Computing Requirements in Multiple PXI Chassis System

[JMU_ISAT]

I have acquired a two PXI Chassis system, each with their own embedded controller (PXIe-8108 and PXIe-8130).  I would like to control all instruments (simultaneously) in both chassis from a central location (either a laptop or one of the embedded controllers).  What is the best configuration for this and will using one controller have enough power to drive two fully populated PXIe-1065 chassis?

(I am aware of the different configurations for control (MXI, etc.) and am more concerned with instrument performance, data buffers become full quickly etc., in using one PC controller)

THANKS!

[Andy-K]

Hi JMU_ISAT,

The PXIe-1065 chassis uses a four link configuration where there is an x4 link going to slots 7, one to slot 8, another to slots 9-14.  There are also an x1 link converted to PXI that goes to slots 2-7 and another x1 link converted to PXI that goes to slots 11-13 and 15-18.  Each x4 link gives 1 GB/s of bandwidth and each x1 link converted to PXI will provide 125 MB/s of bandwidth.  These bandwidths are theoretical maximums where overhead and chip design reduces the bandwidth somewhat.  

The PXI-8130 has four x4 links with the four link configuration so it will be able to get the full chassis bandwidth.  The PXIe-8108 has four x1 links which will limit the bandwidth to 250 MB/s for slot 7, slot 8, and slot 9-14.

To synchronize the measurements across both chassis you will need a timing and synchronization module such as the PXIe-6672 in the timing slot of each chassis.  This will allow you to route the clock of one timing module to the other and then use that clock to override the backplane reference clock of each chassis.  Now each module can use the 10 MHz reference clock to synchronize to each other.

In order to control both chassis from one controller, you can run windows on one controller and LabVIEW RealTime on the other controller allowing you to distribute code from the windows controller to the LabVIEW RealTime controller.  The other method would be to run a MXI connection from one chassis to the other to daisy chain the chassis.  Since the most you can get out of a single slot of the PXIe-1065 is an x4 link, this would limit the total bandwidth of the daisy chained chassis to 1 GB/s theoretical maximum.

I hope this information is helpful!

[JMU_ISAT]

Your response is certainly helpful.

The reason the "engineer" who developed this system prior designed it this way (client-server config with external pc accessing PXI cards of the two chasis via making calls to the (2) embedded controllers over ethernet) was that he assumed that since the PXI instruments are "headless" they require more computing power which he wanted to distribute across the two controllers.  Is this really not an issue?  The current setup works, but is a real pain to develop for as the client-server configuration seems overly complex just to get access to the PXI cards.

Thanks for the bandwidth specs.

[Anthony_F]

Hello JMU_ISAT,

The MXI connection is going to have lower latency than ethernet and will be faster than 100Mb ethernet.  Take a look at the Instrument Bus Performance tutorial to compare the different connections.  You can think of MXI as an extension of the PCI bus.

Like Andy mentioned previously, different slots have different bandwidths, and it is possible the engineer was using a low bandwidth slot when testing.  If you think about just the data throughput, the same amount of data has to get to the master controller, you will be limited by the connection method you choose.

[JMU_ISAT]

Maybe I'm not posing this question properly or I simply misunderstand how much "computing" the individual PXI cards are capable of...What I'm really interested in is the demand the individual PXI cards will have on the controller CPU while they are taking measurements, Tx/Rx, etc..I understand part of the limitation will be in the throughput of the data bus/backplane.

Specifically, I will have two fully populated PXIe-1065 chassis.  If there is one embedded controller (PXI-8108) and a MXI card in the other chassis, how will the system perform when several things simultaneously occur i.e. DMM card taking high speed measurements, VSG and VSA cards transmitting/receiving complex waveforms respectively, and visual display and processing of acquired data?

I guess the real question is how taxing are the PXI cards/instruments on the PC controller once they have been initialized/configured/ and start to perform the desired task?

[Anthony_F]

JMU, just to have all the PXI cards running is not CPU intensive, it is just a matter of moving data from the PXI cards into some other memory area like RAM or the harddrive. Problems will occur when you try to process all that data inside the program so it is highly dependent on the program running on each chassis.

I would open up the Windows Task Manager and watch the CPU processing level as well as memory usage (RAM and disk space) on both chassis while running the program.

Based upon your findings it should be easy to tell if the second chassis is doing any processing that the first chassis could be doing.  For example, if the second chassis takes the measurements as-is and forwards them to the ethernet port with no additional processing, you are not gaining anything by having an embedded controller in that chassis (as it is not being used to its full potential).

Please let me know if anything was unclear or if I can explain better.

[KarlJason]

Hi Guys,

I have a question which I think is related to this post.

Is it possible for me to control:

1) PXIe-1073 plus PXIe-1073

2) PXIe-1073 plus PXIe-1082 with PXIe-8360 controller

using a single laptop with 1 PCIe slot?

If yes, what additional hardwares do I need?

Thanks.

Best Regards,

karl

[MaggieAggie]

Hello KarlJason, 

1. It is possible to daisy chain two chassis and control them remotely from your computer. You can use the PXIe-PCIe 8372 to communicate from your PCIe slot to your first chassis. You will need an additional cable to connect between your chassis. However, depending on your system needs, ie. bandwidth, a different MXI cable may be a better choice.  

2. You can communicate between your laptop and the 1073. For the 8360, do you want to use the embedded controller, or still use the laptop as a remote controller? It is not possible to control a chassis with both a remote controller and an embedded controller. I can help you with the hardware if you can give me a better idea of what you are looking for.

[KarlJason]

Hi Maggie,

Thanks for the reply.  I only got a chance to read your reply today.

Anyways, my goal basically is this, the setup that we have currently in the lab is as itemized in my previous post.  Any of the engineers here can have either of the above setup but we have not tried it with both.  So the question is what if I need multiple modules on my setup for a short time only, can I use the systems that we already have installed rather than buying the chassis with more than 10 slots? If yes, how?

I'll only have 1 PC controller and that's a laptop.

As for the 8372, I still need further reading on it as I'm not so sure yet of what it does.  If how many of it do I need to control 2 chassis and how many if 3 chassis?  If the 8372 is like the PXIe-8110 then its not fully compatible to the way our systems are setup.

I'm also trying to find out here if what is the best possible expansion solution for us if modules are planned to be mobile from 1 setup to another and if multiple modules are needed for 1 setup (i.e., greater than 4 modules which the PXIe-1073 handles).  All these modules/chassis will have to be controlled by a laptop with 1 PCIe slot or by a PC with only one PCIe card.

Best Regards,

Karl

[MaggieAggie]

Hello KarlJason, 

Most laptops have an ExpressCard slot instead of a PCI slot. If so, you will need the PXIe-ExpressCard8360 to control your chassis. 

The 8372 allows you to connect to your computer via a MXI cable, as well as connect to the second chassis via MXI. The 8110 is an embedded controller, so it does not need a remote controller such as a desktop PC. 

Using the 8360, you can control multiple chassis with your laptop. However, you will be using a x1 MXI connection which will limit your bandwidth. To add on another chassis, you will need to connect to that chassis via a MXI cable as well. So, you are able to have multiple chassis' with many modules, but you are limited by the MXI bandwidth of theoretical 250 MB/s.

If you can give me some more information on what you want your system to do, I will be able to give you a better solution.