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/signals.md

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+[← Home](../README.md) · [Exec Kernel](README.md)
+
+# Signals — AllocSignal, SetSignal, Wait
+
+## Overview
+
+Signals are the lightest AmigaOS synchronization primitive. Each task has 32 signal bits (`tc_SigAlloc`). A task blocks on `Wait(mask)` until any of the specified bits are set by another task or interrupt handler calling `Signal()`.
+
+---
+
+## Signal Bit Constants
+
+```c
+/* exec/tasks.h — NDK39 */
+/* Bits 0–15: application-allocated via AllocSignal() */
+/* Bits 16–31: reserved by exec */
+
+#define SIGB_ABORT      0    /* bit 0: break signal */
+#define SIGB_CHILD      1    /* bit 1: child task signal */
+#define SIGB_BLIT       4    /* bit 4: blitter done (exec internal) */
+#define SIGB_SINGLE     4    /* alias */
+#define SIGB_INTUITION  5    /* bit 5: Intuition events (exec internal) */
+#define SIGB_DOS        8    /* bit 8: DOS signal */
+
+/* Workbench/DOS break signals (bits 12–15): */
+#define SIGBREAKB_CTRL_C  12
+#define SIGBREAKB_CTRL_D  13
+#define SIGBREAKB_CTRL_E  14
+#define SIGBREAKB_CTRL_F  15
+
+#define SIGBREAKF_CTRL_C  (1L<<SIGBREAKB_CTRL_C)  /* $1000 */
+#define SIGBREAKF_CTRL_D  (1L<<SIGBREAKB_CTRL_D)  /* $2000 */
+#define SIGBREAKF_CTRL_E  (1L<<SIGBREAKB_CTRL_E)  /* $4000 */
+#define SIGBREAKF_CTRL_F  (1L<<SIGBREAKB_CTRL_F)  /* $8000 */
+```
+
+---
+
+## Allocating and Freeing Signals
+
+```c
+/* Allocate an unused signal bit (-1 = any free bit): */
+LONG sigBit = AllocSignal(-1);   /* LVO -246 */
+if (sigBit < 0) { /* all 16 user bits in use */ }
+
+ULONG sigMask = (1L << sigBit);
+
+/* Free when done: */
+FreeSignal(sigBit);   /* LVO -252 */
+```
+
+---
+
+## Waiting for Signals
+
+```c
+/* Block until any of the listed signals arrive: */
+ULONG received = Wait(sigMask | SIGBREAKF_CTRL_C);   /* LVO -318 */
+
+if (received & SIGBREAKF_CTRL_C) {
+    /* user pressed CTRL-C */
+    cleanup_and_exit();
+}
+if (received & sigMask) {
+    /* our custom event occurred */
+}
+```
+
+`Wait()` returns only after at least one bit in the mask is set. It is equivalent to sleeping — the task is moved to `TaskWait` and no CPU is consumed.
+
+---
+
+## Sending Signals
+
+```c
+/* Signal a task from another task or interrupt handler: */
+Signal(target_task, sigMask);   /* LVO -324 */
+```
+
+`Signal()` is safe from interrupt context.
+
+---
+
+## SetSignal — Read and Clear
+
+```c
+/* Read and clear specific signal bits atomically: */
+ULONG old = SetSignal(new_bits, change_mask);   /* LVO -306 */
+/* old = previous state of all 32 signal bits */
+/* new value = (old & ~change_mask) | (new_bits & change_mask) */
+
+/* Check CTRL-C without blocking: */
+if (SetSignal(0, SIGBREAKF_CTRL_C) & SIGBREAKF_CTRL_C) {
+    /* CTRL-C was pending — now cleared */
+}
+```
+
+---
+
+## Typical Usage Pattern: Event Loop
+
+```c
+struct MsgPort *port = CreateMsgPort();
+ULONG portSig = (1L << port->mp_SigBit);
+ULONG waitMask = portSig | SIGBREAKF_CTRL_C;
+
+BOOL running = TRUE;
+while (running) {
+    ULONG sigs = Wait(waitMask);
+
+    if (sigs & SIGBREAKF_CTRL_C) {
+        running = FALSE;
+    }
+    if (sigs & portSig) {
+        struct Message *msg;
+        while ((msg = GetMsg(port)) != NULL) {
+            /* handle message */
+            ReplyMsg(msg);
+        }
+    }
+}
+DeleteMsgPort(port);
+```
+
+---
+
+## References
+
+- NDK39: `exec/tasks.h`, `exec/execbase.h`
+- ADCD 2.1: `AllocSignal`, `FreeSignal`, `Signal`, `Wait`, `SetSignal`
+- `06_exec_os/tasks_processes.md` — tc_SigAlloc, tc_SigRecvd fields
+- *Amiga ROM Kernel Reference Manual: Exec* — signals chapter