Upgrading VXI Systems from VXI-MXI-2 to VXI-8340 Series (MXI-3)

Hardware: VXI/VME/MXI>>MXI Interfaces>>VXI-MXI-2

Problem:
What are the issues involved in upgrading from VXI-MXI-2 to VXI-8340 (based on MXI-3 technology)?

Solution:
The VXI-8340 Series offers two main advantages over VXI-MXI-2. First, VXI-8340 systems can be setup with smaller, lighter, more flexible cables, as opposed to the thick, double cables of VXI-MXI-2. Additionally, the VXI-8345 fiber-optic kit provides a maximum separation of 200 meters between the VXI chassis and controlling computer. However, there are some technical items that need to be considered before upgrading a system from VXI-MXI-2 to VXI-8340 Series:

Boot Order:
The VXI-8340 Series VXI controllers use MXI-3 technology, which is based on PCI-PCI bridge technology. Since PCI-PCI bridges are configured by the BIOS, the VXI Chassis must be powered on before the computer is powered on (just like PXI-MXI-3). This is not the case with VXI-MXI-2. The VXI-8340 Series provides the ability to power-cycle the VXI chassis without power-cycling the controlling computer. This is done by either pressing the "powercycle" button on the VXI-8340 card, or by right-clicking in MAX and selecting "Request Offline".
Drivers:
Upgrading to the VXI-8340 Series interface may require a driver upgrade. Please check the Current NI-VXI Driver Versions page to find the recommended driver for your system.
Throughput:
Although, both the VXI-MXI-2 and VXI-8340 Series interfaces are both high-performance VXI controllers, they do vary in throughput. In addition, throughput is affected by other system variables, such as the OS and processor, as well as the type of transfer. The theoretical maximum throughput for VXI-MXI-2 is quoted at 33 Mbytes/s burst and 14.5 Mbytes/s sustained transfer. The maximum throughput for VXI-8340 Series is quoted at 16 Mbytes/s.

Converting a Single Chassis from VXI-MXI-2 to VXI-8340
Converting a single chassis VXI-MXI-2 system to VXI-8340 Series should be straightforward. The VXI-8340 Series hardware completely supports the VXI specification, so all existing VXI features remain in their same form. This includes configuration of instruments by the VXI Resource Manager (Resman), shared memory, signals, interrupts, triggers, etc. Additionally, existing software, whether based on VXI functions (i.e. VXIin, VXIout) or VISA functions (i.e. viRead, viIn16, viOut16), should work without modifications.

Converting a Multi-Chassis System from VXI-MXI-2 to VXI-8340
With VXI-MXI-2, multi-chassis systems were configured using logical address windows. Each chassis in the system would have a window of logical addresses available in that particular chassis in the system. For example, a two chassis system with VXI-MXI-2 may use logical addresses 0-15 for a first chassis, and logical addresses 16-31 for a second chassis. Therefore, a multi-chassis system using VXI-MXI-2 would have the following typical hierarchy under the "Devices" view in Measurement and Automation Explorer (MAX).

Example of a Two Chassis System in MAX with VXI-MXI-2:

When you have a multi-chassis system with VXI-8340 Series controllers, then each VXI chassis is a distinct, separate VXI system in MAX. For example, if you had two VXI-8340 chassis in a daisy-chained or star configuration, then the first chassis would be listed in MAX as "VXI System 0" and the second chassis would be listed in MAX as "VXI System 1."

Example of a Two Chassis System in MAX with VXI-MXI-3:

Since these are distinct and separate VXI systems, it is possible to have one instrument in each chassis at the same logical address. The NI-VXI API does not take into account multiple VXI systems. As a result, to talk to a given instrument in either chassis, you would now need to use VISA sessions to "VXIx::y::INSTR" where "x" is the VXI system number, and "y" is the logical address of the device in the chassis for that system.

If the existing software for your system is based on VISA, and is written in such a way that you can simply change an instrument descriptor (such as "VXI0::15::INSTR" to "VXI1::15::INSTR"), then completely transitioning a system to VXI-MXI-2 to VXI-8340 should not be difficult. You can simply change the instrument descriptors in their VISA code. Unfortunately, if you used the NI-VXI API, or used the VISA API in such a way that instrument addresses are hard-coded, then a complete conversion from VXI-MXI-2 to VXI-8340 would require re-work of the software. As an aside, you can configure in MAX which VXI system number the NI-VXI API will use.

Note: There is another alternative. With a multi-chassis system, you could convert the computer-to-first-chassis VXI-MXI-2 interface to a VXI-8340 Series interface . This allows you to capture one of the advantages of VXI-8340 by increasing the maximum distance between VXI system and controlling computer (up to 200 m). For the chassis-to-chassis connections, you could still use VXI-MXI-2. Since MXI-2 is a VXIbus extender, the multi-chassis configuration remains a single VXI system (VXI System 0) in software. Therefore, existing NI-VXI and/or NI-VISA code would not have to be modified.

Related Links:
VXI Support: Current NI-VXI Driver Versions
VXI-8340 Series User Manual
Products and Services: NI VXI-PCI8015
Products and Services: NI VXI-PCI8340
Products and Services: NI VXI-PCI8345

Attachments:

Report Date: 10/31/2001
Last Updated: 01/27/2006
Document ID: 2EUAQOLS

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