diff --git a/sw/airborne/avr/spi_hw.c b/sw/airborne/avr/spi_hw.c
index 76c452da91..430d6bf6a2 100644
--- a/sw/airborne/avr/spi_hw.c
+++ b/sw/airborne/avr/spi_hw.c
@@ -123,24 +123,24 @@ void spi_init( void) {
 /** SPI interrupt: starts a delay */
 SIGNAL(SIG_SPI) {
   /*  if (spi_cur_slave == SPI_SLAVE0) { */
-    /* setup OCR1C to pop in 200 clock cycles */
-    /* this leaves time for the slave (fbw) */
-    /* to process the byte we've sent and to  */
-    /* prepare a new one to be sent           */
-    OCR1C = TCNT1 + 200;
-    /* clear interrupt flag  */
-    SetBit(TIFR, OCF1C);
-    /* enable OC1C interrupt */
-    SetBit(TIMSK, OCIE1C);
-    /*  } else
-    fatal_error_nb++;
-    */
+  /* setup OCR1C to pop in 200 clock cycles */
+  /* this leaves time for the slave (fbw) */
+  /* to process the byte we've sent and to  */
+  /* prepare a new one to be sent           */
+  OCR1C = TCNT1 + (200UL*CLOCK)/16;
+  /* clear interrupt flag  */
+  SetBit(ETIFR, OCF1C);
+  /* enable OC1C interrupt */
+  SetBit(ETIMSK, OCIE1C);
+  /*  } else
+      fatal_error_nb++;
+  */
 }
 
 /** Send a byte */
 SIGNAL(SIG_OUTPUT_COMPARE1C) {
   /* disable OC1C interrupt */
-  ClearBit(TIMSK, OCIE1C);
+  ClearBit(ETIMSK, OCIE1C);
 
   HandleOneSpiByte();
 }
diff --git a/sw/airborne/avr/sys_time_hw.h b/sw/airborne/avr/sys_time_hw.h
index de6aa0819d..f02051743a 100644
--- a/sw/airborne/avr/sys_time_hw.h
+++ b/sw/airborne/avr/sys_time_hw.h
@@ -55,7 +55,14 @@ static inline void sys_time_init( void ) {
 #if defined (__AVR_ATmega8__)
   TCCR2         = _BV(CS20) | _BV(CS21) | _BV(CS22);
 #elif defined (__AVR_ATmega128__)
+#if CLOCK == 16
   TCCR2         = _BV(CS20) | _BV(CS22);
+#elif CLOCK == 8
+  TCCR2         = _BV(CS22);
+  sbi( TIMSK, TOIE2 );
+#else
+#error "Unknwon CLOCK"
+#endif
 #else
 #warning "Unknown arch"
 #endif
@@ -72,20 +79,45 @@ static inline void sys_time_init( void ) {
 
 #define SYS_TICS_OF_USEC(us) (uint16_t)((us)*CLOCK)
 #define SIGNED_SYS_TICS_OF_USEC(us) (int16_t)((us)*CLOCK)
+
+#if CLOCK == 8
+#define LONG_SYS_TICS_OF_USEC(us) (uint16_t)(((uint32_t)(us)*CLOCK)/256ul)
+#else
 #define LONG_SYS_TICS_OF_USEC(us) (uint8_t)(((uint32_t)(us)*CLOCK)/1024ul)
+#endif
 
 /*
  *  Periodic tasks occur when Timer2 overflows.  Check and unset
- * the overflow bit. Occurs at 61.03515625 Hz
+ * the overflow bit. Occurs at 61.03515625 Hz with CLOCK = 16
+ * Occurs at 122Hz with CLOCK = 8
  *
  */
+
+#if CLOCK == 8
+extern volatile uint8_t tmr2_ov_cnt;
+extern volatile bool_t tmr2_overflow;
+#endif
+
+
+#if CLOCK == 8
+static inline bool_t sys_time_periodic( void ) {
+  if( !tmr2_overflow )
+    return FALSE;
+  tmr2_overflow = FALSE;
+
+  return (tmr2_ov_cnt & 0x1);
+}
+
+#else 
+
 static inline bool_t sys_time_periodic( void ) {
   if( !bit_is_set( TIFR, TOV2 ) )
     return FALSE;
   TIFR = _BV(TOV2);
+
   return TRUE;
 }
 
-
+#endif
 
 #endif /* SYS_TIME_HW_H */
diff --git a/sw/airborne/spi.c b/sw/airborne/spi.c
index c1fb88de7a..44ab7913ee 100644
--- a/sw/airborne/spi.c
+++ b/sw/airborne/spi.c
@@ -22,6 +22,7 @@
  *
  */
 
+#include "std.h"
 #include "spi.h"
 
 uint8_t* spi_buffer_input;