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.

01_hardware/aga_a1200_a4000/aga_registers_delta.md

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+[← Home](../../README.md) · [Hardware](../README.md) · [AGA](README.md)
+
+# AGA Register Deltas vs ECS
+
+## New Registers
+
+### FMODE — $DFF1FC (AGA only)
+
+DMA fetch mode — see `chipset_aga.md` for full description.
+
+### BPLCON4 — $DFF10C (AGA only)
+
+Bitplane and sprite colour bank selection:
+
+```
+bits 15-8:  BPLAM7-0  — Bitplane XOR pattern (AGA colour bank XOR)
+bits  7-4:  ESPRM7-4  — Even sprite colour bank (bits 7:4 of colour reg index)
+bits  3-0:  OSPRM7-4  — Odd sprite colour bank
+```
+
+**Bitplane bank select via BPLAM:**
+- BPLAM provides an XOR mask applied to the 8-bit colour index before palette lookup
+- BPLAM = $00 → use COLOR00–COLOR63 (bank 0)
+- BPLAM = $40 → use COLOR64–COLOR127 (bank 1)
+- BPLAM = $80 → use COLOR128–COLOR191 (bank 2)
+- BPLAM = $C0 → use COLOR192–COLOR255 (bank 3)
+
+### COLOR00–COLOR255 — $DFF180–$DFF3BE (AGA)
+
+AGA extends the colour table from 32 registers (OCS/ECS) to **256 registers**.
+
+Each AGA colour register is 32 bits (accessed as two word writes via BPLCON3 latch):
+
+```asm
+; Write 24-bit colour to COLOR00:
+; First write sets high nibble, second sets low nibble
+move.w  #$0000, BPLCON3+custom      ; set LACE=0, select low colour word
+move.w  #$0FFF, COLOR00+custom      ; write $RGB (high 12 bits)
+bset    #9, BPLCON3_shadow           ; set LOCT (low nibble enable)
+move.w  #$0FFF, COLOR00+custom      ; write low nibble of each channel
+```
+
+The standard `LoadRGB32()` and `LoadRGB4()` graphics library calls manage this transparently.
+
+## Changed Registers
+
+### BPLCON2 — $DFF104 (AGA extended)
+
+```
+bits 14-9:  KILLEHB  — kill EHB mode (AGA replaces EHB with 256 colour)
+bit    6:   RDRAM    — read bitplane data from RAM (not registered in Lisa)
+bits   5-3: PF2PRI   — playfield 2 priority
+bits   2-0: PF1PRI   — playfield 1 priority + sprite priority
+```
+
+### BPLCON3 — $DFF106 (AGA extended from ECS)
+
+Additional AGA bits:
+```
+bit 9:    LOCT  — low colour write enable (for 24-bit colour access)
+bit 3:    BRDSPRT — sprites visible in border
+```
+
+## AGA-Specific BPLCON0 Bits
+
+See `chipset_aga.md` — bit 4 is the MSB of the bitplane count for 7/8-plane modes.
+
+## Colour Register Access — Low Nibble Protocol
+
+Writing 24-bit colour to AGA registers requires two steps per colour:
+
+1. **Write high nibble** (standard): `COLOR00 = $0RGB` (bits [11:0] = R[3:0], G[3:0], B[3:0])
+2. **Set LOCT** in BPLCON3 (bit 9)
+3. **Write low nibble**: `COLOR00 = $0rgb` (bits [11:0] = R[3:0], G[3:0], B[3:0], these are the low 4 bits)
+
+This two-write sequence gives 8 bits per channel (R[7:0], G[7:0], B[7:0]) = 24-bit colour.
+
+`LoadRGB32()` does this automatically:
+```c
+/* AGA 32-bit colour table format:
+   Count, then pairs: [colour_index, 0x00RRGGBB] */
+ULONG colour_table[] = {
+    32,   0,         /* 32 colours starting at index 0 */
+    0x00FF0000,      /* COLOR00 = red */
+    0x0000FF00,      /* COLOR01 = green */
+    /* ... */
+    ~0UL             /* terminator */
+};
+LoadRGB32(vp, colour_table);
+```
+
+## References
+
+- ADCD 2.1 Hardware Manual — AGA register appendix
+- NDK39: `hardware/custom.h`, `graphics/view.h`
+- Commodore A1200/A4000 Technical Reference Manuals
+- AmigaMail Vol. 2 — AGA colour programming