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[ASCOM] Re: HOWTO Use a hub to make multiple simultaneous connections to an ASCOM driver

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  • jcmoore_uk
    Tim, Sorry for the delayed reply - I ve had difficulty getting into this group for the last two days. Just wanted to say many thanks for the explanation re
    Message 1 of 8 , Feb 2, 2013
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      Tim,

      Sorry for the delayed reply - I've had difficulty getting into this group for the last two days. Just wanted to say many thanks for the explanation re different hubs. I've switched to the generic hub now and that seems to work fine too.

      Incidentally, I remember that when the recently introduced Gemini .NET telescope driver came out it was touted as providing an inherent hub capability, and worked well for me. I don't use Gemini any more, but am curious to know if this too could suffer from similar problems when two or more clients are connected?

      Regards
      John Moore
    • Tim Long
      Well, you d have to ask the Gemini driver developers for a definitive answer, but I suspect that it is an inherently unsolvable problem. One can t know in
      Message 2 of 8 , Feb 4, 2013
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        Well, you'd have to ask the Gemini driver developers for a definitive
        answer, but I suspect that it is an inherently unsolvable problem. One
        can't know in advance what any connected program will try to do, so
        there is no way you can know how to plan for it.

        I don't want to make this seem like a worse problem than it is. The fact
        is, a lot of people use hubs all the time and they work just fine.
        That's because most people use them as a convenience and because most
        control programs are fairly 'well behaved' - when they are idle, they
        don't send commands to their ASCOM drivers. So as long as the programs
        are used interactively, one at a time, then things usually work out OK.
        The fact that it works is a happy accident rather than something that
        can be deliberately planned for. To exaggerate the point slightly, If
        you were to start a scripted operation in one of your programs, let's
        say an all-sky mapping run or something, then you switch to the other
        program and start controlling the telescope from there, then it is easy
        to imagine how you could really mess with the script that's running in
        the background, and neither the hub nor the driver could do anything to
        prevent it.

        Best regards,
        Tim Long


        -----Original Message-----
        From: ASCOM-Talk@yahoogroups.com [mailto:ASCOM-Talk@yahoogroups.com] On
        Behalf Of jcmoore_uk
        Sent: 03 February 2013 00:12
        To: ASCOM-Talk@yahoogroups.com
        Subject: [ASCOM] Re: HOWTO Use a hub to make multiple simultaneous
        connections to an ASCOM driver

        Tim,

        Sorry for the delayed reply - I've had difficulty getting into this
        group for the last two days. Just wanted to say many thanks for the
        explanation re different hubs. I've switched to the generic hub now and
        that seems to work fine too.

        Incidentally, I remember that when the recently introduced Gemini .NET
        telescope driver came out it was touted as providing an inherent hub
        capability, and worked well for me. I don't use Gemini any more, but am
        curious to know if this too could suffer from similar problems when two
        or more clients are connected?

        Regards
        John Moore




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      • paulkccd
        Gemini.NET driver works as a hub using local server template. It works just fine with as many clients as you d like to connect to it. It even supports
        Message 3 of 8 , Feb 5, 2013
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          Gemini.NET driver works as a hub using local server template. It works just fine with as many clients as you'd like to connect to it. It even supports non-ASCOM clients connected over a virtual serial port. Most commands are performed atomically, that is the driver will ensure that a command is completed before executing the next command.

          But, as Tim points out, it is an unsolvable problem to prevent conflicting commands from being issued by multiple clients given the current state of the ASCOM API. Fixing this involve a more complex transactional semantics that is not part of ASCOM definition.

          So far, this has not been an issue for our users, since most software use the driver for polling (a read-only operation) in their idle state.

          Regards,

          -Paul


          --- In ASCOM-Talk@yahoogroups.com, "Tim Long" wrote:
          >
          > Well, you'd have to ask the Gemini driver developers for a definitive
          > answer, but I suspect that it is an inherently unsolvable problem. One
          > can't know in advance what any connected program will try to do, so
          > there is no way you can know how to plan for it.
          >
          > I don't want to make this seem like a worse problem than it is. The fact
          > is, a lot of people use hubs all the time and they work just fine.
          > That's because most people use them as a convenience and because most
          > control programs are fairly 'well behaved' - when they are idle, they
          > don't send commands to their ASCOM drivers. So as long as the programs
          > are used interactively, one at a time, then things usually work out OK.
          > The fact that it works is a happy accident rather than something that
          > can be deliberately planned for. To exaggerate the point slightly, If
          > you were to start a scripted operation in one of your programs, let's
          > say an all-sky mapping run or something, then you switch to the other
          > program and start controlling the telescope from there, then it is easy
          > to imagine how you could really mess with the script that's running in
          > the background, and neither the hub nor the driver could do anything to
          > prevent it.
          >
          > Best regards,
          > Tim Long
          >
          >
          > -----Original Message-----
          > From: ASCOM-Talk@yahoogroups.com [mailto:ASCOM-Talk@yahoogroups.com] On
          > Behalf Of jcmoore_uk
          > Sent: 03 February 2013 00:12
          > To: ASCOM-Talk@yahoogroups.com
          > Subject: [ASCOM] Re: HOWTO Use a hub to make multiple simultaneous
          > connections to an ASCOM driver
          >
          > Tim,
          >
          > Sorry for the delayed reply - I've had difficulty getting into this
          > group for the last two days. Just wanted to say many thanks for the
          > explanation re different hubs. I've switched to the generic hub now and
          > that seems to work fine too.
          >
          > Incidentally, I remember that when the recently introduced Gemini .NET
          > telescope driver came out it was touted as providing an inherent hub
          > capability, and worked well for me. I don't use Gemini any more, but am
          > curious to know if this too could suffer from similar problems when two
          > or more clients are connected?
          >
          > Regards
          > John Moore
          >
          >
          >
          >
          > ------------------------------------
          >
          > For more information see http://ASCOM-Standards.org/.
          >
          > To unsubscribe from this group, send an email FROM THE ACCOUNT YOU USED
          > TO SUBSCRIBE(!) to:
          > ASCOM-Talk-unsubscribe@yahoogroups.com
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
          > --
          > ExchangeDefender Message Security: Click below to verify authenticity
          > http://www.exchangedefender.com/verify.asp?id=r150LVTo024257&from=tim@...
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