adding SYNCING clock_state for external sync

src/uClock.cpp

@@ -304,10 +304,15 @@ void uClockClass::handleExternalClock()
             break;
 
         case STARTING:
-            clock_state = STARTED;
+            clock_state = SYNCING;
             ext_clock_us = micros();
             break;
 
+        case SYNCING:
+            // set clock_mode as start and goes on to calculate the first ext_interval
+            clock_state = STARTED;
+            // no break here just go on to calculate our first ext_interval
+
         case STARTED:
             uint32_t now_clock_us = micros();
             last_interval = clock_diff(ext_clock_us, now_clock_us);

src/uClock.h

@@ -66,6 +66,7 @@ class uClockClass {
         enum ClockState {
             PAUSED = 0,
             STARTING,
+            SYNCING,
             STARTED
         };