Can you use multiple processors in a PXI chassis?

[broskyar]

Can I use a dedicated processor board to control a serial communications module in a PXI system? Can I put a processor in any module slot? Are there jumpers that distinguish between system controllers and non-system controllers like in VME?

[David S]

Hi broskyar,

While PXI does have many of the same features as VXI and VME, this is one feature that is different. According to the PXI specification, the system controller must be in slot 1. This means a device can only be controlled by a system controller in slot 1.

The PXI backplane has three different types of slots. Slot 1 is the system controller slot, slot 2 is a timing and synchronization slot, and the rest of the slots are peripheral slots. Each type of slot is wired a bit differently. Normally, embedded PXI and CPCI embedded computers are designed to be system controllers and can only work in a system controller slot. These computers may boot in a non slot 1 slot, but they will not have access to the PXI backplane.

In short, if you do plac
e a second embedded computer in your PXI system, it will not be able to directly control any other module in your PXI system.

Regards,

David Shatila
Applications Engineer
National Instruments

[broskyar]

Well, what if I had a second controller running say Windows 2000. Would I be able to call NI-VISA functions to access the CSRs? Does the use of NI-VISA require access to the PXI backplane?

I have a feeling that the second controller would cause the system to lock up upon booting up. If a boot of both controllers was successful, I don't believe that two MAXs running at the same time would work out.

I wonder if there would be any other way to access the CSRs?

[David S]

Hi broskyar,

Even if you use NI-VISA, the second controller would still need to use the PXI backplane to communicate with your PXI module. According to the PXI specification, only the controller in slot 1 will be able to control the PXI backplane. Because the slots are wired differently, a controller in any slot besides slot 1 would not be able detect or control any PXI device. Adding a second controller is not a supported feature of PXI or CPCI.

If you design and build a custom embedded PXI computer and a custom CSR, it may be possible to use the local bus to communicate between your devices. There may also be third party devices that could solve your problem. For information on third party devices and on the PXI specification, I recommend
you visit the PXI Systems Alliance at www.pxisa.org.

Regards,

David Shatila
Applications Engineer
National Instruments

[Greg Caesar]

Since PXI is based on PCI, PXI defines only one system controller per PXI system. But there are other options.

PXI is compatible with CompactPCI, and some CompactPCI suppliers, such as Inova, provide "slave CPU" modules for CompactPCI. Just be aware that communication between the slave CPU module and other PXI/cPCI peripheral modules is not the same as a PC or PXI embedded controller, so you may have to implement your own drivers.

Another option are FPGA or DSP boards for PXI/CompactPCI. For example, the National Instruments PXI-7831R has a LabVIEW-programmable FPGA with 8 analog inputs, 8 analog outputs, and 96 digital lines - all independent or capable of being synchronized. One typical application of this board is implementation of custom communicatio
n protocals with the 96 digital lines.