6120 stops working on windows when changing kvm

[malmon]

I have a 6120 running on several windows 7 (64 bit) systems and several XP (32 bit) systems.  I have grouped the computers onto KVM switches (4 systems per switch), so I can share the keyboard mouse and video, but each computer has a 6210 which is directly plugged into the computer.  If I am taking a measurement in the daq on any system and let it run it works fine, but when I switch to another system and then come back the daq will error number -50405. 

I am suspect that it is the KVM switch I am using because I have used others in the past and they work with the same setup.

[JustinP]

Hello,

The error you are seeing generaly occurs when the USB device loses communication or gets reset.  This could occur if the the current on the USB hub within the PC drops or spikes due to the KVM switching between systems.  This document discusses the loss of communication. You can try alternate USB ports on the computer and see if that produces more stable behavior. Could you provide the make and model of the KVM switch?

Regards,

Justin

[malmon]

The KVM is a StarTech SV431DPUA (http://us.startech.com/product/SV431DPUA-4-Port-USB-DisplayPort-KVM-Switch-with-Audio).  I have also contacted their support and I am waiting on a reply from them on this matter.

Thank you for the link I am going to try and use a powered usb hub to see if that solves the problem.

[malmon]

Hi,

So I have tried using the same KVM on another set of 4 computers with no errors when switching.  I ran a test on the working computers using MAX to continuously read the the voltage, and just switched the keyboard and mouse and had the video directly plugged in and noticed that there was a lag in the readings during the KVM switching.  Could the pauses during the switching event cause the DAQ to be dropped?

Thanks

[Seth_B.]

Often, system events like adding and removing USB devices, particularly Human Interface Devices (HID) can cause the OS to dedicate more resources to those devices, leaving less or possibly none to service the DAQ USB stream.  This is an unfortunate side effect of USB and a non-deterministic OS like Windows, OSX, or Linux.

If you need to be switching the keyboard and mouse to and from a system repeatedly, you'll either want to choose a sampling rate/samples to read combination that is very tolerant of occasionally not being able to transfer everything immediately or implement some error handling to discard time out or buffer overflow errors.