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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.
106 lines
3.1 KiB
Markdown
106 lines
3.1 KiB
Markdown
[← Home](../README.md) · [Exec Kernel](README.md)
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# Exception and Trap Handling — M68k on AmigaOS
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## Overview
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The M68k CPU provides a **256-entry exception vector table** starting at address `$000000`. AmigaOS manages these vectors through `exec.library`, allowing both the OS and user code to install handlers for hardware interrupts, bus errors, and software traps.
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---
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## Exception Vector Table
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| Vector | Address | Exception | AmigaOS Handler |
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|---|---|---|---|
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| 0 | `$000` | Reset: Initial SSP | (boot value) |
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| 1 | `$004` | Reset: Initial PC | ROM entry point |
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| 2 | `$008` | Bus Error | Guru Meditation / Enforcer |
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| 3 | `$00C` | Address Error | Guru Meditation |
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| 4 | `$010` | Illegal Instruction | Guru Meditation |
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| 5 | `$014` | Zero Divide | Alert |
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| 6 | `$018` | CHK Instruction | Alert |
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| 7 | `$01C` | TRAPV | Alert |
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| 8 | `$020` | Privilege Violation | Alert |
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| 9 | `$024` | Trace | Debug (wack/BareFoot) |
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| 10 | `$028` | Line-A Emulator | Unused (soft trap space) |
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| 11 | `$02C` | Line-F Emulator | 68040/060.library FPU emulation |
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| 12–14 | `$030–$038` | Reserved | — |
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| 15 | `$03C` | Uninitialised Interrupt | Alert |
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| 24 | `$060` | Spurious Interrupt | — |
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| 25–31 | `$064–$07C` | Auto-vector interrupts 1–7 | Exec interrupt dispatcher |
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| 32–47 | `$080–$0BC` | TRAP #0–#15 | User-installable traps |
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| 48–63 | `$0C0–$0FC` | Reserved (FPU) | 68881/68882 exception handlers |
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| 64–255 | `$100–$3FC` | User-defined vectors | User |
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---
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## TRAP Instructions — Software Interrupts
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`TRAP #n` (n = 0–15) generates a software exception. AmigaOS uses:
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| TRAP | User |
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|---|---|
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| `TRAP #0` | exec.library `Supervisor()` — switch to supervisor mode |
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| `TRAP #1–#14` | Available for user programs |
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| `TRAP #15` | Remote debugger breakpoint (BareFoot/wack) |
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---
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## Installing an Exception Handler
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```c
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/* Using exec.library SetExcept/SetTrapHandler (not recommended): */
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/* Direct vector patching in supervisor mode: */
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APTR OldVector;
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__asm void MyTrapHandler(void)
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{
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/* Save registers, examine stack frame */
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/* ... handle trap ... */
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rte
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}
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/* Install: */
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Supervisor(function() {
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OldVector = *(APTR *)0x0B0; /* TRAP #12 vector */
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*(APTR *)0x0B0 = MyTrapHandler;
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});
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```
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---
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## Guru Meditation
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When a fatal exception occurs (Bus Error, Address Error), exec.library displays:
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```
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Software Failure. Press left mouse button to continue.
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Guru Meditation #XXYYYYYY.ZZZZZZZZ
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```
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| Field | Meaning |
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|---|---|
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| `XX` | Alert type: $00=recovery possible, $80=dead-end |
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| `YYYYYY` | Error code (subsystem + specific error) |
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| `ZZZZZZZZ` | Address where error occurred |
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### Common Guru Codes
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| Code | Meaning |
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|---|---|
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| `$80000003` | Address Error (dead-end) |
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| `$80000004` | Illegal instruction (dead-end) |
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| `$81000005` | exec: No memory |
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| `$82000005` | graphics: No memory |
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| `$87000007` | trackdisk: No disk |
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| `$04000001` | exec: Recoverable alert |
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| `$00000001` | No memory (recoverable) |
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---
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## References
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- Motorola: *MC68000 Family Reference Manual* — exception processing
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- NDK39: `exec/alerts.h` — alert code definitions
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- RKRM: Exception chapter
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