emu8910

This repository contains a Typescript implementation of General Instrument's A-3-8910 PSG (programmable sound generator) in less than 1K lines and without any magic constants!

It implements most of the PSG's original registers.

The offical datasheet for the PSG can be found here.

Online Player/Emulator by DrSnuggles
AYSir [source]

Sound output is achieved in the browser through an AudioContext() hook.
This emulator also adds interrupt support (with variable frequency) for updating the PSG's registers.

Note: FIR LPF data is generated procedurally.

Compile with tsc emu8910.ts.

To use simply create a PSG49 object as follows:

var emu8910 = new PSG49(YM_CLOCK_ZX, 50);

Which sets the default clock speed (1.75 MHz) and interrupt frequency (50 Hz).

This exposes a a PSG register file in the emu8910.register object:

emu8910.register.A_FINE
emu8910.register.A_COARSE
emu8910.register.B_FINE
emu8910.register.B_COARSE
emu8910.register.C_FINE
emu8910.register.C_COARSE
emu8910.register.NOISE_PERIOD
emu8910.register.MIXER
emu8910.register.A_VOL
emu8910.register.B_VOL
emu8910.register.C_VOL
emu8910.register.ENV_FINE
emu8910.register.ENV_COARSE
emu8910.register.ENV_SHAPE

The register file is then used to control the PSG or extract state information.

To play a FYM module:

song = new FYMReader(<BUFFER>);
emu8910.interrupt.routine = <ISR_FUNC>
emu8910.clock.frequency = song.getClockRate()
emu8910.interrupt.frequency = song.getFrameRate()

Note: You can download modules from https://ftp.modland.com/pub/modules/

This sets the ISR (Interrupt Service Routine) function, clock and interrupt frequency for a specific module.

To stop playback:

emu8910.driver.device.suspend()
emu8910.interrupt.frequency = 0

To resume:

emu8910.driver.device.resume()
emu8910.interrupt.frequency = song.getFrameRate()

Note: You can access the emulator's internal register file with emu8910.register.

These registers need to be updated at the frequency of the ISR.

Files:

• src/emu8910.ts - core emulator implementation.
• fym.js - FYM (Fast YM) format parser.
• parser.js - PSG register parser.
• index.html - HTML boilerplate.

To run demo start web server: python -m http.server 8000 and navigate to index.html.

Note: Click anywhere on the page to start audio output.

Signature

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| Lunar RF Labs                         |
| https://lunar.sh                      |
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| RF Research Laboratories              |
| Copyright (C) 2022-2024               |
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