lock access to serial port

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  • kkadrese@gmail.com
    #1

    lock access to serial port

    hello group,

    how to get ttyS0 serial port for exclusive access? I have a python
    script that uses this device with AT commands. I need that two
    instances can call simultaneosuly this python script but only one of
    them gets the device. I tried fcntl.flock, it was just ignored, put
    writtable file LCK..ttyS0 in /var/lock, tried ioctl (but I may not
    know what are appropriate arguments), googled half a day for various
    phrases, error messages etc....without success.

    please help,

    Andra
    Tags: None
    • taco
      #2
      Re: lock access to serial port

      kkadrese@gmail. com wrote:
      hello group,
      >
      how to get ttyS0 serial port for exclusive access? I have a python
      script that uses this device with AT commands. I need that two
      instances can call simultaneosuly this python script but only one of
      them gets the device. I tried fcntl.flock, it was just ignored, put
      writtable file LCK..ttyS0 in /var/lock, tried ioctl (but I may not
      know what are appropriate arguments), googled half a day for various
      phrases, error messages etc....without success.
      >
      please help,
      >
      Andra
      not sure if I understand you well, but how about a server application which
      accepts 2 clients which can send messages which are output on the serial
      device? The serial device access protected with a mutex while receiving
      messages done in 2 threads or something.
      taco

        Comment

        • kkadrese@gmail.com
          #3
          Re: lock access to serial port

          not the goal setup but the way I tried it out - a webpage to send an
          sms to mobile phone. This is an php what calls a python script. A
          python script opens serial device, checks for gsm network, sends a
          message - on all the way I try to make sure that appropriate answers
          are received from the gsm device so that I know that all is going well
          (and if not - cancel it with error message).

          Testing it with sending an sms from two open webpages, I normally got
          that one message was sent and for the other I received "try once more,
          happened that and that". But I got also an inadmissible situation -
          the received sms contained also unwanted text. As far as I can realize
          how to deal with it is not allowing writing to the device for two
          processes simultaneously.


          Andra


          On 19 Marts, 11:00, taco <trala...@joepi e.nlwrote:
          kkadr...@gmail. com wrote:
          hello group,
          >
          how to get ttyS0 serial port for exclusive access? I have a python
          script that uses this device with AT commands. I need that two
          instances can call simultaneosuly this python script but only one of
          them gets the device. I tried fcntl.flock, it was just ignored, put
          writtable file LCK..ttyS0 in /var/lock, tried ioctl (but I may not
          know what are appropriate arguments), googled half a day for various
          phrases, error messages etc....without success.
          >
          please help,
          >
          Andra
          >
          not sure if I understand you well, but how about a server application which
          accepts 2 clients which can send messages which are output on the serial
          device? The serial device access protected with a mutex while receiving
          messages done in 2 threads or something.
          taco

            Comment

            • Grant Edwards
              #4
              Re: lock access to serial port

              On 2008-03-18, kkadrese@gmail. com <kkadrese@gmail .comwrote:
              how to get ttyS0 serial port for exclusive access? I have a python
              script that uses this device with AT commands. I need that two
              instances can call simultaneosuly this python script but only one of
              them gets the device. I tried fcntl.flock, it was just ignored, put
              writtable file LCK..ttyS0 in /var/lock,
              Using a lock file is the traditional method of providing
              mutually exclusive access to a serial port.
              tried ioctl (but I may not know what are appropriate
              arguments), googled half a day for various phrases, error
              messages etc....without success.
              It's unclear what "without success" means. Lockfiles have been
              used for decades, and they work fine as long as all of the
              applications follow the rules.

              --
              Grant

                Comment

                • kkadrese@gmail.com
                  #5
                  Re: lock access to serial port

                  hmm, now it seems I get to the locking
                  try:
                  ser = serial.Serial(d ev, 19200, rtscts=1, timeout=1)
                  if ser.isOpen():
                  try:
                  fcntl.lockf(ser ,fcntl.LOCK_EX)
                  but get into some weirdness - trying to lock does not time out! The
                  script stops at this line and waits ?for ever? (it waits for 15
                  minutes at least, that I have tried).

                  Andra

                  not the goal setup but the way I tried it out - a webpage to send an
                  sms to mobile phone. This is an php what calls a python script. A
                  python script opens serial device, checks for gsm network, sends a
                  message - on all the way I try to make sure that appropriate answers
                  are received from the gsm device so that I know that all is going well
                  (and if not - cancel it with error message).
                  >
                  Testing it with sending an sms from two open webpages, I normally got
                  that one message was sent and for the other I received "try once more,
                  happened that and that". But I got also an inadmissible situation -
                  the received sms contained also unwanted text. As far as I can realize
                  how to deal with it is not allowing writing to the device for two
                  processes simultaneously.
                  >
                  Andra
                  >
                  On 19 Marts, 11:00, taco <trala...@joepi e.nlwrote:
                  >
                  kkadr...@gmail. com wrote:
                  hello group,
                  >
                  how to get ttyS0 serial port for exclusive access? I have a python
                  script that uses this device with AT commands. I need that two
                  instances can call simultaneosuly this python script but only one of
                  them gets the device. I tried fcntl.flock, it was just ignored, put
                  writtable file LCK..ttyS0 in /var/lock, tried ioctl (but I may not
                  know what are appropriate arguments), googled half a day for various
                  phrases, error messages etc....without success.
                  >
                  please help,
                  >
                  Andra
                  >
                  not sure if I understand you well, but how about a server application which
                  accepts 2 clients which can send messages which are output on the serial
                  device? The serial device access protected with a mutex while receiving
                  messages done in 2 threads or something.
                  taco

                    Comment

                    • Andra
                      #6
                      Re: lock access to serial port

                      I tried ready-made commands for file locking, and turned to that LCK
                      file just in case some permissions are wrong and that's the reason the
                      commands fail.

                      On 19 Marts, 15:43, Grant Edwards <gra...@visi.co mwrote:
                      On 2008-03-18, kkadr...@gmail. com <kkadr...@gmail .comwrote:
                      >
                      how to get ttyS0 serial port for exclusive access? I have a python
                      script that uses this device with AT commands. I need that two
                      instances can call simultaneosuly this python script but only one of
                      them gets the device. I tried fcntl.flock, it was just ignored, put
                      writtable file LCK..ttyS0 in /var/lock,
                      >
                      Using a lock file is the traditional method of providing
                      mutually exclusive access to a serial port.
                      >
                      tried ioctl (but I may not know what are appropriate
                      arguments), googled half a day for various phrases, error
                      messages etc....without success.
                      >
                      It's unclear what "without success" means.  Lockfiles have been
                      used for decades, and they work fine as long as all of the
                      applications follow the rules.
                      >
                      --
                      Grant

                        Comment

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