emu8910

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

The emulator allows for fine tuning of the DAC look-up table though modification of the following constants:

const DAC_DECAY = 1.3;
const DAC_SHIFT = 40;

It implements most of the PSG's original registers.

The offical datasheet for the PSG can be found here.

Online Player/Emulator by DrSnuggles
player link

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

Note: AY8910 emulators naturally generate high frequency content which must be suppressed. This is achieved with a FIR low-pass filter using a procedurally generated Blackman-Harris window.

The FIR response can be changed through modification of the following constants:

const FIR_CUTOFF = 5000; // Hz
const FIR_TAPS = 100; // N taps

Note: FIR LPF (Low-Pass Filter) 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 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 snippet sets the ISR (Interrupt Service Routine) function which read/writes to the PSG register file and sets the clock and interrupt frequency.

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:

• emu8910.js - precompiled js emulator core
• 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 clone and start web server from the root directory: python3 -m http.server 8000 and navigate to http://127.0.0.1:8000.

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

Signature

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| Lunar RF Labs                         |
| Email: root@lunar.sh                  |
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| Research Laboratories                 |
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| Copyright (C) 2022-2024               |
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