function updateOrientation() {
    var newWidth = 0;

    switch(window.orientation) {
        case 0:
            newWidth = 320;
        break;

        case -90:
            newWidth = 480;
        break;

        case 90:
            newWidth = 480;
        break;

        case 180:
            newWidth = 320;
        break;

    }
    
    document.getElementById("viewport").setAttribute('content', 'width = '+newWidth);
}