sb16: OPL2/OPL3 via AudioWorklet, ADPCM, MPU-401 UART, AdLib compat ports, and mixer/DSP fixes

src/browser/speaker.js

@@ -1,6 +1,6 @@
 import {
     MIXER_CHANNEL_BOTH, MIXER_CHANNEL_LEFT, MIXER_CHANNEL_RIGHT,
-    MIXER_SRC_PCSPEAKER, MIXER_SRC_DAC, MIXER_SRC_MASTER,
+    MIXER_SRC_PCSPEAKER, MIXER_SRC_DAC, MIXER_SRC_MASTER, MIXER_SRC_OPL,
 } from "../const.js";
 import { dbg_assert, dbg_log } from "../log.js";
 import { OSCILLATOR_FREQ } from "../pit.js";
@@ -18,8 +18,9 @@ const AUDIOBUFFER_MINIMUM_SAMPLING_RATE = 8000;
 /**
  * @constructor
  * @param {!BusConnector} bus
+ * @param {Object=} options
  */
-export function SpeakerAdapter(bus)
+export function SpeakerAdapter(bus, options)
 {
     if(typeof window === "undefined")
     {
@@ -46,6 +47,8 @@ export function SpeakerAdapter(bus)
 
     this.dac = new SpeakerDAC(bus, this.audio_context, this.mixer);
 
+    this.opl2 = new OPL2Source(bus, this.audio_context, this.mixer, options && options["opl2_worklet_url"]);
+
     this.pcspeaker.start();
 
     bus.register("emulator-stopped", function()
@@ -113,6 +116,20 @@ function SpeakerMixer(bus, audio_context)
     this.node_gain_left = this.audio_context.createGain();
     this.node_gain_right = this.audio_context.createGain();
 
+    // SBPro analogue output filter (mixer 0x0E bit 5, active-low).
+    // Mono cutoff ~3.2 kHz, stereo cutoff ~8 kHz; disabled = Nyquist (passthrough).
+    this.node_sbpro_filter_left = this.audio_context.createBiquadFilter();
+    this.node_sbpro_filter_right = this.audio_context.createBiquadFilter();
+    this.node_sbpro_filter_left.type = "lowpass";
+    this.node_sbpro_filter_right.type = "lowpass";
+    // Default: filter disabled — use Nyquist so the node is transparent.
+    var nyquist = this.audio_context.sampleRate / 2;
+    this.node_sbpro_filter_left.frequency.setValueAtTime(nyquist, this.audio_context.currentTime);
+    this.node_sbpro_filter_right.frequency.setValueAtTime(nyquist, this.audio_context.currentTime);
+    // Q ≈ 0.5 approximates the first-order RC slope of the real hardware filter.
+    this.node_sbpro_filter_left.Q.setValueAtTime(0.5, this.audio_context.currentTime);
+    this.node_sbpro_filter_right.Q.setValueAtTime(0.5, this.audio_context.currentTime);
+
     this.node_merger = this.audio_context.createChannelMerger(2);
 
     // Graph
@@ -122,11 +139,13 @@ function SpeakerMixer(bus, audio_context)
 
     this.node_treble_left.connect(this.node_bass_left);
     this.node_bass_left.connect(this.node_gain_left);
-    this.node_gain_left.connect(this.node_merger, 0, 0);
+    this.node_gain_left.connect(this.node_sbpro_filter_left);
+    this.node_sbpro_filter_left.connect(this.node_merger, 0, 0);
 
     this.node_treble_right.connect(this.node_bass_right);
     this.node_bass_right.connect(this.node_gain_right);
-    this.node_gain_right.connect(this.node_merger, 0, 1);
+    this.node_gain_right.connect(this.node_sbpro_filter_right);
+    this.node_sbpro_filter_right.connect(this.node_merger, 0, 1);
 
     this.node_merger.connect(this.audio_context.destination);
 
