Copper List Basics

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. Every Amiga program needs a copper list.

Code

; =============================================================================
; 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

            ; --- 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

            ; --- 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  #$83a0,DMACON(a5)   ; Master + copper + sprites + bitplanes

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)

; === SPRITE DATA ===
            even
sprite_data:
            dc.w    $6050,$7000         ; Control words (Y=96, X=80, height=16)
            ; 16 lines of sprite graphics
            dc.w    $0000,$0000
            dc.w    $07e0,$0000
            dc.w    $1ff8,$0420
            ; ... more sprite data ...
            dc.w    $0000,$0000         ; End marker

Trade-offs

Aspect	Cost
CPU	None (copper runs independently)
Memory	4 bytes per MOVE, 4 bytes per WAIT
Limitation	Can only write to custom chip registers

When to use: All Amiga programs. You need a copper list for any graphics.

When to avoid: Never - it's mandatory for display setup.

Copper Instructions

The copper understands only two instructions:

WAIT

Wait for the beam to reach a position:

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:

dc.w    REGISTER,VALUE

Register must be in range $000-$1FE
Writes happen instantly when the beam reaches that position

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:

$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:

        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: VBlank Game Loop, Sprite Control Words

Vault: Commodore Amiga | Copper