updated to use defines used in makefile or fallback to inline

src/avr_usart.h

@@ -17,9 +17,18 @@
  * AVR D1 --> AT-09 RX
  * AVR D2 --> AT-09 State
  */
-#define FOSC        1000000UL
-#define BLE_BAUD    4800 
-#define BT_UBRR     ((FOSC)/(BLE_BAUD*16UL)-1)
+
+
+//F_CPU and BAUD should be defined with -D when compiling the code.
+#ifndef F_CPU
+    #define F_CPU   1000000UL
+#endif
+
+#ifndef BUAD
+    #define BAUD    4800 
+#endif
+
+#define F_UBRR     ((F_CPU)/(BAUD*16UL)-1)
 
 #define TX_PIN      PIND1
 #define TX_DDR      DDD1