Problema con variabile e funzioni.

[andbaz]

Non mi stampa la variabile fa, perchè?

<?php

    function post() {    
        global $fa;
        $sql = "SELECT COUNT(*) FROM post"; 
        $query = mysql_query($sql);
        $row = mysql_fetch_row($query);     
        if ($row[0] > 0) {
            $sql = "SELECT * FROM post ORDER BY IDP DESC";            
            $query = mysql_query($sql) or die (mysql_error());                                                                        
            while ($row = mysql_fetch_assoc($query)) {                                    
                $text = $row['TESTO'];
                $date = $row['DATA'];
                $time = $row['TS'];
                $com = $row['COM'];
                $piu = $row['PIU'];    

                tempo();
                                
                $post = "
                    <div id='div13'>
                        $text
                        $fa
                    </div>                    
                ";
                
                echo $post;
            }
        }
    }
    
    function tempo() {
        global $time;
        $now = time();
        $ris = $now - $time;
        if ($ris>5 && $ris<10) {
            $fa = '5 secondi fa';
        } else if ($ris>10 && $ris<20) {
            $fa = '10 secondi fa';
        } else {
            $fa = 'lol';
        }
    }
    
?>