Chat : Retenir le pseudo

<div id="corps">
    
   <div class="chat"> <form action="minichat_post.php" method="post">
        <p>
		<?php
		if(isset($_SESSION['pseudo'])){
			echo "<b>".$_SESSION['pseudo']."</b><br />";
		}
		else{
		?>
        <label for="pseudo">Pseudo</label> : <input type="text" name="pseudo" id="pseudo" /><br />
		<?php
		}
		?>
        <label for="message">Message</label> :  <input type="text" name="message" id="message" /><br />
        <input type="submit" value="Envoyer" />
	<a href="http://bouboul-IV.legtux.org/minichat.php"><input type=button value="Actualiser"></a>
	</p>

    </form>
</div>

<?php

try{
	$bdd = new PDO('mysql:host=legtux.org;dbname=****', '***', '***');
}
catch(Exception $e){
        die('Erreur : '.$e->getMessage());
}

$reponse = $bdd->query('SELECT pseudo, message, time FROM minichat ORDER BY ID DESC LIMIT 0, 12');


while ($donnees = $reponse->fetch()){
	echo '<p><b>'.htmlspecialchars($donnees['pseudo']).'</b>'.'<b> le '.date('d:m:y  H:i',$donnees['time']) .' </b> :<br /> ' . htmlspecialchars($donnees['message']) . '</p>';
}

$reponse->closeCursor();

?>
</div>

session_start();
if(!isset($_SESSION['pseudo'])){
     $_SESSION['pseudo'] = $_POST['pseudo'];
}