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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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File I/O — Open, Close, Read, Write, Seek

Overview

AmigaDOS file I/O is synchronous from the caller's perspective. All functions use BPTR file handles and communicate errors via IoErr().

Core Functions

LVO	Function	Registers	Returns
−30	`Open(name, mode)`	D1=name, D2=mode	D0=BPTR handle (0=fail)
−36	`Close(fh)`	D1=handle	D0=BOOL
−42	`Read(fh, buf, len)`	D1=handle, D2=buf, D3=len	D0=actual bytes (−1=error)
−48	`Write(fh, buf, len)`	D1=handle, D2=buf, D3=len	D0=actual bytes (−1=error)
−66	`Seek(fh, pos, mode)`	D1=handle, D2=pos, D3=mode	D0=old position (−1=error)

Access Modes

/* dos/dos.h — NDK39 */
#define MODE_READWRITE  1004   /* open existing, read+write */
#define MODE_OLDFILE    1005   /* open existing, read only */
#define MODE_NEWFILE    1006   /* create new (truncate if exists) */

Seek Modes

#define OFFSET_BEGINNING  -1   /* from start of file */
#define OFFSET_CURRENT     0   /* from current position */
#define OFFSET_END         1   /* from end of file */

File Handle (BPTR)

The returned handle is a BPTR to a struct FileHandle:

struct FileHandle {
    struct Message *fh_Link;
    struct MsgPort *fh_Interactive; /* non-NULL if console */
    struct MsgPort *fh_Type;       /* handler process port */
    BPTR   fh_Buf;                 /* I/O buffer (BPTR) */
    LONG   fh_Pos;                 /* current position in buffer */
    LONG   fh_End;                 /* end of valid data in buffer */
    LONG   fh_Funcs;               /* unused */
    LONG   fh_Func2;               /* unused */
    LONG   fh_Func3;               /* unused */
    LONG   fh_Args;                /* packet args */
    BPTR   fh_Arg2;
};

To access as a C pointer: struct FileHandle *fh = BADDR(handle);

Usage Example

BPTR fh = Open("RAM:test.txt", MODE_NEWFILE);
if (fh) {
    Write(fh, "Hello Amiga\n", 12);
    Close(fh);
}

fh = Open("RAM:test.txt", MODE_OLDFILE);
if (fh) {
    UBYTE buf[64];
    LONG n = Read(fh, buf, sizeof(buf));
    if (n > 0) Write(Output(), buf, n);  /* echo to stdout */
    Close(fh);
} else {
    PrintFault(IoErr(), "Open failed");
}

Error Checking

LONG err = IoErr();   /* LVO −66 — returns last DOS error code */
/* Common codes: */
#define ERROR_OBJECT_NOT_FOUND    205
#define ERROR_OBJECT_EXISTS       203
#define ERROR_DISK_FULL           221
#define ERROR_SEEK_ERROR          219

References

NDK39: dos/dos.h, dos/dosextens.h
07_dos/error_handling.md — full error code list
ADCD 2.1: Open, Close, Read, Write, Seek

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