Remove beat 1 differentiation - all beats flash white 50ms

include/midi_transport.h

@@ -3,6 +3,10 @@
 #include <cstdint>
 #include <functional>
 
+extern volatile uint32_t midi_tick_count;
+extern volatile uint16_t last_spp_position;
+extern volatile bool spp_valid;
+
 struct MidiEvent {
     enum Type {
         NOTE_ON,

src/app_task.cpp

@@ -1,6 +1,8 @@
 #include "app_task.h"
 #include <Arduino.h>
 
+extern volatile uint8_t beats_per_bar;
+
 AppTask::AppTask(LedStub* led, SwitchStub* sw, UsbMidiTransport* midi)
     : led_driver(led), switch_driver(sw), midi_transport(midi) {
     
@@ -124,6 +126,18 @@ void AppTask::process_midi_event(const MidiEvent& event) {
 }
 
 void AppTask::process_switch_event(uint8_t switch_id, bool pressed) {
+    // Time signature combo: hold pad 10 (switch 9) + press pad 1/2/3
+    if (switch_id <= 2 && switch_driver->is_pressed(9)) {
+        if (pressed) {
+            switch (switch_id) {
+                case 0: beats_per_bar = 4; Serial.println("[APP] Time sig: 4/4"); break;
+                case 1: beats_per_bar = 3; Serial.println("[APP] Time sig: 3/4"); break;
+                case 2: beats_per_bar = 6; Serial.println("[APP] Time sig: 6/4"); break;
+            }
+        }
+        return; // suppress CC in combo mode
+    }
+
     for (uint8_t i = 0; i < NUM_PADS; i++) {
         if (pad_mapping[i].physical_switch == switch_id) {
             uint8_t channel = pad_mapping[i].midi_channel;

src/main.cpp

@@ -21,14 +21,44 @@ UsbMidiTransport midi_transport;
 AppTask controller(&led_driver, &switch_driver, &midi_transport);
 ExpressionPedal exp_pedal(4);
 
+volatile uint32_t flash_latency = 55; // ms delay to compensate for Loopy Pro rendering
+volatile uint8_t beats_per_bar = 4;   // change to match your project's time signature
+
 TaskHandle_t midi_task_handle = NULL;
 
 void midi_task(void* parameter) {
     Serial.println("[TASK] MIDI task started on core 0");
     
+    // Beat timing fixes for precise beat alignment - sync to real MIDI time, not hardcoded tempo
+    // UINT32_MAX ensures tick 0 (first 0xF8 after START) triggers a flash
+    uint32_t last_beat = UINT32_MAX;
+    uint32_t flash_start = 0;
+
     while (true) {
         midi_transport.update();
         exp_pedal.update(midi_transport);
+
+        uint32_t tick = midi_tick_count;
+        uint32_t now = millis();
+
+        uint32_t current_beat = tick / 24;
+
+        if (current_beat != last_beat) {
+            last_beat = current_beat;
+            flash_start = now + flash_latency;
+            // All beats flash white
+            mux.set_led_color(6, 255, 255, 255);
+        }
+
+        if (flash_start > 0 && now >= flash_start) {
+            mux.show();
+            if (now - flash_start >= 50) {
+                mux.set_led_color(6, 20, 20, 20);
+                mux.show();
+                flash_start = 0;
+            }
+        }
+
         vTaskDelay(1);
     }
 }
@@ -89,6 +119,16 @@ void handle_serial_command(const String& cmd) {
     } else if (cmd == "exp") {
         Serial.printf("[CMD] EXP ADC=%d MIDI=%d\n",
                       exp_pedal.get_raw(), exp_pedal.get_value());
+    } else if (cmd == "latency") {
+        Serial.printf("[CMD] Current flash latency: %d ms\n", flash_latency);
+    } else if (cmd.startsWith("latency ")) {
+        int val = atoi(cmd.c_str() + 8);
+        if (val >= 0 && val <= 500) {
+            flash_latency = val;
+            Serial.printf("[CMD] Flash latency set to %d ms\n", flash_latency);
+        } else {
+            Serial.println("[CMD] Latency must be 0-500 ms");
+        }
     } else if (cmd == "usb") {
         Serial.printf("[CMD] USB mounted: %s\n", TinyUSBDevice.mounted() ? "YES" : "NO");
         Serial.printf("[CMD] USB ready: %s\n", TinyUSBDevice.ready() ? "YES" : "NO");
@@ -133,6 +173,8 @@ void handle_serial_command(const String& cmd) {
         Serial.println("  red/green/blue - solid colour");
         Serial.println("  pixel0/pixel1 - single pixel test");
         Serial.println("  exp        - expression pedal ADC/MIDI value");
+        Serial.println("  latency    - show current flash latency");
+        Serial.println("  latency N  - set flash latency to N ms (0-500)");
         Serial.println("  usb        - USB connection status and descriptor info");
         Serial.println("  gpiotest   - raw GPIO pin diagnostic");
         Serial.println("  rawled     - bit-bang WS2812 (no library)");

