let do_command ?(timeout=1.0) ?(no_err=false) ?(retval=true) cmd =
    let cmd_task =
      lwt () = info_f ">>> %S" cmd in
      lwt () = serial#write ~delay ("@"^cmd^"\r\n") in
      if retval then
        lwt u = splitter () in
        return (`OK u)
      else
        return (`OK "")
    in
    let timeout_task =
      lwt () = Lwt_unix.sleep timeout in
      return `Timeout
    in
    lwt result = cmd_task <?> timeout_task in
    cancel timeout_task;
    cancel cmd_task;
    return result
  in
...