заменила функции на макросы

cores/arduino/HardwareSerial.h

@@ -100,7 +100,7 @@ class HardwareSerial : public Stream
     using Print::write; // pull in write(str)
     operator bool() { return isInited; }
 
-    void rx_complete_irq(void) __attribute__((optimize("O3")));
+    inline void rx_complete_irq(void) __attribute__((always_inline, optimize("O3")));
 };
 
 extern HardwareSerial Serial;