@staticmethod
def _valid_packet(raw_packet):
    """Validate incoming packet."""
    if raw_packet[0:1] != b'\xcc':
        return False
    if len(raw_packet) != 19:
        return False
    checksum = 0
    for i in range(1, 17):
        checksum += raw_packet[i]
    if checksum != raw_packet[18]:
        return False
    return True
