From 72496d2daf9efb5b62a2ab81b7d669582ee900ec Mon Sep 17 00:00:00 2001
From: Ashley Strahle <ash@jackofclubs.com.au>
Date: Fri, 3 Jul 2026 07:13:38 +0000
Subject: [PATCH] Fix MIDI clock phase: handle 0xFA START to reset tick counter
 to downbeat

---
 src/main.cpp           | 5 +++--
 src/midi_transport.cpp | 9 +++++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 5b353cc..262177d 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -27,7 +27,7 @@ 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_t last_beat = 0;
+    uint32_t last_beat = UINT32_MAX;
     uint32_t flash_start = 0;
 
     while (true) {
@@ -40,7 +40,8 @@ void midi_task(void* parameter) {
         // Calculate beat using MIDI tick count (24 ticks per beat/PPQN)
         uint32_t current_beat = tick / 24;
 
-        // Check if we've crossed a beat boundary
+        // Check if we've crossed a beat boundary.
+        // last_beat starts as UINT32_MAX so tick 0 (START) always triggers
         if (current_beat != last_beat) {
             last_beat = current_beat;
             flash_start = now;
diff --git a/src/midi_transport.cpp b/src/midi_transport.cpp
index a6fa11f..f76975a 100644
--- a/src/midi_transport.cpp
+++ b/src/midi_transport.cpp
@@ -54,8 +54,13 @@ void UsbMidiTransport::update() {
         uint8_t packet[4];
         if (usb_midi.readPacket(packet)) {
             uint8_t cin = packet[0] & 0x0F;
-            if (cin == 0x0F && packet[1] == 0xF8) {
-                midi_tick_count++;
+            if (cin == 0x0F) {
+                if (packet[1] == 0xF8) {
+                    midi_tick_count++;
+                } else if (packet[1] == 0xFA) {
+                    midi_tick_count = 0;
+                    Serial.println("[CLK] START - reset tick to 0");
+                }
                 continue;
             }