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Peripherals and models description improved and expanded
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01_hardware/aga_a1200_a4000/akiko_cd32.md
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01_hardware/aga_a1200_a4000/akiko_cd32.md
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[← Home](../../README.md) · [Hardware](../README.md) · [AGA](README.md)
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# Akiko — CD32 Custom Chip
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## Overview
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The **Akiko** chip is a custom ASIC unique to the Amiga CD32 game console (1993). It sits alongside the standard AGA chipset (Alice + Lisa + Paula) and provides three subsystems that exist in no other Amiga model:
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1. **Chunky-to-Planar (C2P) conversion** — hardware-accelerated pixel format conversion
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2. **CD-ROM controller** — drives the internal double-speed CD-ROM
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3. **NVRAM interface** — I²C controller for the onboard serial EEPROM
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Akiko is mapped at base address **`$B80000`** and occupies a 32 KB window (`$B80000`–`$B87FFE`).
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## Chip Identification
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Reading a longword from `$B80000` returns the Akiko ID:
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```asm
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move.l $B80000, d0 ; d0 = $C0CACAFE if Akiko present
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cmp.l #$C0CACAFE, d0
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beq .has_akiko
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```
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> [!NOTE]
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> On non-CD32 machines, reading `$B80000` will return bus noise or trigger a bus error. Always wrap Akiko detection in an exception handler or use `graphics.library` v40+ `WriteChunkyPixels()` which auto-detects Akiko internally.
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## Register Map
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| Offset | Name | R/W | Description |
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|---|---|---|---|
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| `$B80000` | `AKIKO_ID` | R | Chip ID — returns `$C0CACAFE` |
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| `$B80002` | `AKIKO_REV` | R | Silicon revision |
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| `$B80004` | `AKIKO_INTREQ` | R | Interrupt request (CD subcode, C2P done) |
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| `$B80008` | `AKIKO_INTENA` | RW | Interrupt enable mask |
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| `$B80010` | `CDROM_PBXSTAT` | RW | CD-ROM PIO buffer/status |
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| `$B80014` | `CDROM_FLAGS` | RW | CD-ROM control flags |
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| `$B80018` | `CDROM_TXDATA` | W | CD-ROM command transmit |
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| `$B8001C` | `CDROM_RXDATA` | R | CD-ROM response receive |
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| `$B80020` | `CDROM_SUBCDATA` | R | CD subcode (Q-channel) data |
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| `$B80024` | `NVRAM_CTRL` | RW | NVRAM I²C control (SCL/SDA direction) |
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| `$B80028` | `NVRAM_DATA` | RW | NVRAM I²C data (SCL/SDA bit-bang) |
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| `$B80030` | `C2P_INPUT` | W | Chunky-to-Planar input register (longword) |
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| `$B80030` | `C2P_OUTPUT` | R | Chunky-to-Planar output register (longword) |
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> [!IMPORTANT]
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> The register map above is reverse-engineered from WinUAE (`akiko.cpp`) and community hardware testing. Commodore never published an official Akiko datasheet.
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---
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## Chunky-to-Planar (C2P) Conversion
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### The Problem
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The AGA chipset uses **planar** graphics — each bitplane is a separate contiguous block of memory. But most game engines (especially PC ports) render in **chunky** format — one byte per pixel in a linear framebuffer. Converting between these formats is computationally expensive on the 68020.
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### How Akiko C2P Works
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Akiko converts **32 chunky pixels** (8-bit each) into **8 bitplane longwords** in hardware. The CPU must feed data in and read results out — Akiko has **no DMA**; it is a register-based pipeline.
