Emulator

.gitignore

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+noicesynth_linux
+miniaudio.h

EMULATOR.md

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+# NoiceSynth Linux Emulator
+
+This folder contains a Linux-based prototype for the NoiceSynth engine. It allows you to develop and visualize the DSP code on a desktop computer before deploying it to the RP2040 hardware.
+
+## Architecture
+
+*   **Engine (`synth_engine.cpp`):** The exact same C++ code used on the microcontroller. It uses fixed-point math (or integer-based phase accumulation) to generate audio.
+*   **Host (`main.cpp`):** A Linux wrapper that uses:
+    *   **Miniaudio:** For cross-platform audio output.
+    *   **SDL2:** For real-time oscilloscope visualization.
+
+## Quick Start (Distrobox)
+
+If you don't want to install dependencies manually, use the included script. It creates a lightweight container, installs the tools, and compiles the project.
+
+1.  Ensure you have `distrobox` and a container engine (Docker or Podman) installed.
+2.  Run the build script:
+    ```bash
+    ./compile_with_distrobox.sh
+    ```
+3.  Run the synthesizer:
+    ```bash
+    ./noicesynth_linux
+    ```
+
+## Manual Build
+
+If you prefer to build directly on your host machine:
+
+1.  **Install Dependencies:**
+    *   **Debian/Ubuntu:** `sudo apt install build-essential libsdl2-dev wget`
+    *   **Fedora:** `sudo dnf install gcc-c++ SDL2-devel wget`
+    *   **Arch:** `sudo pacman -S base-devel sdl2 wget`
+
+2.  **Download Miniaudio:**
+    ```bash
+    wget https://raw.githubusercontent.com/mackron/miniaudio/master/miniaudio.h
+    ```
+
+3.  **Compile:**
+    ```bash
+    make
+    ```

Makefile

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+# Compiler and flags
+CXX = g++
+CXXFLAGS = -std=c++17 -Wall -Wextra -I. $(shell sdl2-config --cflags)
+LDFLAGS = -ldl -lm -lpthread $(shell sdl2-config --libs)
+
+# Source files
+SRCS = main.cpp synth_engine.cpp
+
+# Output binary
+TARGET = noicesynth_linux
+
+all: $(TARGET)
+
+$(TARGET): $(SRCS)
+	$(CXX) $(CXXFLAGS) -o $(TARGET) $(SRCS) $(LDFLAGS)
+
+clean:
+	rm -f $(TARGET)

compile_with_distrobox.sh

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+#!/bin/bash
+set -e
+
+# Configuration
+CONTAINER_NAME="noicesynth-builder"
+IMAGE="archlinux:latest"
+
+# 1. Check for Distrobox
+if ! command -v distrobox &> /dev/null; then
+    echo "Error: distrobox is not installed on your system."
+    exit 1
+fi
+
+# 2. Create Container (if it doesn't exist)
+# We use Arch Linux for easy access to latest toolchains and SDL2
+if ! distrobox list | grep -q "$CONTAINER_NAME"; then
+    echo "Creating container '$CONTAINER_NAME'..."
+    distrobox create --image "$IMAGE" --name "$CONTAINER_NAME" --yes
+fi
+
+# 3. Execute Build Inside Container
+PROJECT_DIR=$(pwd)
+echo "Entering container to build..."
+distrobox enter "$CONTAINER_NAME" --additional-flags "--workdir $PROJECT_DIR" -- sh -c '
+    set -e # Ensure script exits on error inside the container too
+    # A. Install Dependencies (only if missing)
+    # We check for sdl2-config and wget to see if dev tools are present
+    if ! command -v sdl2-config &> /dev/null || ! command -v wget &> /dev/null; then
+        echo "Installing compiler and libraries..."
+        sudo pacman -Syu --noconfirm base-devel sdl2 wget
+    fi
+
+    # B. Download miniaudio.h (if missing)
+    if [ ! -f miniaudio.h ]; then
+        echo "Downloading miniaudio.h..."
+        wget https://raw.githubusercontent.com/mackron/miniaudio/master/miniaudio.h
+    fi
+
+    # C. Compile
+    echo "Compiling Project..."
+    make
+'
+
+echo "Build Success! Run ./noicesynth_linux to start the synth."

