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.

06_exec_os/resident_modules.md

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+[← Home](../README.md) · [Exec Kernel](README.md)
+
+# Resident Modules — RomTag, RTF_AUTOINIT, FindResident
+
+## Overview
+
+AmigaOS ROM and disk-resident modules (libraries, devices, resources) identify themselves via a **RomTag** structure. At boot, exec scans the ROM and loaded segments for RomTags and initialises every module it finds.
+
+---
+
+## struct Resident (RomTag)
+
+```c
+/* exec/resident.h — NDK39 */
+struct Resident {
+    UWORD  rt_MatchWord;    /* always $4AFC — magic identifier */
+    struct Resident *rt_MatchTag; /* pointer back to this struct (self-ref) */
+    APTR   rt_EndSkip;      /* pointer past end of this module's code */
+    UBYTE  rt_Flags;        /* RTF_* flags */
+    UBYTE  rt_Version;      /* module version number */
+    UBYTE  rt_Type;         /* NT_LIBRARY, NT_DEVICE, NT_RESOURCE, ... */
+    BYTE   rt_Pri;          /* initialisation priority (higher = earlier) */
+    char  *rt_Name;         /* module name string, e.g. "dos.library" */
+    char  *rt_IdString;     /* human-readable ID, e.g. "dos.library 40.1" */
+    APTR   rt_Init;         /* init function or InitTable pointer */
+};
+```
+
+### Magic Word
+
+`rt_MatchWord = $4AFC` is the 68k opcode for `ILLEGAL` — a deliberate trap instruction chosen so that an accidental execution of a RomTag causes an immediate CPU exception rather than silent corruption.
+
+### RTF_ Flags
+
+```c
+#define RTF_AUTOINIT (1<<7)  /* use rt_Init as pointer to InitTable */
+#define RTF_SINGLETASK (1<<1) /* init runs in single-task context */
+#define RTF_COLDSTART  (1<<0) /* init on cold boot only */
+```
+
+---
+
+## RTF_AUTOINIT — Automatic Initialisation
+
+When `RTF_AUTOINIT` is set, `rt_Init` points to an **InitTable** rather than a bare function:
+
+```c
+struct InitTable {
+    ULONG  it_DataSize;   /* size of library instance struct */
+    APTR  *it_FuncTable;  /* pointer to function pointer table */
+    APTR   it_DataTable;  /* pointer to INITBYTE/INITWORD/INITLONG table */
+    APTR   it_InitRoutine;/* pointer to actual LibInit() function */
+};
+```
+
+exec uses `MakeLibrary()` to allocate the library, install the JMP table, and initialise the data, then calls `it_InitRoutine`. For most libraries, the author only needs to provide `it_FuncTable` and `it_DataTable` and `RTF_AUTOINIT` handles the rest automatically.
+
+---
+
+## Finding a Resident by Name
+
+```c
+struct Resident *res = FindResident("dos.library");   /* LVO -60 */
+if (res) {
+    printf("Found: %s v%d\n", res->rt_Name, res->rt_Version);
+}
+```
+
+`FindResident` scans `SysBase->ResModules` — the list of all RomTag pointers collected at boot.
+
+---
+
+## ROM Scan at Boot
+
+During exec initialisation, the ROM scanner walks from `$F80000` (Kickstart base) upward looking for the `$4AFC` magic word. For each match it verifies `rt_MatchTag == &rt` (self-referential pointer), confirms `rt_EndSkip` is beyond the RomTag, and adds valid entries to `ResModules`.
+
+The same scan is applied to any loaded segment when `AddResidentModule` is called.
+
+---
+
+## Writing a Minimal RomTag (Assembly)
+
+```asm
+; Minimal ROM tag for a library:
+        dc.w    $4AFC               ; rt_MatchWord
+        dc.l    _RomTag             ; rt_MatchTag (self-ref)
+        dc.l    _EndTag             ; rt_EndSkip
+        dc.b    RTF_AUTOINIT        ; rt_Flags
+        dc.b    1                   ; rt_Version
+        dc.b    NT_LIBRARY          ; rt_Type
+        dc.b    0                   ; rt_Pri
+        dc.l    _Name               ; rt_Name
+        dc.l    _IdString           ; rt_IdString
+        dc.l    _InitTable          ; rt_Init (InitTable when AUTOINIT)
+_Name:  dc.b    "mylib.library", 0
+_IdString: dc.b "mylib.library 1.0 (23.4.2026)", 13, 10, 0
+        even
+_EndTag:
+```
+
+---
+
+## References
+
+- NDK39: `exec/resident.h`, `exec/execbase.h`
+- ADCD 2.1: `FindResident`, `InitResident`, `AddResidentModule`
+- *Amiga ROM Kernel Reference Manual: Exec* — resident modules chapter