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/ecs_a600_a3000/productivity_modes.md

@@ -0,0 +1,97 @@
+[← Home](../../README.md) · [Hardware](../README.md) · [ECS](README.md)
+
+# ECS Productivity & Multiscan Display Modes
+
+## Overview
+
+ECS introduces **BEAMCON0** which allows the Amiga to produce non-standard display timings. The most useful are **productivity mode** (~28 kHz / 31 kHz horizontal) and **multiscan mode**, which provide flicker-free, high-resolution displays compatible with standard SVGA monitors.
+
+These modes are available on A3000 and some A2000/A600 configurations with a multisync monitor.
+
+## Standard OCS Timings (for reference)
+
+| Mode | H rate | V rate | Resolution |
+|---|---|---|---|
+| PAL LORES | 15.625 kHz | 50 Hz | 320×256 |
+| PAL HIRES | 15.625 kHz | 50 Hz | 640×256 |
+| NTSC LORES | 15.720 kHz | 60 Hz | 320×200 |
+| NTSC HIRES | 15.720 kHz | 60 Hz | 640×200 |
+| PAL interlace | 15.625 kHz | 50 Hz (25 Hz/field) | 320×512 / 640×512 |
+
+## ECS Multiscan Modes
+
+| Mode | H rate | V rate | Resolution | BEAMCON0 |
+|---|---|---|---|---|
+| Productivity | ~28.6 kHz | 57 Hz | 640×480 | $0A00 |
+| Super72 | ~28.6 kHz | 72 Hz | 800×600 (approx) | varies |
+| DblPAL | 31.25 kHz | 50 Hz | 640×512 | custom |
+| DblNTSC | 31.47 kHz | 60 Hz | 640×400 | custom |
+| VGA-like | 31.47 kHz | 60 Hz | 640×480 | custom |
+
+## Programming Productivity Mode
+
+Productivity mode on the A3000 (PAL, 640×480):
+
+```asm
+; Set BEAMCON0 for variable beam timing
+move.w  #$0A00, $DFF1DC    ; VARBEAMEN | VARVSYEN
+
+; Program horizontal total, sync, blank (custom timing)
+move.w  #$71, $DFF1C0      ; HTOTAL (horizontal total - 1)
+move.w  #$0F, $DFF1C4      ; HSSTRT (H sync start)
+move.w  #$19, $DFF1C6      ; HSSTOP (H sync stop)
+move.w  #$09, $DFF1C8      ; HBSTRT (H blank start)
+move.w  #$71, $DFF1CA      ; HBSTOP (H blank stop)
+
+; Vertical timing
+move.w  #$0242, $DFF1E0    ; VTOTAL
+move.w  #$0015, $DFF1E6    ; VSSTRT
+move.w  #$001D, $DFF1E8    ; VSSTOP
+```
+
+> [!NOTE]
+> The exact register values depend on the target monitor's sync requirements. The A3000's monitor (1084S or Commodore 1950) has a specific timing window. Always consult the monitor's datasheet.
+
+## OS Support: ScreenModes
+
+AmigaOS 3.1 integrates ECS productivity modes through the **screenmode** system:
+
+```c
+#include <graphics/modeid.h>
+#include <libraries/asl.h>
+
+/* Open a 640×480 productivity screen */
+struct Screen *scr = OpenScreenTags(NULL,
+    SA_DisplayID,  PRODDBL_MONITOR_ID | HIRES_KEY,
+    SA_Width,      640,
+    SA_Height,     480,
+    SA_Depth,      4,
+    TAG_DONE);
+```
+
+**Key mode IDs for ECS:**
+```c
+#define MULTISCAN_MONITOR_ID  0x00041000  /* multiscan / productivity */
+#define SUPER72_MONITOR_ID    0x00081000
+#define DBLNTSC_MONITOR_ID    0x00401000
+#define DBLPAL_MONITOR_ID     0x00421000
+```
+
+These IDs are returned by `BestModeID()` and accepted by `OpenScreen()` / `OpenScreenTags()`.
+
+## Hardware Requirements
+
+- **ECS chipset** (Super Agnus + ECS Denise) — required for BEAMCON0
+- **Multisync monitor** — standard 15 kHz PAL/NTSC monitors do not support 31 kHz
+- **A3000** — has built-in multiscan support; A2000 requires a separate scan doubler card
+
+## Flicker Fixer (A2000/A500)
+
+Some Zorro II cards (e.g., Flicker Fixer by MicroWay, Indivision ECS) scan-double the 15 kHz signal to 31 kHz for use with VGA monitors. These operate transparently — no BEAMCON0 programming needed.
+
+## References
+
+- ADCD 2.1 Hardware Manual — ECS display modes
+- AmigaMail Vol. 2 — ECS multiscan articles
+- NDK39: `graphics/modeid.h` — monitor mode IDs
+- A3000 Technical Reference Manual — display timing chapter