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#### Conversion Protocol
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```
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Input: 8 longwords of chunky data (4 pixels × 8 = 32 pixels)
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Output: 8 longwords of planar data (1 longword per bitplane × 8 planes)
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```
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**Step 1 — Write 8 longwords of chunky pixels:**
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```asm
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; a0 = source chunky buffer (32 pixels = 32 bytes, read as 8 longwords)
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; Each longword contains 4 consecutive 8-bit pixels: [P0|P1|P2|P3]
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lea $B80030, a1 ; C2P input register
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move.l (a0)+, (a1) ; pixels 0–3
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move.l (a0)+, (a1) ; pixels 4–7
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move.l (a0)+, (a1) ; pixels 8–11
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move.l (a0)+, (a1) ; pixels 12–15
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move.l (a0)+, (a1) ; pixels 16–19
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move.l (a0)+, (a1) ; pixels 20–23
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move.l (a0)+, (a1) ; pixels 24–27
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move.l (a0)+, (a1) ; pixels 28–31
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```
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**Step 2 — Read 8 longwords of planar output:**
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```asm
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; a2 = destination planar buffer (8 bitplanes × 4 bytes = 32 bytes)
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lea $B80030, a1 ; C2P output register (same address, read mode)
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move.l (a1), (a2)+ ; bitplane 0 (32 pixels, 1 bit each)
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move.l (a1), (a2)+ ; bitplane 1
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move.l (a1), (a2)+ ; bitplane 2
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move.l (a1), (a2)+ ; bitplane 3
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move.l (a1), (a2)+ ; bitplane 4
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move.l (a1), (a2)+ ; bitplane 5
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move.l (a1), (a2)+ ; bitplane 6
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move.l (a1), (a2)+ ; bitplane 7
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```
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#### Optimised Loop (MOVEM)
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In practice, the entire 32-pixel conversion is done with two MOVEM instructions:
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```asm
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; Convert 32 chunky pixels → 8 planar longwords
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; a0 = chunky source, a2 = planar dest
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; a1 = $B80030 (Akiko C2P register)
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movem.l (a0)+, d0-d7 ; load 32 chunky pixels (8 longwords)
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movem.l d0-d7, (a1) ; write to Akiko C2P input
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movem.l (a1), d0-d7 ; read 8 planar longwords from Akiko
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movem.l d0-d7, (a2) ; store to bitplane memory
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lea 32(a2), a2 ; advance planar pointer
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```
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> [!WARNING]
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> MOVEM to a fixed address writes all registers to the **same** address (FIFO-style), which is exactly what Akiko expects. This only works because `$B80030` is a hardware register, not normal RAM.
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#### Full-Screen Conversion Example
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For a 320×256 screen at 8 bitplanes (256 colours):
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```asm
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; Total pixels = 320 × 256 = 81,920
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; Each pass converts 32 pixels → 81,920 / 32 = 2,560 passes
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lea chunky_buffer, a0
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lea planar_buffer, a2
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lea $B80030, a1
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move.l #2560-1, d7 ; loop counter
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.c2p_loop:
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movem.l (a0)+, d0-d6/a3 ; 8 longwords (use a3 for 8th reg)
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movem.l d0-d6/a3, (a1) ; write to Akiko
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movem.l (a1), d0-d6/a3 ; read planar output
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movem.l d0-d6/a3, (a2)
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lea 32(a2), a2
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dbf d7, .c2p_loop
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```
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### Performance Characteristics
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| Metric | Value |
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|---|---|
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| Pixels per pass | 32 |
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| CPU cycles per pass | ~80–100 (68020 @ 14 MHz) |
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| Throughput | ~1.5 MB/s (register I/O bound) |
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| 320×256×8bpp full screen | ~54 ms (~18 fps standalone) |
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#### When to Use Akiko C2P
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| Scenario | Recommendation |
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|---|---|
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| Stock CD32 (68020, Chip RAM only) | **Use Akiko** — significantly faster than CPU-only C2P |
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| CD32 + SX-32 with 68030 + Fast RAM | Benchmark both — software C2P may match Akiko |
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| CD32 + 68040/060 accelerator | **Use software C2P** — CPU is 5–10× faster than Akiko's throughput |
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### AmigaOS Interface
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OS-compliant applications use `WriteChunkyPixels()` from `graphics.library` v40+:
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```c
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#include <graphics/gfx.h>
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/* graphics.library auto-detects Akiko and uses it if present */
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WriteChunkyPixels(
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rp, /* RastPort */
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xstart, ystart, /* top-left corner */
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xstop, ystop, /* bottom-right corner */
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chunky_array, /* source chunky pixel data */
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bytes_per_row /* chunky buffer pitch */
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);
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```
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---
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## CD-ROM Controller
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### Hardware
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The CD32 contains a **Philips/Sony double-speed (2×) CD-ROM** drive. Unlike the CDTV (which uses a SCSI-based controller via DMAC/WD33C93), the CD32's CD-ROM is controlled **directly by Akiko** through a proprietary PIO interface.
