feat: multi-arch Docker (amd64+arm64) and fix LED ground check

Docker multi-arch:
- Dockerfile downloads arch-specific QEMU .so via TARGETARCH
- docker-publish.yml adds setup-qemu-action and platforms: linux/amd64,linux/arm64
- qemu-lcgamboa submodule updated (matrix build for both architectures)

LED fix:
- LEDs now require cathode wired to GND (or LOW GPIO) to light up
- Previously LEDs turned on with anode HIGH regardless of cathode connection
- Updated tests to verify anode+cathode behavior

.github/workflows/docker-publish.yml

@@ -21,6 +21,9 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
+      - name: Set up QEMU (for multi-arch builds)
+        uses: docker/setup-qemu-action@v3
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
@@ -50,6 +53,7 @@ jobs:
         with:
           context: .
           file: Dockerfile.standalone
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}

Dockerfile.standalone

@@ -1,24 +1,33 @@
 # ---- Stage 0: QEMU .so + ROM binaries ----
-# Two modes:
-#   1. Local: place files in prebuilt/qemu/ (from build-qemu.sh or manual copy)
-#   2. CI/CD: downloads from GitHub Release (requires qemu-lcgamboa repo to be public)
-# The COPY always runs; the RUN only downloads missing files.
+# Downloads arch-specific .so from GitHub Release (e.g. libqemu-xtensa-amd64.so)
+# and renames to libqemu-xtensa.so so the backend needs no changes.
+# Local prebuilt files (prebuilt/qemu/) are used if present.
 FROM ubuntu:22.04 AS qemu-provider
 
 RUN apt-get update && apt-get install -y --no-install-recommends curl ca-certificates \
     && rm -rf /var/lib/apt/lists/*
 
+ARG TARGETARCH
 ARG QEMU_RELEASE_URL=https://github.com/davidmonterocrespo24/velxio/releases/download/qemu-prebuilt
 
 # Copy the prebuilt directory (may contain .so+ROM files or just the .gitkeep)
 RUN mkdir -p /qemu
 COPY prebuilt/qemu/ /qemu/
 
-# Download any missing files from GitHub Release
+# Download arch-specific .so and arch-independent ROM files
 RUN cd /qemu \
- && for f in libqemu-xtensa.so libqemu-riscv32.so esp32-v3-rom.bin esp32-v3-rom-app.bin esp32c3-rom.bin; do \
+ && for base in libqemu-xtensa libqemu-riscv32; do \
+      f="${base}.so" ; \
       if [ ! -f "$f" ]; then \
-        echo "Downloading $f from release..." ; \
+        echo "Downloading ${base}-${TARGETARCH}.so → $f ..." ; \
+        curl -fSL -o "$f" "${QEMU_RELEASE_URL}/${base}-${TARGETARCH}.so" ; \
+      else \
+        echo "Using local $f ($(stat -c%s "$f") bytes)" ; \
+      fi ; \
+    done \
+ && for f in esp32-v3-rom.bin esp32-v3-rom-app.bin esp32c3-rom.bin; do \
+      if [ ! -f "$f" ]; then \
+        echo "Downloading $f ..." ; \
         curl -fSL -o "$f" "${QEMU_RELEASE_URL}/$f" ; \
       else \
         echo "Using local $f ($(stat -c%s "$f") bytes)" ; \

frontend/src/__tests__/simulation-parts.test.ts

@@ -120,26 +120,51 @@ describe('PartSimulationRegistry — registration', () => {
 
 // ─── LED ─────────────────────────────────────────────────────────────────────
 
-describe('LED — onPinStateChange', () => {
-  it('sets element.value = true when anode pin goes HIGH', () => {
+describe('LED — attachEvents (anode + cathode check)', () => {
+  it('LED turns on when anode HIGH and cathode wired to GND', () => {
     const logic = PartSimulationRegistry.get('led')!;
     const el = makeElement({ value: false });
-    logic.onPinStateChange!('A', true, el);
+    const sim = makeSimulator();
+    // A → GPIO pin 13, C → GND (-1)
+    logic.attachEvents!(el, sim as any, pinMap({ 'A': 13, 'C': -1 }), 'led-1');
+
+    // pinManager.onPinChange should be called for anode (pin 13)
+    const calls = sim.pinManager.onPinChange.mock.calls;
+    const anodeCall = calls.find((c: any) => c[0] === 13);
+    expect(anodeCall).toBeDefined();
+
+    // Simulate anode going HIGH
+    anodeCall![1](13, true);
     expect((el as any).value).toBe(true);
   });
 
