Fix IntervalTimer on Teensy 3.5

teensy3/IntervalTimer.cpp

@@ -50,6 +50,7 @@ bool IntervalTimer::beginCycles(void (*funct)(), uint32_t cycles)
 		channel->TFLG = 1;
 	} else {
 		SIM_SCGC6 |= SIM_SCGC6_PIT;
+		__asm__ volatile("nop"); // solves timing problem on Teensy 3.5
 		PIT_MCR = 1;
 		channel = KINETISK_PIT_CHANNELS;
 		while (1) {