mirror of https://github.com/alfishe/amiga-bootcamp.git synced 2026-06-13 00:26:28 +00:00

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 · Devices

audio.device — DMA Audio Channels

Overview

audio.device provides access to the Amiga's 4 DMA audio channels. Each channel plays 8-bit PCM samples from Chip RAM at programmable rates.

Channel Allocation

UBYTE allocationMap[] = { 1, 2, 4, 8 }; /* channel masks */
struct IOAudio *aio = (struct IOAudio *)
    CreateIORequest(port, sizeof(struct IOAudio));
aio->ioa_Request.io_Message.mn_Node.ln_Pri = 0;
aio->ioa_Data    = allocationMap;
aio->ioa_Length  = sizeof(allocationMap);
OpenDevice("audio.device", 0, (struct IORequest *)aio, 0);
/* aio->ioa_AllocKey = allocation key for this channel */

Playing a Sample

aio->ioa_Request.io_Command = CMD_WRITE;
aio->ioa_Request.io_Flags   = ADIOF_PERVOL;
aio->ioa_Data    = sampleData;    /* MUST be in Chip RAM */
aio->ioa_Length  = sampleLength;  /* in bytes */
aio->ioa_Period  = 428;           /* ~8287 Hz (PAL) */
aio->ioa_Volume  = 64;           /* 0–64 */
aio->ioa_Cycles  = 1;            /* 0 = loop forever */
BeginIO((struct IORequest *)aio);

Period Calculation

Period = clock_constant / desired_frequency
PAL:  clock = 3546895 Hz → Period = 3546895 / freq
NTSC: clock = 3579545 Hz → Period = 3579545 / freq

Frequency	Period (PAL)
8287 Hz	428
11025 Hz	322
22050 Hz	161
28867 Hz	124 (minimum safe)

Channel Registers

Channel	Address	Description
0	`$DFF0A0`	AUD0 (left)
1	`$DFF0B0`	AUD1 (right)
2	`$DFF0C0`	AUD2 (right)
3	`$DFF0D0`	AUD3 (left)

Each channel: pointer (PTH/PTL), length (LEN), period (PER), volume (VOL).

References

NDK39: devices/audio.h
HRM: audio DMA chapter

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