dc.w    $01a2,$00f0         ; Sprite colour 1: bright green
            dc.w    $01a4,$0ff0         ; Sprite colour 2: yellow
            dc.w    $01a6,$0000         ; Sprite colour 3: black

            ; Sprite 0 pointer (filled in by code)
            dc.w    SPR0PTH
sprpth_val: dc.w    $0000
            dc.w    SPR0PTL
sprptl_val: dc.w    $0000

            ; Wait for specific scanline and change colour
            dc.w    $8007,$fffe         ; WAIT for line $80
            dc.w    COLOR00,$0080       ; Change to green

            dc.w    $c007,$fffe         ; WAIT for line $C0
            dc.w    COLOR00,$0444       ; Change to grey

            ; End copper list
            dc.w    $ffff,$fffe         ; WAIT forever (end marker)

disabled_sprite: dc.w 0,0

; === SPRITE DATA ===
            even
sprite_data:
            dc.w    $6050,$7000         ; Control words (beam Y=96, beam X=160, height=16)
            ; Sixteen rows, two words per row.
            dc.w $0000,0,$07e0,0,$1ff8,0,$3ffc,0
            dc.w $7ffe,0,$ffff,0,$ffff,0,$ffff,0
            dc.w $ffff,0,$ffff,0,$ffff,0,$7ffe,0
            dc.w $3ffc,0,$1ff8,0,$07e0,0,$0000,0
            dc.w    $0000,$0000         ; End marker

Trade-offs

Aspect Cost
CPU No per-line polling; list setup and patching still cost CPU time
Memory 4 bytes per MOVE, 4 bytes per WAIT
Limitation Can only write to custom chip registers

When to use: A dedicated display needing beam-synchronised custom-register writes.

When to avoid: An OS-managed window where the graphics system owns the display.

Copper Instructions

MOVE and WAIT are the main instructions used here; SKIP is described below.

WAIT

Wait for the beam to reach a position:

Code
dc.w    $VVHH,$fffe
  • VV = Vertical position (scanline, $00-$FF)
  • HH = Horizontal position (usually $07 for “any horizontal”)
  • $fffe = WAIT instruction marker

MOVE

Write a value to a register:

Code
dc.w    REGISTER,VALUE
  • Register must be in range $000-$1FE
  • A MOVE needs available Copper bus slots; earlier WAITs and DMA load affect its timing.

Colour Register Reference

Register Purpose
$0180 (COLOR00) Background/border
$0182 (COLOR01) Bitplane colour 1
$0184 (COLOR02) Bitplane colour 2
$01A2-$01A6 (COLOR17-19) Sprites 0 and 1 colours 1, 2, 3
$01AA-$01AE (COLOR21-23) Sprites 2 and 3 colours 1, 2, 3
$01B2-$01B6 (COLOR25-27) Sprites 4 and 5 colours 1, 2, 3
$01BA-$01BE (COLOR29-31) Sprites 6 and 7 colours 1, 2, 3

Sprite palettes are shared in pairs — sprite 0 and sprite 1 both draw from the same three colours. Use attached sprites to combine a pair into a single 15-colour sprite (see Sprite Control Words).

Colour Format

Amiga colours are 12-bit RGB:

Code
$0RGB

Where R, G, B are each 0-F (4 bits).

Examples:

  • $0F00 = Red
  • $00F0 = Green
  • $000F = Blue
  • $0FFF = White
  • $0000 = Black
  • $0888 = Grey

Two copper lists

The Copper has two program pointers: COP1LC ($DFF080) and COP2LC ($DFF084), with corresponding strobes COPJMP1 ($DFF088) and COPJMP2 ($DFF08A). Strobing either one restarts the Copper at that list. A common pattern:

  • COP1 = short setup list run from VBlank — set up display window, palette, restart COP2
  • COP2 = the per-frame “main” list with all the WAIT/MOVE work

To jump from COP1 to COP2: have COP1 end with a strobe-write to COPJMP2, and COP2 ends with dc.w $ffff,$fffe (wait forever). This way you can swap COP2 between frames (double-buffer copper lists) without disturbing COP1.

SKIP instruction

Beyond MOVE and WAIT, the Copper has a SKIP instruction — same word format as WAIT but with bit 0 of the second word set:

68000 assembly
        dc.w    $4007,$ffff             ; SKIP: skip next instruction if beam past line $40
        dc.w    COLOR00,$0f00           ; Skipped if condition met

SKIP enables limited conditional branching. Standard idiom: SKIP followed by a “jump back to start” MOVE that strobes COPJMP1 — a poor-man’s loop.

Patterns: Copper Colour Bars, VBlank Game Loop, Sprite Control Words

Vault: Commodore Amiga | Copper

The list and complete sprite block must be word-aligned Chip RAM and remain valid during DMA. This exclusive boot example has no OS-return path. It changes A0/A1/A5/D0/D1 and condition codes and owns all eight sprite channels, its palette entries, the Copper and background colour. A reusable application must establish its display window/fetch configuration.