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107 lines
4.3 KiB
Markdown
107 lines
4.3 KiB
Markdown
[← Home](../../README.md) · [Hardware](../README.md)
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# AGA Chipset — A1200 / A4000 / CD32
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## Overview
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The **Advanced Graphics Architecture** (AGA) is the final custom chipset developed by Commodore, shipping from 1992. It dramatically expands color depth, palette size, sprite capabilities, and blitter bandwidth while retaining full OCS/ECS backward compatibility.
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## Chip Summary
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| Chip | Name | Changes from ECS |
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|---|---|---|
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| **Alice** | MOS 8374 | Super Agnus successor: 64-bit bus, FMODE register |
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| **Lisa** | (unnamed MOS) | ECS Denise successor: 8-bit palette, 256 colors |
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| **Paula** | MOS 8364 | Unchanged from OCS/ECS |
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## Contents
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| File | Topic |
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|---|---|
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| [chipset_aga.md](chipset_aga.md) | Alice and Lisa internals, AGA architecture |
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| [aga_registers_delta.md](aga_registers_delta.md) | New/changed registers vs ECS |
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| [aga_palette.md](aga_palette.md) | 24-bit color system, 256 registers |
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| [aga_display_modes.md](aga_display_modes.md) | HAM8, 256-color, doublescan, VGA |
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| [aga_blitter.md](aga_blitter.md) | 64-bit blitter bus, FMODE |
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| [aga_copper.md](aga_copper.md) | AGA Copper programming guide |
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| [cpu_030_040.md](cpu_030_040.md) | 68030/040 on A3000/A4000: cache, MMU, FPU |
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| [akiko_cd32.md](akiko_cd32.md) | CD32 Akiko chip: C2P conversion, CD-ROM, NVRAM |
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| [Gayle IDE & PCMCIA](../common/gayle_ide_pcmcia.md) | A1200 Gayle: IDE and PCMCIA (shared with A600) |
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## AGA vs ECS — Key Differences
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| Feature | ECS | AGA |
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|---|---|---|
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| Color registers | 32 (12-bit) | **256 (24-bit)** |
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| Max simultaneous colors | 64 EHB / HAM | **256** (or HAM8: 262,144) |
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| Blitter bus | 16-bit | **64-bit** (FMODE) |
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| Sprite width | 16 px | **64 px** |
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| Sprite colors | 3+transparent | **15+transparent** (64-color attached) |
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| Bitplane depth | 6 planes max | **8 planes** |
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| Palette select | 1 bank | **4 bitplane banks, 4 sprite banks** |
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## Identifying AGA at Runtime
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```c
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#include <graphics/gfxbase.h>
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extern struct GfxBase *GfxBase;
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BOOL is_aga = (GfxBase->ChipRevBits0 & (1 << GFXB_AA_ALICE)) != 0;
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```
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| ChipRevBits0 bit | Flag | Meaning |
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|---|---|---|
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| 4 | `GFXB_AA_ALICE` | AGA Alice present |
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| 5 | `GFXB_AA_LISA` | AGA Lisa present |
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---
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## AGA Machines — Per-Model Details
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| Model | CPU | Notes |
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|---|---|---|
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| A1200 | 68EC020 14 MHz | Budget AGA; Gayle IDE; PCMCIA; 2 MB Chip |
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| A4000 | 68030/040 25 MHz | High-end; Zorro III; IDE; 2 MB Chip + Fast |
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| A4000T | 68040/060 | Tower variant; SCSI |
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| CD32 | 68EC020 14 MHz | Game console; Akiko C2P; CD-ROM; no keyboard |
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### CD32 (1993) — AGA Game Console
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The CD32 uses the **identical AGA chipset** (Alice + Lisa + Paula) as the A1200, but adds the **Akiko** custom chip — a unique ASIC providing:
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- **Chunky-to-Planar (C2P) hardware conversion** — converts 8-bit linear pixel data to planar bitplane format
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- **CD-ROM controller** — drives the internal double-speed CD-ROM via PIO (no SCSI, no IDE)
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- **NVRAM interface** — I²C controller for 128-byte onboard EEPROM
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The CD32 has **no Gayle chip** — Akiko replaces all storage functions. It has no keyboard, no floppy, no Zorro slots, and no PCMCIA. The only expansion path is the rear port (SX-1/SX-32 add-on units) or the FMV module slot.
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See the dedicated article: **[Akiko — CD32 Custom Chip](akiko_cd32.md)**
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### A4000T (1994) — Tower Workstation
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The A4000T is the tower variant of the A4000 desktop, adding:
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| Feature | A4000 Desktop | A4000T Tower |
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|---|---|---|
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| CPU | 68030 @ 25 MHz or 68040 @ 25 MHz | 68040 @ 25 MHz or 68060 @ 50 MHz |
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| SCSI | None | **NCR53C710** (Fast SCSI-2, bus-mastering DMA) |
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| Drive bays | 1× 3.5" IDE | 3× 5.25" + 1× 3.5" |
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| Zorro III | 4 slots | 5 slots |
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| CPU slot | Yes | Yes (enhanced pinout) |
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| Power supply | Internal 150W | Internal 300W |
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| IDE | On-board (Gayle-less) | On-board + SCSI |
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The A4000T's **NCR53C710** SCSI controller is a high-performance bus-mastering DMA controller — significantly faster than the WD33C93 used in the A3000 and CDTV. It supports up to 7 SCSI devices on an internal 50-pin ribbon cable.
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> [!NOTE]
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> The A4000T was the last Amiga produced by Commodore before the company's bankruptcy in April 1994. Very few units were manufactured, making it one of the rarest stock Amiga models.
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---
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## References
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- ADCD 2.1 Hardware Manual — AGA chapters
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- NDK39: `graphics/gfxbase.h`, `hardware/custom.h`
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- Commodore A1200/A4000 Technical Reference Manuals (local archive)
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