1.6 GB/s per-slot PXIe bandwidth

[mgoldman5]

We are trying to select a PXIe system to house an AWG we are going to evaluate.  The AWG (Keysight M3202A) will support 1.6 GB/s (4 lanes) bandwidth when used with a Gen 2 PCIe link and 400 MB/s (1 lane) when used with a Gen 1 link.  We would like to take full advantage of this bandwidth.  We will probably have a few other cards in the chassis as well, but nothing that will require appreciable bandwidth.

The PXIe/PCIe-8381 controller pairing seems best, as that will give us 8 lanes of Gen 2 bandwidth from the PC to the PXIe chassis.  My question mostly concerns the chassis itself.  The PXIe-1082 is most cost-effective; we need an external clock input, eliminating more basic models.  The problem is that it only supports 1 GB/s per-slot bandwidth.  Where is the bandwidth limitation?  From the 1082 manual, it seems that the controller slot has a direct x4 link to slot 2.  If we put the AWG in slot 2 and left all other slots empty, why could we not achieve the full bandwidth (1.6 GB/s) of a x4 Gen 2 link?  The PEX8612 switch seems to be a Gen 2 device, which seems to imply that the chassis lanes should support Gen 2 speeds.

Thank you for any help you can give.

[TylerC1123 · