Error when reopen USB connection without physical unplugging USB connection

Question

Using Labview 8.5 to communicate with an USB device based on AT91SAM7S64 controller.
I has written a labview application that talks to several units and it works good as long as i dont close the USB connection
I wants the application to start talking to all USB devices that are already connected, at the moment i must reconnect all USB connection every time I start the Vi.
If a try to reopen a closed USB connection I got an timeout error when I read data from the device
to illustrate the problem I made a dummy test program. (Added as Attachment as jpg and vi)
Senario 1:
If i plug the USB connector into the computer and start the vi the first sequence works fine.
The second sequence fails.
Senario 2:
If i plug the USB connector into the computer and start the vi the first sequence works fine.
If i unplug and plug the USB connector between teh two sequences both works fine
Senario 3
If I remove the VISA close from the first sequence.
If i plug the USB connector into the computer and start the vi the first sequence works fine.
both sequences works fine without needing to unplug the USB connector.
Questions?
Does the VISA close command send a message to the USB device? can this be the reason for the need to replug the connection?
Does it exist a method to reopen a USB connection that has been closed?
All help is good help :-)
Attachments:
USB_error_example.jpg ‏101 KB
USB_error_Example.vi ‏30 KB

Answer 1

Hi Again,
I have tried to recreate the issue when using multiple runs of the same program but this time I have been unable to.  Mine does manage to find the device again.
I have had a word with a few people and they have proposed a solution that would involve writing the references to the registry or a configuration file.  They suggest:
First Run: The program will look to the registery/file to try and find the references.  It wont find any so it will open the VISA references and write them to the registry. This should not close the references at the end of execution.
Run n : The program will look to the registry/file and find the references and use these for VISA operations.
First Run after Reboot: The program will look to the registry/file and find the references but will find that they are invalid so it will open new references and write these to registry for subsequent runs.
Functions for writing to the registry are under connectivity>>windows registry access VIs and have all the usual LabVIEW help files associated with them.
I hope this helps! let me know how it goes.
Message Edited by James McN on 08-07-2008 02:10 PM
James Mc
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CLA and cRIO Fanatic
wiresmithtech.com/blog