main.cpp

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+#define MINIAUDIO_IMPLEMENTATION
+#include "miniaudio.h"
+#include <SDL2/SDL.h>
+#include <vector>
+#include <atomic>
+#include "synth_engine.h" // Include our portable engine
+
+#include <stdio.h>
+
+// --- Configuration ---
+const uint32_t SAMPLE_RATE = 44100;
+const uint32_t CHANNELS = 1; // Mono
+const int WINDOW_WIDTH = 800;
+const int WINDOW_HEIGHT = 600;
+
+// --- Visualization Buffer ---
+const size_t VIS_BUFFER_SIZE = 8192;
+std::vector<int16_t> vis_buffer(VIS_BUFFER_SIZE, 0);
+std::atomic<size_t> vis_write_index{0};
+
+// --- Global Synth Engine Instance ---
+// The audio callback needs access to our synth, so we make it global.
+SynthEngine engine(SAMPLE_RATE);
+
+/**
+ * @brief The audio callback function that miniaudio will call.
+ *
+ * This function acts as the bridge between the audio driver and our synth engine.
+ * It asks the engine to fill the audio buffer provided by the driver.
+ */
+void data_callback(ma_device* pDevice, void* pOutput, const void* pInput, ma_uint32 frameCount) {
+    (void)pDevice; // Unused
+    (void)pInput;  // Unused
+
+    // Cast the output buffer to the format our engine expects (int16_t).
+    int16_t* pOutputS16 = (int16_t*)pOutput;
+
+    // Tell our engine to process `frameCount` samples and fill the buffer.
+    engine.process(pOutputS16, frameCount);
+
+    // Copy to visualization buffer
+    size_t idx = vis_write_index.load(std::memory_order_relaxed);
+    for (ma_uint32 i = 0; i < frameCount; ++i) {
+        vis_buffer[idx] = pOutputS16[i];
+        idx = (idx + 1) % VIS_BUFFER_SIZE;
+    }
+    vis_write_index.store(idx, std::memory_order_relaxed);
+}
+
+int main(int argc, char* argv[]) {
+    (void)argc; (void)argv;
+
+    // --- Init SDL ---
+    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
+        printf("SDL could not initialize! SDL_Error: %s\n", SDL_GetError());
+        return -1;
+    }
+
+    SDL_Window* window = SDL_CreateWindow("NoiceSynth Scope", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, WINDOW_WIDTH, WINDOW_HEIGHT, SDL_WINDOW_SHOWN);
+    if (!window) return -1;
+
+    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
+    if (!renderer) return -1;
+
+    ma_device_config config = ma_device_config_init(ma_device_type_playback);
+    config.playback.format   = ma_format_s16; // Must match our engine's output format
+    config.playback.channels = CHANNELS;
+    config.sampleRate        = SAMPLE_RATE;
+    config.dataCallback      = data_callback;
+
+    ma_device device;
+    if (ma_device_init(NULL, &config, &device) != MA_SUCCESS) {
+        printf("Failed to initialize playback device.\n");
+        SDL_DestroyRenderer(renderer);
+        SDL_DestroyWindow(window);
+        SDL_Quit();
+        return -1;
+    }
+
+    printf("Device Name: %s\n", device.playback.name);
+
+    ma_device_start(&device);
+
+    // --- Main Loop ---
+    bool quit = false;
+    SDL_Event e;
+
+    while (!quit) {
+        while (SDL_PollEvent(&e) != 0) {
+            if (e.type == SDL_QUIT) {
+                quit = true;
+            }
+        }
+
+        // Clear screen
+        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
+        SDL_RenderClear(renderer);
+
+        // Draw Waveform
+        SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255); // Green
+
+        // Determine read position (snapshot atomic write index)
+        size_t write_idx = vis_write_index.load(std::memory_order_relaxed);
+        
+        // Find trigger (zero crossing) to stabilize the display
+        // Look back from write_idx to find a stable point
+        size_t search_start_offset = 2000; 
+        size_t read_idx = (write_idx + VIS_BUFFER_SIZE - search_start_offset) % VIS_BUFFER_SIZE;
+        
+        // Simple trigger search: find crossing from negative to positive
+        for (size_t i = 0; i < 1000; ++i) {
+            int16_t s1 = vis_buffer[read_idx];
+            size_t next_idx = (read_idx + 1) % VIS_BUFFER_SIZE;
+            int16_t s2 = vis_buffer[next_idx];
+            
+            if (s1 <= 0 && s2 > 0) {
+                read_idx = next_idx; // Found trigger
+                break;
+            }
+            read_idx = next_idx;
+        }
+
+        // Draw points
+        int prev_x = 0;
+        int prev_y = WINDOW_HEIGHT / 2;
+        
+        for (int x = 0; x < WINDOW_WIDTH; ++x) {
+            int16_t sample = vis_buffer[read_idx];
+            read_idx = (read_idx + 1) % VIS_BUFFER_SIZE;
+
+            // Map 16-bit sample (-32768 to 32767) to screen height
+            // Invert Y because screen Y grows downwards
+            int y = WINDOW_HEIGHT / 2 - (sample * (WINDOW_HEIGHT / 2) / 32768);
+            
+            if (x > 0) {
+                SDL_RenderDrawLine(renderer, prev_x, prev_y, x, y);
+            }
+            prev_x = x;
+            prev_y = y;
+        }
+
+        SDL_RenderPresent(renderer);
+    }
+
+    ma_device_uninit(&device);
+    SDL_DestroyRenderer(renderer);
+    SDL_DestroyWindow(window);
+    SDL_Quit();
+    return 0;
+}