-  it('sets element.value = false when anode pin goes LOW', () => {
+  it('LED stays off when anode HIGH but cathode not wired', () => {
     const logic = PartSimulationRegistry.get('led')!;
-    const el = makeElement({ value: true });
-    logic.onPinStateChange!('A', false, el);
+    const el = makeElement({ value: false });
+    const sim = makeSimulator();
+    // A → pin 13, C → not wired (null)
+    logic.attachEvents!(el, sim as any, pinMap({ 'A': 13 }), 'led-2');
+
+    const calls = sim.pinManager.onPinChange.mock.calls;
+    const anodeCall = calls.find((c: any) => c[0] === 13);
+    expect(anodeCall).toBeDefined();
+
+    // Simulate anode going HIGH — should NOT light up
+    anodeCall![1](13, true);
     expect((el as any).value).toBe(false);
   });
 
-  it('ignores non-anode pins (e.g. cathode K)', () => {
+  it('LED turns off when anode goes LOW', () => {
     const logic = PartSimulationRegistry.get('led')!;
     const el = makeElement({ value: false });
-    logic.onPinStateChange!('K', true, el);
-    expect((el as any).value).toBe(false); // unchanged
+    const sim = makeSimulator();
+    logic.attachEvents!(el, sim as any, pinMap({ 'A': 13, 'C': -1 }), 'led-3');
+
+    const anodeCall = sim.pinManager.onPinChange.mock.calls.find((c: any) => c[0] === 13);
+    anodeCall![1](13, true);
+    expect((el as any).value).toBe(true);
+    anodeCall![1](13, false);
+    expect((el as any).value).toBe(false);
   });
 });
 

frontend/src/simulation/parts/BasicParts.ts

@@ -125,14 +125,49 @@ PartSimulationRegistry.register('dip-switch-8', {
 });
 
 /**
- * Basic LED implementation
+ * Basic LED implementation.
+ *
+ * An LED lights up only when current can flow: anode HIGH **and** cathode
+ * connected to GND (or a LOW GPIO).  If the cathode is not wired at all the
+ * LED stays off regardless of the anode state.
  */
 PartSimulationRegistry.register('led', {
-    onPinStateChange: (pinName, state, element) => {
-        if (pinName === 'A') { // Anode
-            (element as any).value = state;
+    attachEvents: (element, simulator, getArduinoPinHelper) => {
+        const pinManager = (simulator as any).pinManager;
+        if (!pinManager) return () => {};
+
+        const el = element as any;
+        const unsubs: (() => void)[] = [];
+        let anodeHigh  = false;
+        let cathodeLow = false;
+
+        const update = () => { el.value = anodeHigh && cathodeLow; };
+
+        // Cathode pin: -1 means wired to GND (always LOW), >=0 means GPIO
+        const cathodePin = getArduinoPinHelper('C');
+        if (cathodePin === -1) {
+            // Wired to GND — always LOW
+            cathodeLow = true;
+        } else if (cathodePin !== null && cathodePin >= 0) {
+            // Wired to a GPIO — track its state
+            unsubs.push(pinManager.onPinChange(cathodePin, (_: number, state: boolean) => {
+                cathodeLow = !state; // cathode needs to be LOW for current to flow
+                update();
+            }));
         }
+        // cathodePin === null → not wired → cathodeLow stays false → LED off
+
+        // Anode pin
+        const anodePin = getArduinoPinHelper('A');
+        if (anodePin !== null && anodePin >= 0) {
+            unsubs.push(pinManager.onPinChange(anodePin, (_: number, state: boolean) => {
+                anodeHigh = state;
+                update();
+            }));
         }
+
+        return () => { unsubs.forEach(u => u()); };
+    },
 });
 
 /**

wokwi-libs/qemu-lcgamboa

@@ -1 +1 @@
-Subproject commit 4694eb508ed17d7166b51f5e62c04167f3f8cc19
+Subproject commit 092ad4333d148ac57d28035ee5ae3e8f9b819313