Get representation name of a pnio frame ID

    :param x: a key of the PNIO_FRAME_IDS dictionary
    :returns: str

def i2s_frameid(x):
    """ Get representation name of a pnio frame ID

    :param x: a key of the PNIO_FRAME_IDS dictionary
    :returns: str
    """
    try:
        return PNIO_FRAME_IDS[x]
    except KeyError:
        pass
    if 0x0100 <= x < 0x1000:
        return "RT_CLASS_3 (%4x)" % x
    if 0x8000 <= x < 0xC000:
        return "RT_CLASS_1 (%4x)" % x
    if 0xC000 <= x < 0xFC00:
        return "RT_CLASS_UDP (%4x)" % x
    if 0xFF80 <= x < 0xFF90:
        return "FragmentationFrameID (%4x)" % x
    return x