public function start($iMaxDuration, $iHeartbeat)
    {
        $fNow        = microtime(true);
        $this->aData = [
            'ts_limit'        => $fNow + $iMaxDuration,
            'lap_duration'    => $iHeartbeat,
            'lap_start'       => $fNow,
            'lap_end'         => $fNow + $iHeartbeat,
            'lap_nb_events'   => 0,
            'total_nb_events' => 0
        ];
        return $this;
    }