diff --git a/tests/atmega2560/ordonanceur/ordonanceur.c b/tests/atmega2560/ordonanceur/ordonanceur.c
index c102e98..c668079 100644
--- a/tests/atmega2560/ordonanceur/ordonanceur.c
+++ b/tests/atmega2560/ordonanceur/ordonanceur.c
@@ -84,10 +84,49 @@ asm volatile ( \
 "pop	r0				\n\t" \
 );
 
+/** Configure les ports */
+void init_ports(){
+	//TODO DDRXs
+}
+
+/** ----- Liaison serie ----- */
+void init_serial(int speed){
+	UBRR0 = CPU_FREQ/(((unsigned long int)speed)<<4)-1; //Set baud rate
+	UCSR0B = (1<<TXEN0 | 1<<RXEN0); //Enable transmitter & receiver
+	UCSR0C = (1<<UCSZ01 | 1<<UCSZ00); //Set 8 bits character and 1 stop bit
+	UCSR0A &= ~(1 << U2X0); //Set off UART baud doubler
+}
+void send_serial(unsigned char c){
+	loop_until_bit_is_set(UCSR0A, UDRE0);
+	UDR0 = c;
+}
+unsigned char get_serial(void){
+	loop_until_bit_is_set(UCSR0A, RXC0);
+	return UDR0;
+}
+
+/** ----- Taches ----- */
+void task_print_a(void){
+	while(1){
+		send_serial('a');
+		_delay_ms(1000);
+	}
+}
+void task_print_b(void){
+	while(1){
+		send_serial('b');
+		_delay_ms(700);
+	}
+}
+
+/** ----- Ordonnancement ----- */
 struct task{
 	uint16_t sp_vise;
-	uint8_t state;
 };
+uint8_t cpt = 0;
+uint8_t premier_lancement = 0;
+struct task print_a = {0x0300};
+struct task print_b = {0x0500};
 
 /** Démarre le timer pour l'ordonnancement */
 void init_timer(){
@@ -97,32 +136,43 @@ void init_timer(){
 	OCR1A = NB_TICK;
 	TIMSK1 |= _BV(OCIE1A);
 }
-
-/** Configure les ports */
-void init_ports(){
-	//TODO DDRXs
-}
-
-/** Alumme la LED 13 pour témoigné du bon fonctionnement de la carte */
-void temoin_allumage(){
-	DDRA = 0x01;
-	PORTA = 0x01;
-	_delay_ms(500);
-	PORTA = 0x00;
-}
-
-/** Reception de l'interruption généré par le timer (changement de contexte) */
+/** Changement de contexte */
 ISR(TIMER1_COMPA_vect){
-	// TODO
+	if(premier_lancement == 0){
+		premier_lancement++;
+		sei();
+		SP = print_a.sp_vise;
+		task_print_a();
+	}else if(premier_lancement == 1){
+		SAVE_CONTEXT();
+		print_a.sp_vise = SP;
+		premier_lancement++;
+		sei();
+		SP = print_b.sp_vise;
+		task_print_b();
+	}else{
+		if(cpt==0){
+			SAVE_CONTEXT();
+			print_b.sp_vise = SP;
+			SP = print_a.sp_vise;
+			RESTORE_CONTEXT();
+			cpt++;
+		}else if(cpt==1){
+			SAVE_CONTEXT();
+			print_a.sp_vise = SP;
+			SP = print_b.sp_vise;
+			RESTORE_CONTEXT();
+			cpt = 0;
+		}
+	}
 	sei();
 }
 
 int main(void){
-	temoin_allumage();
-
 	// Initialisation
 	init_timer();
-	init_port();
+	init_ports();
+	init_serial(9600);
 	sei();
 
 	while(1){}
--
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