diff --git a/src/uClock.cpp b/src/uClock.cpp
index 9e6e12f..74d1cc8 100755
--- a/src/uClock.cpp
+++ b/src/uClock.cpp
@@ -50,9 +50,22 @@
 //
 #if defined(ARDUINO_ARCH_ESP32) || defined(ESP32)
 	hw_timer_t * _uclockTimer = NULL;
+	portMUX_TYPE _uclockTimerMux = portMUX_INITIALIZER_UNLOCKED;
 	#define TIMER_ID	0
 #endif
 
+//
+// multicore archs
+//
+#if defined(ARDUINO_ARCH_ESP32) || defined(ESP32)
+	#define ATOMIC(X) portENTER_CRITICAL_ISR(&_uclockTimerMux); X; portEXIT_CRITICAL_ISR(&_uclockTimerMux);
+//
+// singlecore archs
+//
+#else
+	#define ATOMIC(X) noInterrupts(); X; interrupts();
+#endif
+
 #if defined(ARDUINO_ARCH_AVR)
 void uclockInitTimer()
 {
@@ -73,7 +86,14 @@ void uclockInitTimer()
 	)
 }
 #else
-void uclockISR();
+
+	// forward declaration of ISR
+	#if defined(ARDUINO_ARCH_ESP32) || defined(ESP32)
+		void ARDUINO_ISR_ATTR uclockISR();
+	#else
+		void uclockISR();
+	#endif
+
 void uclockInitTimer()
 {
 	// begin at 120bpm (20833us)
@@ -501,6 +521,8 @@ volatile uint32_t _timer = 0;
 //
 #if defined(ARDUINO_ARCH_AVR)
 ISR(TIMER1_COMPA_vect)
+#elif defined(ARDUINO_ARCH_ESP32) || defined(ESP32)
+void ARDUINO_ISR_ATTR uclockISR()
 #else
 void uclockISR() 
 #endif
diff --git a/src/uClock.h b/src/uClock.h
index cee7bd6..09b7a74 100755
--- a/src/uClock.h
+++ b/src/uClock.h
@@ -54,8 +54,6 @@ namespace umodular { namespace clock {
 #define SECS_PER_HOUR (3600UL)
 #define SECS_PER_DAY  (SECS_PER_HOUR * 24L)
 
-#define ATOMIC(X) noInterrupts(); X; interrupts();
-
 class uClockClass {
 
 	private: