Add SPP (Song Position Pointer) detection - uses SPP on START to set correct tick position. Add beats_per_bar (default 4) with button combo: hold 10 + press 1=4/4, 2=3/4, 3=6/4

include/midi_transport.h

@@ -4,6 +4,8 @@
 #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 {

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

@@ -22,6 +22,7 @@ AppTask controller(&led_driver, &switch_driver, &midi_transport);
 ExpressionPedal exp_pedal(4);
 
 static volatile uint32_t flash_latency = 55; // ms delay to compensate for Loopy Pro rendering
+static volatile uint8_t beats_per_bar = 4;   // change to match your project's time signature
 
 TaskHandle_t midi_task_handle = NULL;
 
@@ -45,8 +46,8 @@ void midi_task(void* parameter) {
         if (current_beat != last_beat) {
             last_beat = current_beat;
             flash_start = now + flash_latency;
-            // Beat 1 = red on current_beat % 4 == 0, others = white
+            // Beat 1 = red on current_beat % beats_per_bar == 0, others = white
-            if (current_beat % 4 == 0) {
+            if (current_beat % beats_per_bar == 0) {
                 mux.set_led_color(6, 255, 0, 0);
             } else {
                 mux.set_led_color(6, 255, 255, 255);
@@ -55,7 +56,7 @@ void midi_task(void* parameter) {
 
         if (flash_start > 0 && now >= flash_start) {
             mux.show();
-            uint32_t hold = (last_beat % 4 == 0) ? 100 : 50;
+            uint32_t hold = (last_beat % beats_per_bar == 0) ? 100 : 50;
             uint32_t elapsed = now - flash_start;
             if (elapsed >= hold) {
                 mux.set_led_color(6, 20, 20, 20);

src/midi_transport.cpp

@@ -3,6 +3,8 @@
 #include "Adafruit_TinyUSB.h"
 
 volatile uint32_t midi_tick_count = 0;
+volatile uint16_t last_spp_position = 0;
+volatile bool spp_valid = false;
 
 static Adafruit_USBD_MIDI usb_midi;
 
@@ -58,9 +60,29 @@ void UsbMidiTransport::update() {
                 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 - next F8 = tick 0");
+                        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
+                last_spp_position = (packet[3] << 7) | packet[2];
+                spp_valid = true;
+                Serial.printf("[CLK] SPP=%d\n", last_spp_position);
             } else {
                 MidiEvent event;
                 parse_midi_packet(packet, 4, event);