var scrolling = null;

    function scroll_up() {
        var d = document.getElementById('scroller');

        d.scrollTop = d.scrollTop - 5;

        scrolling = window.setTimeout(function() {
            scroll_up();
        }, 25);

    }

    function scroll_down() {
        var d = document.getElementById('scroller');

        d.scrollTop = d.scrollTop + 5;

        scrolling = window.setTimeout(function() {
            scroll_down();
        }, 25);
    }

    function stop_scroll() {
        window.clearTimeout(scrolling);
    }