diff --git a/sw/airborne/arch/lpc21/subsystems/radio_control/ppm_arch.h b/sw/airborne/arch/lpc21/subsystems/radio_control/ppm_arch.h
index d28ab06338..4374897e5e 100644
--- a/sw/airborne/arch/lpc21/subsystems/radio_control/ppm_arch.h
+++ b/sw/airborne/arch/lpc21/subsystems/radio_control/ppm_arch.h
@@ -35,7 +35,7 @@
  *
  */
 #define RC_PPM_TICKS_OF_USEC(_v)        cpu_ticks_of_usec((_v))
-#define RC_PPM_SIGNED_TICKS_OF_USEC(_v) (int32_t)((_v) * sys_time.cpu_ticks_per_sec * 1e-6)
+#define RC_PPM_SIGNED_TICKS_OF_USEC(_v) ((_v) * sys_time.cpu_ticks_per_sec * 1e-6)
 #define USEC_OF_RC_PPM_TICKS(_v)        usec_of_cpu_ticks((_v))
 
 #define PPM_NB_CHANNEL RADIO_CONTROL_NB_CHANNEL
diff --git a/sw/airborne/arch/stm32/mcu_periph/sys_time_arch.c b/sw/airborne/arch/stm32/mcu_periph/sys_time_arch.c
index baf3cde12b..b550da16e4 100644
--- a/sw/airborne/arch/stm32/mcu_periph/sys_time_arch.c
+++ b/sw/airborne/arch/stm32/mcu_periph/sys_time_arch.c
@@ -37,12 +37,11 @@
 
 /** Initialize SysTick.
  * Generate SysTick interrupt every sys_time.resolution_cpu_ticks
- * The timer interrupt is activated on the transition from 1 to 0,
- * therefore it activates every n+1 clock ticks.
  */
 void sys_time_arch_init( void ) {
-  /* 72MHz / 8 => 9000000 counts per second */
-  sys_time.cpu_ticks_per_sec = AHB_CLK / 8;
+  /* run cortex systick timer with 72MHz */
+  systick_set_clocksource(STK_CTRL_CLKSOURCE_AHB);
+  sys_time.cpu_ticks_per_sec = AHB_CLK;
 
   /* cpu ticks per desired sys_time timer step */
   sys_time.resolution_cpu_ticks = (uint32_t)(sys_time.resolution_sec * sys_time.cpu_ticks_per_sec + 0.5);
@@ -51,10 +50,9 @@ void sys_time_arch_init( void ) {
   sys_time.resolution_sec = (float)sys_time.resolution_cpu_ticks / sys_time.cpu_ticks_per_sec;
   sys_time.ticks_per_sec = (uint32_t)(sys_time.cpu_ticks_per_sec / sys_time.resolution_cpu_ticks + 0.5);
 
-  /* set clock for cortex systick to AHB_CLK / 8 */
-  systick_set_clocksource(STK_CTRL_CLKSOURCE_AHB_DIV8);
-
-  /* 8999 would be one interrupt every 1ms */
+  /* The timer interrupt is activated on the transition from 1 to 0,
+   * therefore it activates every n+1 clock ticks.
+   */
   systick_set_reload(sys_time.resolution_cpu_ticks-1);
 
   systick_interrupt_enable();
diff --git a/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.c b/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.c
index ad69c577c2..566ae2c4f0 100644
--- a/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.c
+++ b/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.c
@@ -97,8 +97,8 @@ void ppm_arch_init ( void ) {
   timer_set_mode(PPM_TIMER, TIM_CR1_CKD_CK_INT,
 		 TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP);
   timer_set_period(PPM_TIMER, 0xFFFF);
-  /* run ppm timer at cpu freq / 8 */
-  timer_set_prescaler(PPM_TIMER, 7);
+  /* run ppm timer at cpu freq / 9 = 8MHz */
+  timer_set_prescaler(PPM_TIMER, 8);
 
  /* TIM configuration: Input Capture mode ---------------------
      The Rising edge is used as active edge,
diff --git a/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.h b/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.h
index b73b18f1b8..66c7238e30 100644
--- a/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.h
+++ b/sw/airborne/arch/stm32/subsystems/radio_control/ppm_arch.h
@@ -33,13 +33,11 @@
 #include "mcu_periph/sys_time.h"
 
 /**
- * While the ppm counter is currently running at the same speed as
- * the systick counter, there is no reason for this to be true.
- * Let's add a pair of macros to make it possible for them to be different.
+ * The ppm counter is running at cpu freq / 9
  */
-#define RC_PPM_TICKS_OF_USEC(_v)        cpu_ticks_of_usec((_v))
-#define RC_PPM_SIGNED_TICKS_OF_USEC(_v) (int32_t)((_v) * sys_time.cpu_ticks_per_sec * 1e-6)
-#define USEC_OF_RC_PPM_TICKS(_v)        usec_of_cpu_ticks((_v))
+#define RC_PPM_TICKS_OF_USEC(_v)        ((_v) * (AHB_CLK / 9000000))
+#define RC_PPM_SIGNED_TICKS_OF_USEC(_v) ((_v) * (AHB_CLK / 9000000))
+#define USEC_OF_RC_PPM_TICKS(_v)        ((_v) / (AHB_CLK / 9000000))
 
 #define PPM_NB_CHANNEL RADIO_CONTROL_NB_CHANNEL