synth_engine.cpp

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+#include "synth_engine.h"
+
+SynthEngine::SynthEngine(uint32_t sampleRate)
+    : _sampleRate(sampleRate),
+      _phase(0),
+      _increment(0)
+{
+    // Initialize with a default frequency
+    setFrequency(440.0f);
+}
+
+void SynthEngine::setFrequency(float freq) {
+    // Calculate the phase increment for a given frequency.
+    // The phase accumulator is a 32-bit unsigned integer (0 to 2^32 - 1).
+    // One full cycle of the accumulator represents one cycle of the waveform.
+    // increment = (frequency * 2^32) / sampleRate
+    // We use a 64-bit intermediate calculation to prevent overflow.
+    _increment = static_cast<uint32_t>((static_cast<uint64_t>(freq) << 32) / _sampleRate);
+}
+
+void SynthEngine::process(int16_t* buffer, uint32_t numFrames) {
+    for (uint32_t i = 0; i < numFrames; ++i) {
+        // 1. Advance the phase. Integer overflow automatically wraps it,
+        //    which is exactly what we want for a continuous oscillator.
+        _phase += _increment;
+
+        // 2. Generate the sample. For a sawtooth wave, the sample value is
+        //    directly proportional to the phase. We take the top 16 bits
+        //    of the 32-bit phase accumulator to get a signed 16-bit sample.
+        int16_t sample = static_cast<int16_t>(_phase >> 16);
+
+        // 3. Write the sample to the buffer.
+        buffer[i] = sample;
+    }
+}

synth_engine.h

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+#ifndef SYNTH_ENGINE_H
+#define SYNTH_ENGINE_H
+
+#include <stdint.h>
+
+/**
+ * @class SynthEngine
+ * @brief A portable, platform-agnostic synthesizer engine.
+ *
+ * This class contains the core digital signal processing (DSP) logic.
+ * It has no dependencies on any specific hardware, OS, or audio API.
+ * It works by filling a provided buffer with 16-bit signed audio samples.
+ *
+ * The oscillator uses a 32-bit unsigned integer as a phase accumulator,
+ * which is highly efficient and avoids floating-point math in the audio loop,
+ * making it ideal for the RP2040.
+ */
+class SynthEngine {
+public:
+    /**
+     * @brief Constructs the synthesizer engine.
+     * @param sampleRate The audio sample rate in Hz (e.g., 44100).
+     */
+    SynthEngine(uint32_t sampleRate);
+
+    /**
+     * @brief Fills a buffer with audio samples. This is the main audio callback.
+     * @param buffer Pointer to the output buffer to be filled.
+     * @param numFrames The number of audio frames (samples) to generate.
+     */
+    void process(int16_t* buffer, uint32_t numFrames);
+
+    /**
+     * @brief Sets the frequency of the oscillator.
+     * @param freq The frequency in Hz.
+     */
+    void setFrequency(float freq);
+
+private:
+    uint32_t _sampleRate;
+    uint32_t _phase;      // Phase accumulator for the oscillator.
+    uint32_t _increment;  // Phase increment per sample, determines frequency.
+};
+
+#endif // SYNTH_ENGINE_H