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Ilia Sharin 21751c0025 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.

2026-04-23 12:17:35 -04:00

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← Home · Exec Kernel

Exception and Trap Handling — M68k on AmigaOS

Overview

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.

Exception Vector Table

Vector	Address	Exception	AmigaOS Handler
0	`$000`	Reset: Initial SSP	(boot value)
1	`$004`	Reset: Initial PC	ROM entry point
2	`$008`	Bus Error	Guru Meditation / Enforcer
3	`$00C`	Address Error	Guru Meditation
4	`$010`	Illegal Instruction	Guru Meditation
5	`$014`	Zero Divide	Alert
6	`$018`	CHK Instruction	Alert
7	`$01C`	TRAPV	Alert
8	`$020`	Privilege Violation	Alert
9	`$024`	Trace	Debug (wack/BareFoot)
10	`$028`	Line-A Emulator	Unused (soft trap space)
11	`$02C`	Line-F Emulator	68040/060.library FPU emulation
12–14	`$030–$038`	Reserved	—
15	`$03C`	Uninitialised Interrupt	Alert
24	`$060`	Spurious Interrupt	—
25–31	`$064–$07C`	Auto-vector interrupts 1–7	Exec interrupt dispatcher
32–47	`$080–$0BC`	TRAP #0–#15	User-installable traps
48–63	`$0C0–$0FC`	Reserved (FPU)	68881/68882 exception handlers
64–255	`$100–$3FC`	User-defined vectors	User

TRAP Instructions — Software Interrupts

TRAP #n (n = 0–15) generates a software exception. AmigaOS uses:

TRAP	User
`TRAP #0`	exec.library `Supervisor()` — switch to supervisor mode
`TRAP #1–#14`	Available for user programs
`TRAP #15`	Remote debugger breakpoint (BareFoot/wack)

Installing an Exception Handler

/* Using exec.library SetExcept/SetTrapHandler (not recommended): */
/* Direct vector patching in supervisor mode: */

APTR OldVector;

__asm void MyTrapHandler(void)
{
    /* Save registers, examine stack frame */
    /* ... handle trap ... */
    rte
}

/* Install: */
Supervisor(function() {
    OldVector = *(APTR *)0x0B0;     /* TRAP #12 vector */
    *(APTR *)0x0B0 = MyTrapHandler;
});

Guru Meditation

When a fatal exception occurs (Bus Error, Address Error), exec.library displays:

Software Failure.   Press left mouse button to continue.
Guru Meditation #XXYYYYYY.ZZZZZZZZ

Field	Meaning
`XX`	Alert type: $00=recovery possible, $80=dead-end
`YYYYYY`	Error code (subsystem + specific error)
`ZZZZZZZZ`	Address where error occurred

Common Guru Codes

Code	Meaning
`$80000003`	Address Error (dead-end)
`$80000004`	Illegal instruction (dead-end)
`$81000005`	exec: No memory
`$82000005`	graphics: No memory
`$87000007`	trackdisk: No disk
`$04000001`	exec: Recoverable alert
`$00000001`	No memory (recoverable)

References

Motorola: MC68000 Family Reference Manual — exception processing
NDK39: exec/alerts.h — alert code definitions
RKRM: Exception chapter

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