The IEEE 1588 Standard

By Peter Plazotta, TSEP

Synchronizing time between multiple computers in the network has always been a challenge. What is, in the first step, a trivial requirement to equip two or more computers with the identical time is, on closer inspection, a very complex problem. The problem can be defined as follows: 

Distribution of the time of a very precise time source (atomic clock, GPS) on one or more computers in the network. Only the existing network infrastructure is available to distribute the time. 

To solve this problem, the NTP protocol was developed by David L. Mills at the University of Delaware in 1985 and published as RFC 958. With this protocol, it was now possible to assign several computers to the time of a time server. The accuracy is reached in the microsecond range (1x10-6 sec.) And was sufficient at that time. 

As early as 1990, the T & M sector recognized the need to have significantly more precise systems. At this time, GPS systems were also available that could provide a much better accuracy, but this alternative was not attractively priced. In addition, the requirements for improved accuracy with the then existing infrastructure (should) needed to be achieved. For example, at the beginning of the nineties, a working group around John C. Eidson was founded at Hewlett-Packard to develop a concept for the improvement of the NTP standard. The results published in 2000 by John C. Eidson were so interesting for the T & M companies that they wanted to set up their own IEEE standard for this new type of time synchronization. In 2002, the IEEE 1588-2002 was completed and released. With the help of this standard, accuracies in the sub-microsecond range became possible. 

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IVI Web Forum Question and Answer:
64-bit C Visa Clarification

Answered by Ted Wang, National Instruments
for the IVI Web Forum

Note:  Offering an IVI driver is a requirement for all LXI-conformant instruments, something you will find in the LXI Device Specification 2016, Section 6.1. The IVI Web Forum is hosted by the IVI Foundation.It was created to answer the more practical questions that arise when using the IVI Drivers to program test systems. To see a list of the IVI Drivers, click here. To view this question/answer in the Forum, click here.

Question:

If I want to use 64-bit C-Visa do I link to the Visa64.dll or the Visa32.dll? Both are in the system32 dir on a 64-bit O/S. They are both provided by IVI.

What's the difference between these 2 Dll's? Using dependency walker I see they both have the standard VISA API exported but the Visa64.dll depends on other Dll's like: VisaConfigMgr.dll and VisaUtilites.dll; whereas, the Visa32.dll doesn't depend on any other Dlls.

Answer:

You can link to either. The visa32.dll on 64-bit's system32 directory contains entry points that are simply forwarders to the respective visa64.dll entry points. It was created so that users may use the same library name for both 32-bit and 64-bit applications. Here's a snippet of the module definition file:

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Thanks to all our readers.
Bob Helsel, Editor
www.lxistandard.org

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