Pixel 6 pulses on MIDI Clock beat (0xF8) - all on Core 0

- Detect 0xF8 in midi_transport.cpp (runs on Core 0)
- Every 24th tick = beat, flash pixel 6 white
- Instant-on, quadratic fade over 80ms, restore to dim
- All FastLED calls stay on Core 0, no cross-core conflict

include/midi_transport.h

@@ -3,6 +3,8 @@
 #include <cstdint>
 #include <functional>
 
+extern volatile uint32_t midi_tick_count;
+
 struct MidiEvent {
     enum Type {
         NOTE_ON,

src/main.cpp

@@ -25,10 +25,35 @@ TaskHandle_t midi_task_handle = NULL;
 
 void midi_task(void* parameter) {
     Serial.println("[TASK] MIDI task started on core 0");
+    uint32_t last_beat = 0;
+    uint32_t flash_start = 0;
 
     while (true) {
         midi_transport.update();
         exp_pedal.update(midi_transport);
+
+        uint32_t beat = midi_tick_count / 24;
+        if (beat != last_beat) {
+            last_beat = beat;
+            flash_start = millis();
+            mux.set_led_color(6, 255, 255, 255);
+            mux.show();
+        }
+
+        if (flash_start > 0) {
+            uint32_t elapsed = millis() - flash_start;
+            if (elapsed >= 80) {
+                mux.set_led_color(6, 20, 20, 20);
+                mux.show();
+                flash_start = 0;
+            } else {
+                float b = 1.0f - (float)elapsed / 80.0f;
+                uint8_t v = (uint8_t)(255 * b * b);
+                mux.set_led_color(6, v, v, v);
+                mux.show();
+            }
+        }
+
         vTaskDelay(1);
     }
 }

src/midi_transport.cpp

@@ -2,6 +2,8 @@
 #include <Arduino.h>
 #include "Adafruit_TinyUSB.h"
 
+volatile uint32_t midi_tick_count = 0;
+
 static Adafruit_USBD_MIDI usb_midi;
 
 UsbMidiTransport::UsbMidiTransport() : initialized(false) {
@@ -51,6 +53,12 @@ void UsbMidiTransport::update() {
     while (usb_midi.available()) {
         uint8_t packet[4];
         if (usb_midi.readPacket(packet)) {
+            uint8_t cin = packet[0] & 0x0F;
+            if (cin == 0x0F) {
+                if (packet[1] == 0xF8) midi_tick_count++;
+                continue;
+            }
+
             MidiEvent event;
             parse_midi_packet(packet, 4, event);