diff --git a/sw/airborne/arm7/sys_time_hw.h b/sw/airborne/arm7/sys_time_hw.h
index d55899d432..356d0e04b0 100644
--- a/sw/airborne/arm7/sys_time_hw.h
+++ b/sw/airborne/arm7/sys_time_hw.h
@@ -29,7 +29,7 @@
 
 #ifndef SYS_TIME_HW_H
 #define SYS_TIME_HW_H
-
+#include "sys_time.h"
 #include "std.h"
 #include "LPC21xx.h"
 #include BOARD_CONFIG
@@ -118,25 +118,20 @@ static inline void sys_time_init( void ) {
 
 }
 
-#define SYS_TICS_OF_SEC(s)   (uint32_t)(s * PCLK / T0_PCLK_DIV + 0.5)
-#define SYS_TICS_OF_USEC(us) SYS_TICS_OF_SEC((us) * 1e-6)
-#define SYS_TICS_OF_NSEC(ns) SYS_TICS_OF_SEC((ns) * 1e-9)
+#define SYS_TICS_OF_SEC(s)       (uint32_t)(s * PCLK / T0_PCLK_DIV + 0.5)
 #define SIGNED_SYS_TICS_OF_SEC(s) (int32_t)(s * PCLK / T0_PCLK_DIV + 0.5)
-#define SIGNED_SYS_TICS_OF_USEC(us) SIGNED_SYS_TICS_OF_SEC((us) * 1e-6)
 
-#define SEC_OF_SYS_TICS(st) (st / PCLK * T0_PCLK_DIV)
+
+#define SEC_OF_SYS_TICS(st)  (st / PCLK * T0_PCLK_DIV)
 #define MSEC_OF_SYS_TICS(st) (st / (PCLK/1000) * T0_PCLK_DIV)
 #define USEC_OF_SYS_TICS(st) (st / (PCLK/1000000) * T0_PCLK_DIV)
 
 #define GET_CUR_TIME_FLOAT() ((float)cpu_time_sec + SEC_OF_SYS_TICS((float)cpu_time_ticks))
 
-#define FIFTY_MS          SYS_TICS_OF_SEC( 50e-3 )
-#define AVR_PERIOD_MS     SYS_TICS_OF_SEC( 16.666e-3 )
 #ifndef PERIODIC_TASK_PERIOD
 #define PERIODIC_TASK_PERIOD AVR_PERIOD_MS
 #endif
 
-#define TIME_TICKS_PER_SEC SYS_TICS_OF_SEC(1)
 
 #define InitSysTimePeriodic() last_periodic_event = T0TC;
 
diff --git a/sw/airborne/stm32/sys_time_hw.h b/sw/airborne/stm32/sys_time_hw.h
index cd375c1184..33b600d45f 100644
--- a/sw/airborne/stm32/sys_time_hw.h
+++ b/sw/airborne/stm32/sys_time_hw.h
@@ -30,6 +30,8 @@
 #ifndef SYS_TIME_HW_H
 #define SYS_TIME_HW_H
 
+#include "sys_time.h"
+
 #include <stm32/gpio.h>
 #include <stm32/rcc.h>
 #include "std.h"
@@ -45,8 +47,8 @@ extern void sys_tick_irq_handler(void);
 extern volatile bool_t sys_time_period_elapsed;
 extern uint32_t cpu_time_ticks;
 
-#define SYS_TICS_OF_SEC(s)   (uint32_t)((s) * AHB_CLK + 0.5)
-#define TIME_TICKS_PER_SEC SYS_TICS_OF_SEC(1.)
+#define SYS_TICS_OF_SEC(s)        (uint32_t)((s) * AHB_CLK + 0.5)
+#define SIGNED_SYS_TICS_OF_SEC(s)  (int32_t)((s) * AHB_CLK + 0.5)
 
 static inline bool_t sys_time_periodic( void ) {
   if (sys_time_period_elapsed) {
diff --git a/sw/airborne/sys_time.h b/sw/airborne/sys_time.h
index 9e61935da0..8e0501acd9 100644
--- a/sw/airborne/sys_time.h
+++ b/sw/airborne/sys_time.h
@@ -35,8 +35,19 @@
 
 extern uint16_t cpu_time_sec;
 
+#define SYS_TICS_OF_USEC(us) SYS_TICS_OF_SEC((us) * 1e-6)
+#define SYS_TICS_OF_NSEC(ns) SYS_TICS_OF_SEC((ns) * 1e-9)
+#define SIGNED_SYS_TICS_OF_USEC(us) SIGNED_SYS_TICS_OF_SEC((us) * 1e-6)
+#define SIGNED_SYS_TICS_OF_NSEC(us) SIGNED_SYS_TICS_OF_SEC((us) * 1e-9)
+
+#define TIME_TICKS_PER_SEC SYS_TICS_OF_SEC( 1.)
+#define FIFTY_MS           SYS_TICS_OF_SEC( 50e-3 )
+#define AVR_PERIOD_MS      SYS_TICS_OF_SEC( 16.666e-3 )
+
 #ifndef READYBOARD_SYS_TIME
 #include "sys_time_hw.h"
 #endif
 
+
+
 #endif /* SYS_TIME_H */