diff --git a/include/common.h b/include/common.h
new file mode 100644
index 0000000..e96b2d8
--- /dev/null
+++ b/include/common.h
@@ -0,0 +1,9 @@
+#ifndef COMMON_H
+#define COMMON_H
+
+#define SET(X, Y)   X |= (1 << Y)
+#define CLR(X, Y)   X &= ~(1 << Y)
+#define CHK(X, Y)   X & (1 << Y)
+#define TOG(X, Y)   X ^= (1 << Y)
+
+#endif /* COMMON_H */
diff --git a/include/main.h b/include/main.h
index 58be55a..5743225 100644
--- a/include/main.h
+++ b/include/main.h
@@ -3,10 +3,19 @@
 
 #include <stdint.h>
 
-#define SET(PORT, PIN) (PORT |= (1 << PIN))
-#define CLR(PORT, PIN) (PORT &= (~(1 << PIN)))
-#define CHK(PORT, PIN) (PORT & (1 << PIN))
-#define TOG(PORT, PIN) (PORT ^= (1 << PIN))
+#ifndef F_CPU
+#define F_CPU 1000000UL
+#endif
+
+#ifdef DEBUG
+#include "debug.h"
+#endif /* DEBUG */
+
+#define SERVO_MIN       930 // (us). Go backwards
+#define SERVO_MAX       1930 // (us). Go forwards
+#define SERVO_MID       (SERVO_MIN + SERVO_MAX) / 2 // Stop
+#define PWM_PERIOD      16384 // (1000000 / F_CPU) * PRESCALER * 256) / F_CPU (us)
+#define US2TIMER0(us)   (255 * (uint32_t)us) / PWM_PERIOD
 
 void init_led(void);
 void init_pwm(void);
diff --git a/src/main.c b/src/main.c
index 1618702..04022a2 100644
--- a/src/main.c
+++ b/src/main.c
@@ -5,16 +5,6 @@
 #include "main.h"
 #include "io.h"
 
-#ifdef DEBUG
-#include "debug.h"
-#endif /* DEBUG */
-
-#define SERVO_MIN       930 // (us). Go backwards
-#define SERVO_MAX       1930 // (us). Go forwards
-#define SERVO_MID       (SERVO_MIN + SERVO_MAX) / 2 // Stop
-#define PWM_PERIOD      16384 // (1000000 / F_CPU) * PRESCALER * 256) / F_CPU (us)
-#define US2TIMER0(us)   (255 * (uint32_t)us) / PWM_PERIOD
-
 void init_pwm(void)
 {
     SERVO_DDR |= _BV(SERVO_L_PIN) | _BV(SERVO_R_PIN);