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### Drive Capabilities
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| Feature | Specification |
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|---|---|
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| Speed | 2× (300 KB/s data, 150 KB/s audio) |
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| Media | CD-ROM (Mode 1/2), CD-DA, Mixed Mode |
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| Seek | ~400 ms average |
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| Interface | Akiko PIO (no SCSI, no IDE) |
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### CD-ROM Register Protocol
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Communication with the drive is command/response based through the Akiko registers:
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1. **Write command bytes** to `CDROM_TXDATA` (`$B80018`)
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2. **Poll status** via `CDROM_PBXSTAT` (`$B80010`) for response availability
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3. **Read response bytes** from `CDROM_RXDATA` (`$B8001C`)
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4. **Read subcode** from `CDROM_SUBCDATA` (`$B80020`) for TOC/position data
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### Boot from CD
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The CD32 boots exclusively from CD-ROM (no floppy drive). The boot sequence:
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1. Kickstart 3.1 initialises from ROM (`$F80000`)
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2. Extended ROM at `$E00000` provides `cd.device` and the CD filesystem
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3. Akiko initialises the CD-ROM drive
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4. The system reads the TOC and looks for a boot block (Amiga executable format)
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5. If found, the boot executable is loaded and run — this is the game/application entry point
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> [!NOTE]
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> CD32 game discs use standard ISO 9660 with Amiga-specific boot blocks. Many titles also include CD-DA audio tracks for music, played via Akiko's CDDA passthrough.
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---
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## NVRAM (Non-Volatile Storage)
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### Hardware
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The CD32 includes a **1 Kbit (128 bytes) serial EEPROM** (typically a 93C46 or compatible) accessed via I²C bit-banging through Akiko registers.
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| Parameter | Value |
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|---|---|
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| Type | Serial EEPROM (I²C / Microwire) |
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| Capacity | 1 Kbit (128 bytes usable) |
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| Interface | Akiko bit-bang (SCL/SDA via `$B80024`/`$B80028`) |
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| Persistence | Battery-backed (CR2032) |
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| Typical use | Game saves, system preferences, high scores |
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### Access Protocol
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NVRAM access requires bit-banging the I²C clock (SCL) and data (SDA) lines through Akiko registers:
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```asm
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; Simplified NVRAM byte read
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; d0 = address (0–127)
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; Set SDA as output, clock high
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move.l #$01, $B80024 ; NVRAM_CTRL: configure direction
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; Send device address + read command via bit-bang
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; (full protocol requires start condition, address bits, ack)
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; Clock in 8 data bits
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moveq #7, d1
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.read_bit:
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bset #0, $B80028 ; SCL high
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move.l $B80028, d2 ; read SDA
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bclr #0, $B80028 ; SCL low
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roxl.b #1, d0 ; shift bit into result
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dbf d1, .read_bit
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```
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### AmigaOS NVRAM Access
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The OS provides `nonvolatile.library` for structured NVRAM access:
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```c
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#include <libraries/nonvolatile.h>
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/* Store data */
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StoreNV("MyGame", "SaveSlot1", save_data, data_length, TRUE);
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/* Retrieve data */
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APTR data = GetNV("MyGame", "SaveSlot1", TRUE);
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```
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---
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## CD32 Expansion Options
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The CD32 has **no standard expansion slots** (no Zorro, no CPU slot, no trapdoor, no PCMCIA). Third-party units connect via the rear expansion port:
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### SX-1 (Paravision)
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| Feature | Specification |
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|---|---|
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| Memory | 1× 72-pin SIMM (1–8 MB Fast RAM) |
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| Storage | Internal 44-pin IDE (2.5" HDD) + external DB37 IDE |
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| I/O | Parallel (DB25), Serial (9-pin RS232), RGB video (DB23) |
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| Keyboard | AT-101 connector |
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| Floppy | External DB23 floppy connector |
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| Other | RTC (CR2032), FMV pass-through, disable switch |
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### SX-32 / SX-32 Pro (DCE)
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| Feature | Specification |
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|---|---|
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| Memory | 1× 72-pin SIMM (up to 8 MB) |
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| Storage | Internal 44-pin IDE |
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| I/O | Parallel (DB25), Serial (DB25), RGB (DB23), VGA (HD15) |
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| CPU upgrade | SX-32 Pro includes 68030 socket |
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| Other | RTC, external floppy |
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### FMV Module (Commodore)
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| Feature | Specification |
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|---|---|
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| Function | MPEG-1 video + audio decoder (Video CD playback) |
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| Video chip | C-Cube CL450 MPEG decoder |
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| Audio chip | LSI Logic audio decoder |
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| Limitation | Caps system Fast RAM at 4 MB |
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| Compatibility | Works with SX-1 (pass-through); **incompatible** with SX-32 |
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> [!WARNING]
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> The FMV module had four hardware revisions. Early revisions (rev 1–2) are prone to overheating. If sourcing one today, look for rev 3 or later.
