diff --git a/system/clkhandler.c b/system/clkhandler.c
index 3759d2b..21dc18d 100644
--- a/system/clkhandler.c
+++ b/system/clkhandler.c
@@ -4,42 +4,62 @@
 
 #include <xinu.h>
 
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+volatile unsigned int avr_ticks=0;
+
 /*-----------------------------------------------------------------------
  * clkhandler - high level clock interrupt handler
  *-----------------------------------------------------------------------
  */
-void clkhandler()
+
+/* void clkhandler() */
+
+ISR(TIMER0_COMPA_vect)
 {
-	struct timer_csreg *tptr;
 
-	/* Increment 1000ms counter */
+	/* Every ms: What TO DO */
 
-	count1000++;
+	/* every second */
+	/* if avr_ticks == 1000 then 1 second */
 
-	/* After 1 sec, increment clktime */
+	avr_ticks ++;
+	if (avr_ticks > 100) {
+		avr_ticks=0;
 
-	if(count1000 >= 1000) {
-		clktime++;
-		count1000 = 0;
-	}
 
-	/* check if sleep queue is empty */
+	       /* Increment 1000ms counter */
 
-	if(!isempty(sleepq)) {
-		/* sleepq nonempty, decrement the key of */
-		/* topmost process on sleepq		 */
+		count1000++;
 
-		if((--queuetab[firstid(sleepq)].qkey) == 0) {
+		/* After 1 sec, increment clktime */
 
-			wakeup();
+		if(count1000 >= 1000) {
+			clktime++;
+			count1000 = 0;
 		}
-	}
 
-	/* Decrement the preemption counter */
-	/* Reschedule if necessary	    */
+		/* check if sleep queue is empty */
+
+		if(!isempty(sleepq)) {
+			/* sleepq nonempty, decrement the key of */
+			/* topmost process on sleepq             */
 
-	if((--preempt) == 0) {
-		preempt = QUANTUM;
-		resched();
+			if((--queuetab[firstid(sleepq)].qkey) == 0) {
+
+				wakeup();
+			}
+		}
+
+		/* Decrement the preemption counter */
+		/* Reschedule if necessary          */
+
+		if((--preempt) == 0) {
+			preempt = QUANTUM;
+			resched();
+		}
 	}
+
 }
+
diff --git a/system/clkinit.c b/system/clkinit.c
index eadd0ac..8862ad3 100644
--- a/system/clkinit.c
+++ b/system/clkinit.c
@@ -8,9 +8,11 @@
 #include <avr/interrupt.h>
 
 uint32	clktime;		/* Seconds since boot			*/
-uint32  count1000;              /* ms since last clock tick             */
+// RAFA uint32  count1000;              /* ms since last clock tick             */
+unsigned long  count1000;              /* ms since last clock tick             */
 qid16	sleepq;			/* Queue of sleeping processes		*/
-uint32	preempt;		/* Preemption counter			*/
+// RAFA uint32	preempt;		/* Preemption counter			*/
+unsigned long preempt;		/* Preemption counter			*/
 
 /*------------------------------------------------------------------------
  * clkinit  -  Initialize the clock and sleep queue at startup
@@ -30,39 +32,16 @@ void clkinit(void)
 	clktime = 0;		/* Start counting seconds		*/
         count1000 = 0;
 
-	/* AVR atmega328p timer/clock init: interrupt every 1ms */
 
+	/* 
+         * AVR atmega328p timer/clock init: interrupt every 1ms 
+	 * The AVR TIMER interrupt rutine is in clkhandler.c
+         */
 	TCCR0B |= (1<<CS01) | (1<<CS00);   //clock select is divided by 64.
 	TCCR0A |= (1<<WGM01);              //sets mode to CTC
-	// OCR0A = 0x7C;                      //sets TOP to 124 so the timer will overflow every 1 ms.    
 	OCR0A = 0xF9;                      //sets TOP to 124 so the timer will overflow every 1 ms.    
 	TIMSK0 |= (1<<OCIE0A);              //Output Compare Match A Interrupt Enable
 
 	return;
 }
 
-
-
-
-unsigned int avr_ticks=0;
-
-ISR(TIMER0_COMPA_vect)
-{
-	cli();
-
-	/* Every ms: What TO DO */
-	// clkhandler();
-
-
-	avr_ticks ++;
-	if (avr_ticks > 100) {
-		avr_ticks=0;
-		resched();
-	}
-
-	/* every second */
-	/* if avr_ticks == 1000 then 1 second */
-
-	sei();
-}
-
diff --git a/system/intr.c b/system/intr.c
index fa1d611..f939d10 100644
--- a/system/intr.c
+++ b/system/intr.c
@@ -1,45 +1,34 @@
-/* Xinu for AVR
- *
- * Original license applies
- * Modifications for STM32 by Robin Krens
- * Please see LICENSE and AUTHORS 
- * 
- * $LOG$
- * 2019/11/11 - ROBIN KRENS
- * Initial version 
- * 
- * $DESCRIPTION$
- *
- * */
-
 /* intr.S - enable, disable, restore, halt, pause, (ARM) */
 
+/* avr specific */
+
 #include <xinu.h>
 #include <avr/interrupt.h>
 
-
-/* RAFA: the arguments and returns do not have any meaning. It were there
- * for STM32.
- * 
- * For AVR: remove them some day
+/*
+ *  This code is based on AVR-Xinu by Michael Minor
  */
 
+#include <avr/io.h>
+
 /*------------------------------------------------------------------------
  * disable  -  Disable interrupts and return the previous state
  *------------------------------------------------------------------------
  */
-intmask disable() {
-	cli();
-	return 0;
+intmask disable(void)
+{
+	int x = SREG;
+	asm("cli");	/*and disable interrupts*/
+	return x;
 }
 
 /*------------------------------------------------------------------------
  * restore  -  Restore interrupts to value given by mask argument
-   Cortex M3 hardware handles a lot, rewrite
  *------------------------------------------------------------------------
  */
-inline void restore(intmask c) {
-	sei();
+void restore(uint8 x)
+{
+	SREG = x;	/*restore the status register, possibly reenabling interrupts*/
 }
 
 /*------------------------------------------------------------------------