mirror of
https://github.com/alfishe/amiga-bootcamp.git
synced 2026-06-13 00:26:28 +00:00
128 lines
4.4 KiB
Markdown
128 lines
4.4 KiB
Markdown
[← Home](../../README.md) · [Hardware](../README.md) · [OCS](README.md)
|
||
|
||
# Copper Coprocessor
|
||
|
||
## Overview
|
||
|
||
The **Copper** (co-processor) is built into Agnus. It executes a simple instruction list (the **copperlist**) in sync with the video beam, allowing precise per-scanline changes to any writable custom register — without CPU intervention.
|
||
|
||
The Copper can only write to custom registers (it cannot access Chip RAM directly), but it can change bitplane pointers, colors, BPLCON0, sprite pointers, and any other `$DFF0xx` register on a cycle-accurate basis.
|
||
|
||
## Copper Instruction Set
|
||
|
||
The Copper has exactly **three instructions**, each exactly **32 bits** (two 16-bit words):
|
||
|
||
### 1. MOVE — Write a Register
|
||
|
||
```
|
||
Word 1: [RRR RRRR RRR0] Destination register address (must be even, bit 0 = 0)
|
||
Word 2: [DDDD DDDD DDDD] Data to write
|
||
```
|
||
|
||
Example — set COLOR00 to red at scanline 100:
|
||
```
|
||
DC.W $0180, $0F00 ; MOVE COLOR00, $0F00 (red)
|
||
```
|
||
|
||
### 2. WAIT — Wait for Beam Position
|
||
|
||
```
|
||
Word 1: [VVVV VVVH HHHH HH1] Vertical pos[8:1], Horizontal pos[8:3], bit0=1
|
||
Word 2: [EVVV VVVH HHHH HHx0] Enable, VP mask, HP mask, bit0=0
|
||
```
|
||
|
||
The Copper stalls until the beam reaches `(V,H) AND (Vmask,Hmask)`.
|
||
|
||
Standard full-precision WAIT:
|
||
```
|
||
DC.W $6401, $FF00 ; WAIT for line $64 (100), any H — full V mask
|
||
```
|
||
|
||
WAIT for end of frame (copper stop):
|
||
```
|
||
DC.W $FFFF, $FFFE ; WAIT $FF,$FF — impossible position → stop copper
|
||
```
|
||
|
||
### 3. SKIP — Conditional Skip
|
||
|
||
```
|
||
Word 1: [VVVV VVVH HHHH HH1] Same format as WAIT
|
||
Word 2: [EVVV VVVH HHHH HHx1] Same as WAIT but bit 0 = 1 (SKIP flag)
|
||
```
|
||
|
||
If beam has passed the position, skip the next instruction. Used for double-buffered copper switching.
|
||
|
||
## Copperlist Format
|
||
|
||
A copperlist is an array of 32-bit instruction pairs in **Chip RAM**, terminated by:
|
||
```
|
||
DC.W $FFFF, $FFFE
|
||
```
|
||
|
||
Example — color cycle on vertical blank:
|
||
```asm
|
||
Copperlist:
|
||
DC.W $0180, $0000 ; COLOR00 = black
|
||
DC.W $4401, $FF00 ; WAIT line 68 (display area start)
|
||
DC.W $0180, $0F00 ; COLOR00 = red
|
||
DC.W $6401, $FF00 ; WAIT line 100
|
||
DC.W $0180, $00F0 ; COLOR00 = green
|
||
DC.W $FFFF, $FFFE ; END
|
||
```
|
||
|
||
## Copper Pointers and Control
|
||
|
||
| Register | Offset | Description |
|
||
|---|---|---|
|
||
| COP1LCH | $080 | Copper list 1 pointer high word |
|
||
| COP1LCL | $082 | Copper list 1 pointer low word |
|
||
| COP2LCH | $084 | Copper list 2 pointer high word |
|
||
| COP2LCL | $086 | Copper list 2 pointer low word |
|
||
| COPJMP1 | $088 | Strobe: restart copper from list 1 (any write) |
|
||
| COPJMP2 | $08A | Strobe: restart copper from list 2 |
|
||
| COPCON | $02E | Copper danger bit (CDANG) |
|
||
|
||
**COPCON** bit 1 (`CDANG`): When set, Copper is allowed to write to registers `$40`–`$7F` (blitter registers). Should be 0 in normal use to prevent runaway copperlists from corrupting the blitter.
|
||
|
||
## Activating the Copper
|
||
|
||
```asm
|
||
; Load copperlist address into copper list 1
|
||
move.l #Copperlist, d0
|
||
move.w d0, COP1LCL+custom ; low word
|
||
swap d0
|
||
move.w d0, COP1LCH+custom ; high word
|
||
|
||
; Restart copper (triggers on next VBlank)
|
||
move.w d0, COPJMP1+custom ; value irrelevant, strobe only
|
||
|
||
; Enable copper DMA
|
||
move.w #$8280, DMACON+custom ; SET + MASTER + COPEN
|
||
```
|
||
|
||
## Dual-Playfield and HAM via Copper
|
||
|
||
Common copper techniques:
|
||
|
||
**Split-screen different palettes:** Change `COLOR00`–`COLOR31` registers mid-screen via a WAIT at the split scanline.
|
||
|
||
**Mid-screen bitplane pointer change:** Redirect `BPL1PTH/BPL1PTL` to a different bitmap half-way through the display — used for large vertical scrolling without double-buffering the full screen.
|
||
|
||
**BPLCON0 mid-screen:** Switch between `HIRES` and `LORES`, or between 6-plane and 4-plane modes, on different lines.
|
||
|
||
**Raster bars:** Write a different color to COLOR00 on every scanline using sequential WAIT+MOVE pairs.
|
||
|
||
## Graphics Library vs Direct Copper
|
||
|
||
AmigaOS's `graphics.library` manages the Copper list internally:
|
||
- `MrgCop()` merges system and user copper lists
|
||
- `LoadView()` installs a View structure's copper list
|
||
- `WaitTOF()` waits for the top-of-frame (VBlank) before the copper restarts
|
||
|
||
Direct copper access should be done via `GetColorMap()`, `SetRGB4()` and official graphics calls, or through a custom `View`/`ViewPort`/`ColorMap` structure passed to `LoadView()`.
|
||
|
||
## References
|
||
|
||
- ADCD 2.1 Hardware Manual — Copper chapter
|
||
- NDK39: `hardware/custom.h`, `graphics/copper.h`
|
||
- *Amiga Hardware Reference Manual* 3rd ed., Chapter 6
|