src/midi_transport.cpp

@@ -2,6 +2,11 @@
 #include <Arduino.h>
 #include "Adafruit_TinyUSB.h"
 
+volatile uint32_t midi_tick_count = 0;
+volatile uint16_t last_spp_position = 0;
+volatile bool spp_valid = false;
+extern volatile uint8_t beats_per_bar;
+
 static Adafruit_USBD_MIDI usb_midi;
 
 UsbMidiTransport::UsbMidiTransport() : initialized(false) {
@@ -48,9 +53,51 @@ void UsbMidiTransport::update() {
                       TinyUSBDevice.mounted() ? "YES" : "NO");
     }
 
-    while (usb_midi.available()) {
+    if (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++;
+                } else if (packet[1] == 0xFA) {
+                    if (spp_valid) {
+                        midi_tick_count = last_spp_position * 6;
+                        spp_valid = false;
+                        Serial.printf("[CLK] START at SPP=%d -> tick %d\n", last_spp_position, midi_tick_count);
+                    } else {
+                        midi_tick_count = 0xFFFFFFFF;
+                        Serial.println("[CLK] START (no SPP) - next F8 = tick 0");
+                    }
+                } else if (packet[1] == 0xFB) {
+                    // CONTINUE - same as START for our purposes
+                    if (spp_valid) {
+                        midi_tick_count = last_spp_position * 6;
+                        spp_valid = false;
+                        Serial.printf("[CLK] CONTINUE at SPP=%d -> tick %d\n", last_spp_position, midi_tick_count);
+                    } else {
+                        Serial.println("[CLK] CONTINUE (no SPP)");
+                    }
+                }
+            } else if (cin == 0x03 && packet[1] == 0xF2) {
+                // Song Position Pointer
+                uint16_t prev_spp = last_spp_position;
+                last_spp_position = (packet[3] << 7) | packet[2];
+                spp_valid = true;
+                Serial.printf("[CLK] SPP=%d\n", last_spp_position);
+
+                // Auto-detect time signature from SPP delta (sent at bar boundaries)
+                if (prev_spp > 0 && last_spp_position > prev_spp) {
+                    uint16_t delta = last_spp_position - prev_spp;
+                    if (delta >= 8 && delta <= 64 && delta % 4 == 0) {
+                        uint8_t detected = delta / 4;
+                        if (detected >= 2 && detected <= 16 && detected != beats_per_bar) {
+                            beats_per_bar = detected;
+                            Serial.printf("[CLK] Auto-detected %d/4 time from SPP delta=%d\n", detected, delta);
+                        }
+                    }
+                }
+            } else {
                 MidiEvent event;
                 parse_midi_packet(packet, 4, event);
 
@@ -71,6 +118,7 @@ void UsbMidiTransport::update() {
             }
         }
     }
+}
 
 void UsbMidiTransport::on_midi_receive(std::function<void(const MidiEvent&)> callback) {
     receive_callback = callback;