code: def handle_feedback(self, pkt):
          
          self.logger.debug("handle feedback")
          self.frame = self.decode_frameno(pkt.z & 0o7777) - 1
  
          # erase the frame buffer
          self.server.controller.init_frame(self.frame)
          self.server.controller.set_frame(self.frame)
docs: This part of the protocol is used by IRAF to erase a frame in
          the framebuffers.