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---
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## CD32 vs A1200 — Hardware Comparison
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The CD32 is often described as "an A1200 in a console shell." The chipset is identical, but the system-level hardware differs significantly:
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| Feature | A1200 | CD32 |
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|---|---|---|
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| CPU | 68EC020 @ 14 MHz | 68EC020 @ 14 MHz |
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| Custom chips | Alice + Lisa + Paula | Alice + Lisa + Paula + **Akiko** |
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| Chip RAM | 2 MB | 2 MB |
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| Chipset | AGA | AGA |
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| Storage | IDE (Gayle), Floppy | **CD-ROM (Akiko)**, no floppy |
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| Expansion | Trapdoor (150-pin), PCMCIA | Rear port only (SX-1/SX-32) |
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| Keyboard | Built-in | None (requires SX-1/SX-32) |
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| Controller | Atari-style DB9 joystick | **CD32 gamepad** (7-button protocol) |
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| NVRAM | None | **128 bytes EEPROM** (Akiko) |
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| Gayle | Yes (IDE, PCMCIA) | **No** — Akiko replaces storage functions |
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| C2P hardware | No | **Yes** (Akiko) |
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| Boot media | Floppy / HDD | CD-ROM only |
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### CD32 Gamepad Protocol
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The CD32 gamepad uses a serial shift-register protocol through the standard DB9 controller port, providing 7 buttons:
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| Button | Bit | Accent |
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|---|---|---|
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| Blue (Play) | 0 | Fire 1 / primary action |
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| Red (Rewind) | 1 | Fire 2 / secondary |
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| Yellow (FF) | 2 | Fire 3 |
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| Green (Stop) | 3 | Fire 4 |
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| Right shoulder | 4 | Shoulder R |
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| Left shoulder | 5 | Shoulder L |
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| Pause | 6 | Start/Pause |
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Detection: the CD32 pad responds to a clock signal on pin 5 of the joystick port. Standard Atari-style joysticks ignore this signal and remain compatible.
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---
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## Detecting CD32 at Runtime
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```c
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#include <exec/execbase.h>
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/* Method 1: Check Akiko ID register (hardware-level) */
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BOOL has_akiko(void)
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{
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volatile ULONG *akiko_id = (ULONG *)0xB80000;
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/* Wrap in exception handler — bus error on non-CD32 */
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return (*akiko_id == 0xC0CACAFE);
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}
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/* Method 2: Check for CD32 via expansion.library (safer) */
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#include <libraries/configvars.h>
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#include <clib/expansion_protos.h>
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BOOL is_cd32(void)
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{
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/* Akiko autoconfig: manufacturer 0x0202, product 0x3E */
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struct ConfigDev *cd = FindConfigDev(NULL, 0x0202, 0x3E);
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return (cd != NULL);
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}
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```
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## References
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- WinUAE source: `akiko.cpp` — reverse-engineered register definitions (Toni Wilen)
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- Commodore CD32 Technical Reference (internal, partial — never publicly released)
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- NDK39: `graphics/gfx.h` — `WriteChunkyPixels()` prototype
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- NDK39: `libraries/nonvolatile.h` — NVRAM access API
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- [Big Book of Amiga Hardware — CD32](https://bigbookofamigahardware.com/)
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- English Amiga Board (EAB) — CD32 hardware discussions
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## See Also
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- [AGA Chipset Internals](chipset_aga.md) — Alice and Lisa (shared with CD32)
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- [Memory Types](../common/memory_types.md) — CD32 memory configuration
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- [Address Space](../common/address_space.md) — CD32 address map with Akiko region
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