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.

11_libraries/utility.md

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+[← Home](../README.md) · [Libraries](README.md)
+
+# utility.library — TagItems, Hooks, Date Utilities
+
+## Overview
+
+`utility.library` (OS 2.0+) provides the universal tag-based parameter passing system, callback hooks, and date/time utilities used throughout AmigaOS.
+
+---
+
+## TagItem System
+
+```c
+/* utility/tagitem.h — NDK39 */
+struct TagItem {
+    ULONG ti_Tag;   /* tag identifier */
+    ULONG ti_Data;  /* tag value */
+};
+
+/* Special tag values: */
+#define TAG_DONE    0          /* end of tag list */
+#define TAG_END     TAG_DONE
+#define TAG_IGNORE  1          /* skip this tag */
+#define TAG_MORE    2          /* ti_Data = pointer to another TagItem array */
+#define TAG_SKIP    3          /* skip next ti_Data tags */
+#define TAG_USER    (1<<31)    /* user-defined tags start here */
+```
+
+### Tag Utility Functions
+
+| Function | Description |
+|---|---|
+| `FindTagItem(tag, tagList)` | Find first matching tag |
+| `GetTagData(tag, default, tagList)` | Get tag value with default |
+| `NextTagItem(&tagListPtr)` | Iterate through tags |
+| `TagInArray(tag, array)` | Check if tag is in an array |
+| `FilterTagItems(tagList, filter, logic)` | Filter tag list |
+| `CloneTagItems(tagList)` | Allocate copy of tag list |
+| `FreeTagItems(tagList)` | Free cloned tag list |
+| `MapTags(tagList, mapList, flags)` | Remap tag IDs |
+
+---
+
+## Hook System
+
+```c
+/* utility/hooks.h */
+struct Hook {
+    struct MinNode  h_MinNode;
+    ULONG         (*h_Entry)(void);   /* assembler entry point */
+    ULONG         (*h_SubEntry)(void); /* C function pointer */
+    APTR            h_Data;            /* user data */
+};
+```
+
+Convention: `h_Entry` receives `A0=hook, A2=object, A1=message`.
+
+```c
+/* Convenience macro for SAS/C and GCC: */
+ULONG myHookFunc(struct Hook *hook __asm("a0"),
+                 Object *obj __asm("a2"),
+                 APTR msg __asm("a1"))
+{
+    /* ... */
+    return 0;
+}
+
+struct Hook myHook = { {NULL}, (HOOKFUNC)myHookFunc, NULL, myData };
+```
+
+---
+
+## Date Utilities
+
+```c
+struct ClockData cd;
+Amiga2Date(seconds, &cd);  /* seconds since 1.1.1978 → date */
+ULONG secs = Date2Amiga(&cd); /* date → seconds */
+ULONG secs = CheckDate(&cd);  /* validate and convert */
+```
+
+---
+
+## References
+
+- NDK39: `utility/tagitem.h`, `utility/hooks.h`, `utility/date.h`