code: func (c *Conn) Close() error {
  	select {
  	case <-c.chDone:
  		// Return if it's already closed.
  		return nil
  	default:
  		c.hci.Send(&cmd.Disconnect{
  			ConnectionHandle: c.param.ConnectionHandle(),
  			Reason:           0x13,
  		}, nil)
  		return nil
  	}
  }
docs: // Close disconnects the connection by sending hci disconnect command to the device.