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amiga-bootcamp/01_hardware/ocs_a500/README.md
Ilia Sharin 21751c0025 docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections 
Comprehensive technical documentation covering:
- Hardware: OCS/ECS/AGA custom chip registers, Copper & Blitter deep dives
- Boot sequence: cold boot through startup-sequence
- Binary format: HUNK executable spec, relocation, debug info
- Linking & ABI: .fd files, LVO tables, register calling conventions
- Exec kernel: tasks, interrupts, memory, signals, semaphores
- AmigaDOS: file I/O, FFS/OFS layout, CLI/Shell scripting
- Graphics: planar bitmaps, Copper programming, HAM/EHB modes
- Intuition: screens, windows, IDCMP, BOOPSI
- Devices: trackdisk, SCSI, serial, timer, audio, keyboard
- Libraries: utility, expansion, IFFParse, locale, ARexx
- Networking: bsdsocket API, SANA-II, TCP/IP stack comparison
- Toolchain: GCC, vasm/vlink, SAS/C, NDK, debugging
- Reverse engineering: IDA/Ghidra setup, compiler fingerprints, case studies
- CPU & MMU: 68040/060 emulation libs, PMMU, cache management
- Driver development: SANA-II, Picasso96/RTG, AHI audio

All files include breadcrumb navigation. No local paths or proprietary content.
2026-04-23 12:17:35 -04:00

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← Home · Hardware

OCS Chipset — A500 / A1000 / A2000

Overview

The Original Chip Set (OCS) ships in the Amiga 1000 (1985), A500 (1987), and early A2000 boards. It consists of three custom chips: Agnus, Denise, and Paula, supported by the MOS 8520 CIA pair.

Chip Summary

Chip MOS Part Primary Responsibilities
Agnus 8361 (PAL), 8367 (NTSC) DMA controller, Copper coprocessor, Blitter, address generation
Denise 8362 Display: bitplane fetch decode, sprite decode, colour output
Paula 8364 Audio DMA (4 channels), floppy disk I/O, serial port, interrupts

Contents

File Topic
chipset_ocs.md Chip internals, DMA priorities, bus arbitration
custom_registers.md Full OCS register map $DFF000–$DFF1FE
copper.md Copper coprocessor: WAIT/SKIP/MOVE, copperlist format
blitter.md Blitter: channels A/B/C/D, minterms, line mode, fill
paula_audio.md Audio DMA: AUDxLCH/LCL/LEN/PER/VOL, interrupt
paula_serial.md Serial port: SERPER/SERDATR, baud rate
sprites.md Hardware sprites: SPRxPTH, control words, attach mode

OCS Limitations vs ECS/AGA

  • Max 512 KB Chip RAM on A500 rev 5 and earlier (Agnus 8361/8367 addresses 512 KB only)
  • A500 rev 6+ allows 1 MB with Fat Agnus (part of later OCS run)
  • No productivity display modes (ECS adds BEAMCON0)
  • 32 colours max (or 64 EHB, or HAM 12-bit) in standard bitplane modes
  • Blitter is 16-bit; no 64-bit fetch (AGA adds FMODE)
  • No ECS Denise border features

References