+void disable_jtag(void) {
+// To use PORTF disable JTAG with writing JTD bit twice within four cycles.
+#if (defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__) || defined(__AVR_ATmega32U4__))
+ MCUCR |= _BV(JTD);
+ MCUCR |= _BV(JTD);
+#endif
+}
+