@@ -188,6 +207,16 @@ function SpeakerMixer(bus, audio_context)
     bus.register("mixer-treble-right", create_gain_handler(this.node_treble_right), this);
     bus.register("mixer-bass-left", create_gain_handler(this.node_bass_left), this);
     bus.register("mixer-bass-right", create_gain_handler(this.node_bass_right), this);
+
+    bus.register("mixer-sbpro-filter", function(data)
+    {
+        // data[0]: filter enabled (bit 5 = 0), data[1]: stereo
+        var enabled = data[0];
+        var stereo  = data[1];
+        var cutoff  = enabled ? (stereo ? 8000 : 3200) : this.audio_context.sampleRate / 2;
+        this.node_sbpro_filter_left.frequency.setValueAtTime(cutoff, this.audio_context.currentTime);
+        this.node_sbpro_filter_right.frequency.setValueAtTime(cutoff, this.audio_context.currentTime);
+    }, this);
 }
 
 /**
@@ -393,6 +422,7 @@ SpeakerMixerSource.prototype.set_volume = function(value, channel)
 SpeakerMixerSource.prototype.set_gain_hidden = function(value)
 {
     this.gain_hidden = value;
+    this.update();
 };
 
 /**
@@ -448,6 +478,56 @@ PCSpeaker.prototype.start = function()
     this.node_oscillator.start();
 };
 
+/**
+ * OPL2/OPL3 FM synthesizer source wired through the SpeakerMixer.
+ * Receives OPL register writes from SB16 via the bus and forwards
+ * them to the AudioWorklet running in opl2-worklet.js.
+ *
+ * @constructor
+ * @param {!BusConnector} bus
+ * @param {!AudioContext} audio_context
+ * @param {!SpeakerMixer} mixer
+ * @param {string=} worklet_url
+ */
+function OPL2Source(bus, audio_context, mixer, worklet_url)
+{
+    var _port = null;
+    var _queue = [];
+
+    function send(msg)
+    {
+        if(_port) _port.postMessage(msg);
+        else _queue.push(msg);
+    }
+
+    // Placeholder pass-through node; registered synchronously so mixer-volume
+    // events from mixer_full_update() find the source immediately.
+    var node_output = audio_context.createGain();
+    var mixer_connection = mixer.add_source(node_output, MIXER_SRC_OPL);
+    // OPL output amplitude is ~2/3 of full-scale PCM; scale up to match.
+    mixer_connection.set_gain_hidden(1.5);
+
+    if(window.AudioWorklet && worklet_url)
+    {
+        audio_context.audioWorklet.addModule(/** @type{string} */ (worklet_url)).then(function()
+        {
+            var node = new AudioWorkletNode(audio_context, "opl2", { outputChannelCount: [2] });
+            node.connect(node_output);
+            _port = node.port;
+            for(var i = 0; i < _queue.length; i++) _port.postMessage(_queue[i]);
+            _queue.length = 0;
+        }).catch(function(e)
+        {
+            console.error("[OPL2] AudioWorklet load failed:", e);
+        });
+    }
+
+    bus.register("opl2-reg-write", function(data)
+    {
+        send({ t: "w", r: data[0], v: data[1] });
+    }, null);
+}
+
 /**
  * @constructor
  * @param {!BusConnector} bus
@@ -809,7 +889,7 @@ function SpeakerWorkletDAC(bus, audio_context, mixer)
     // Interface
 
     this.mixer_connection = mixer.add_source(this.node_output, MIXER_SRC_DAC);
-    this.mixer_connection.set_gain_hidden(3);
+    this.mixer_connection.set_gain_hidden(1);
 
     bus.register("dac-send-data", function(data)
     {
@@ -908,7 +988,7 @@ function SpeakerBufferSourceDAC(bus, audio_context, mixer)
     this.node_output = this.node_lowpass;
 
     this.mixer_connection = mixer.add_source(this.node_output, MIXER_SRC_DAC);
-    this.mixer_connection.set_gain_hidden(3);
+    this.mixer_connection.set_gain_hidden(1);
 
     bus.register("dac-send-data", function(data)
     {

src/browser/starter.js

@@ -319,7 +319,7 @@ V86.prototype.continue_init = async function(emulator, options)
 
     if(!options.disable_speaker)
     {
-        this.speaker_adapter = new SpeakerAdapter(this.bus);
+        this.speaker_adapter = new SpeakerAdapter(this.bus, options);
     }
 
     // ugly, but required for closure compiler compilation

src/const.js

@@ -137,3 +137,4 @@ export const MIXER_CHANNEL_BOTH = 2;
 export const MIXER_SRC_MASTER = 0;
 export const MIXER_SRC_PCSPEAKER = 1;
 export const MIXER_SRC_DAC = 2;
+export const MIXER_SRC_OPL = 3;