MXI-Express RIO Frequently Asked Questions (FAQs)


This tutorial goes over some of the frequently asked questions regarding the NI MXI-Express RIO expansion chassis.


Q: How many chassis can be daisy chained?

A: The number of systems that can be daisy chained is system-dependent, and is influenced by the host OS/BIOS and the PCI Express host architecture. Based on testing, you should be able to daisy chain four to seven chassis, depending on your system. Each string of daisy-chained chassis will be limited to the bandwidth of a x1 PCI Express lane (250 MB/s theoretical).

See the Developer Zone Tutorial: System Configuration Effects on NI MXI-Express RIO Daisy Chain Depth for more details.

Q: Can I synchronize multiple chassis?

A: Yes, but not natively. The system clock is not exported on the MXI-Express bus. To synchronize multiple chassis, use digital input/output (DIO) modules and the field-programmable gate array (FPGA) to create a system-wide clock.

Q: How many chassis can I connect to one host controller?

A: The maximum number of chassis is OS/BIOS-dependent, and depends on the number of PCI Express bus segments in the system. A single device consumes multiple segments (MXI-Express RIO uses four whereas MXI-Express host cards use three). The maximum number of bus segments allowed by the PCI Express spec is 255, although some PC vendors make assumptions in their BIOS to limit the number based on its design assumptions. 

Assuming the PC BIOS supports up to 255 bus segments, and that the controller takes about 30 bus numbers for other devices, the maximum recommended configuration is eight daisy-chained lines of six chassis each, for a total of eight MXI adapters and 48 MXI-Express RIO chassis. This configuration should use (48 MXI-Express RIO) * (4 bus segments per  MXI-Express RIO) + (8 chassis) * (3 bus segments per MXI-Express host card) + (30 reserved bus numbers) = 246 of the 255 PCI Express bus numbers.

Q: Which controllers are compatible with MXI-Express RIO?

A: MXI-Express RIO is compatible with the following:

  • Both real-time and Windows controllers
  • NI 9081/9082 multicore NI CompactRIO
  • NI 3100/3110 industrial controllers
  • NI 835x rack-mount controllers (integrated MXI-Express interface)
  • NI PXI/PXI Express controllers using the NI PXIe-ExpressCard8360 or the NI PXI/PXIe-8364
  • Third-party PCs with a PCI Express MXI-Express adapter
  • Third-party laptops with ExpressCard MXI-Express adapter
  • MXI-Express RIO is also compatible with third-party controllers that meet OS/BIOS requirements and that contain the right port to accept a MXI-Express interface. For details on compatible third-party PCs, see the Developer Zone Tutorial: PCI Express Clock Specifications and Effect on NI MXI-Express RIO Interoperability.

Q: Can I use the NI PXI/PXIe-8360 MXI adapter?

A: No, the NI PXIe-8360 X1 MXI-Express for PXI Express interface is a slave-only device, meaning you cannot use it from a PXI host controller to connect to a MXI-Express chassis. To use MXI-Express RIO with your PXI or PXI Express chassis, you need to use the NI ExpressCard-8360 or NI PXI/PXIe-8364.

Q: How do I know if my configuration could max out the MXI-Express bus throughput when streaming data?

A: You have to calculate the maximum data throughput rates from each module in the system, as well as take into account which chassis in the daisy chain contains the modules. Attached below is a system configurator spreadsheet, which you can use to calculate maximum allowable throughput numbers for a specific system.

Note: This spreadsheet gives you a good approximation, but was calculated based on benchmarks from a specific hardware configuration. Actual throughput numbers from your system are dependent on the host OS, BIOS, and software architecture used to stream data.

Q: Am I limited to three DMA FIFOs between the controller and a MXI-Express RIO daisy chain?

A: With MXI-Express RIO, you can have up to three DMA FIFOs per chassis in a daisy chain. So, if you have three chassis daisy chained together to a host, you can have three DMA FIFOs per chassis for a daisy chain total of nine DMA FIFOs.

Q: What happens to the rest of the system when I disconnect or lose power to a MXI-Express RIO chassis?

A: The MXI-Express RIO device and any downstream devices can detect that there has been a communication loss with the host and chose to either power down or continue to run LabVIEW FPGA code. If a MXI-Express RIO device loses power in the chain, any devices downstream of it would detect that the host went away. In either case, the upstream devices will remain connected provided the host PC does not blue screen from the unplugging/power-down event.

Q: What’s the max cable length?

A: The max cable length is seven meters between each chassis. For a longer distance distributed solution, use the NI EtherCAT RIO or NI Ethernet RIO expansion chassis, which allow you to reach distances of up to 100 meters before a hub or repeater. For even further distances, consider NI wireless sensor networks (WSNs), which allow you to reach distances up to 300 meters between nodes.

Q: Is the RIO Scan Engine supported?

A: No, the FPGA must be accessed and programmed with the NI LabVIEW FPGA Module.

Q: Is there a fiber MXI-Express option?

A: No, this has been a common point of feedback and is under review.

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