'Return any data available in the SB ... SE queue.
Return \'\' if no SB ... SE available. Should only be called
after seeing a SB or SE command. When a new SB command is
found, old unread SB data will be discarded. Don\'t block.'

def read_sb_data(self):

    buf = self.sbdataq
    self.sbdataq = ''
    return buf
