Crate oplon 

oplon

A no_std, integer-only OPL2 / OPL3 (Yamaha YM3812 / YMF262) FM synthesis core, with a clean-room ROM set generated entirely at compile time (no float, no hand-pasted magic tables).

The chip powers up as an OPL2 (9 channels, mono, waveforms 0-3) and becomes a full OPL3 — 18 channels, stereo panning, waveforms 4-7 — once OPL3 mode is enabled (port-1 register 0x05, or Opl2::set_opl3_enabled), exactly like the real hardware. So OPL2 code paths are unchanged while OPL3 streams get the extra features (including 4-operator mode).

Properties

• no_std, zero heap allocation, zero floating-point, fully deterministic.
• Up to 18 two-operator FM channels (two banks) + the OPL rhythm mode.
• Register-level interface (Opl2::write_reg) and a structured note/patch interface (Opl2::set_patch, Opl2::key_on, …).
• Operators run at the chip’s native rate (clock / 72); the output is 4-point-cubic-resampled to your sample rate, so the chip’s own aliasing matches the silicon.
• Log-sine / exp ROMs and the envelope-increment table are generated from their defining hardware formulas in integer const fn, verified within ±1 LSB of the canonical values.

Minimal usage (register level — what a VGM/DRO player needs)

use oplon::Opl2;

let mut opl = Opl2::new(44_100); // output sample rate
// Program a simple carrier tone on channel 0 (raw AdLib registers):
opl.write_reg(0x20, 0x01); // op0 mult = 1
opl.write_reg(0x40, 0x00); // op0 total level = loud
opl.write_reg(0x60, 0xF0); // op0 fast attack
opl.write_reg(0x80, 0x00); // op0 sustain/release
opl.write_reg(0xA0, 0x98); // F-number low
opl.write_reg(0xB0, 0x31); // key-on + block 4 + F-number high
for _ in 0..44_100 {
    let (left, right): (i32, i32) = opl.render_frame();
    // feed `left`/`right` to your DAC or audio buffer
    let _ = (left, right);
}

Scope

2-operator voices on both register banks (18 channels), OPL3 stereo panning (register 0xC0 bits 4/5), the 8 OPL3 waveforms, and 4-operator linking (port-1 register 0x04, the four connection algorithms).

Clean-room & attribution

This crate is MIT-licensed. The OPL emulators it is validated against are not: Schism Tracker’s player/fmopl3.c (a ymf262 core) is GPL-2.0+, © Jarek Burczynski, and Nuked-OPL3 is LGPL. No code or data table is copied from either. Every constant here is independently generated from the documented hardware behaviour and integer math: the log-sin/exp ROMs from their defining formulas, the envelope increments from the documented (4+lo)·2^rate_hi rate law, the tremolo/vibrato LFOs from their documented triangle/8-step shapes, and the MUL/KSL/key-scale values from the Yamaha YM3812/YMF262 datasheet. Those references are consulted only as behavioural references (to know what the silicon does); the implementation — structure, code and tables — is original.

Structs

ChannelPatch

A full 2-operator channel patch.

OpPatch

One operator’s decoded patch fields.

Opl2

An OPL2/OPL3 chip: up to 18 two-operator channels summed to stereo.

Opl3

Alias for Opl2: the same chip type, which becomes a full OPL3 (18 channels, stereo, waveforms 4-7) once Opl2::set_opl3_enabled — or the port-1 0x05 register — turns OPL3 mode on. An OPL2/OPL3 chip: up to 18 two-operator channels summed to stereo.

Constants

OPL2_CHANNELS

Number of 2-operator channels on an OPL2 (YM3812).

OPL3_CHANNELS

Number of 2-operator channels on an OPL3 (YMF262): two banks of 9.

OPL_NATIVE_RATE

Native OPL sample rate for the canonical clock (YM3812_CLOCK / 72, equal to the OPL3 YMF262_CLOCK / 288). F-numbers are computed against the chip’s native rate; the resampler then converts to the caller’s output rate.

YM3812_CLOCK

The canonical YM3812 (OPL2) master clock (Hz). The native operator rate is clock / 72.

YMF262_CLOCK

The canonical YMF262 (OPL3) master clock (Hz), 4× the OPL2 clock. The native operator rate is clock / 288 — the same 49716 Hz, since the YMF262 has 4× the operators to service per sample.