TCP comm with multiple instruments

LV 2010, Windows, LVRT
I need to communicate with several (5-50, I don't know) separate identical instruments via TCP.
I have to send requests and receive answers, more or less continuously.
I like state machines for doing this, but this particular model doesn't fit my way of doing things.
The driver that comes with it was built with the attitude that this is the only unit tied to the CPU so you don't have anything better to do than to wait on this one unit.
The responses are ASCII, and they come back terminated with a LF (not CRLF).
I can't change that in the machine. So I cannot use TCP READ (crlf mode).
What the driver does is to issue a command to the box, then a TCP READ (immediate), with a timeout of 100-200 mSec.
Some responses come back in 1-2 mSec, some take 130-150 mSec.
I can't sit there and wait for 150 mSec, I have other stuff to do.
What I have done if it's BINARY or CRLF terminated is to use TCP READ(buffered) with a zero timeout.
If I get a timeout error, the complete message is not there yet, so I go do something else and come back later.
That lets me keep 10 of them busy without waiting on any of them.
Since it is ASCII, I don't know how long the messages will be (can't use BUFFERED mode).
Since it's LF terminated, I cannot use CRLF mode.
I could implement my own buffering scheme, where I retrieve whatever is there with zero timeout, append it to a buffer for this device, search for LF characters and report messages that way.
Anybody got a better idea?
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

I didn't get though how you handle the different connections. Do you have an array of 5-50 TCP references?
Yeah, there's a STATE cluster for each unit, with a CONN ID (and other info) in each one.
Another approach I could think of is to spawn a handler for each of the connections. Create an instance of a reentrant VI for each connection, then you don't care if the TCP read in a specific handler VI is waiting for data. The other (independant) handler VIs can continue to run.
I didn't think of spawning one. I have previously used a MASTER, which maintains N instances of a re-entrant CORE, which does the work.
I didn't do that here because I don't know what N will be. I also don't know which one needs service the soonest, and I'm trying to avoid servicing units that don't need it.
But I'll give it another think. Thanks!
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

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Attachments:
server.vi ‏229 KB
client.vi ‏28 KB

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Attachments:
errror1.JPG ‏26 KB

Hi Pavel,
For the purposes of this post, I'll define
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For the
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simultaneously.
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look at what happens when we setup a system with multiple switch
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If you'd still like to use NI-Switch, you could roll back to DAQmx 8.9.5 or previous, or if you want to stick with 9.0.x, I highly recommend that we daisy chain the triggers as follows:
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Message Edited by Knights Who Say NI on 06-11-2010 05:25 PM
Message Edited by Knights Who Say NI on 06-11-2010 05:30 PM
Message Edited by Knights Who Say NI on 06-11-2010 05:30 PM
Message Edited by Knights Who Say NI on 06-11-2010 05:31 PM
-John Sullivan
Analog Engineer

Can I communicate single PXI chassis with multiple computer using MXI

Can I communicate single PXI chassis with multiple computer using multiple MXI cards
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Jacob K || Applications Engineer || National Instruments
Attachments:
PXIMaster.png ‏20 KB

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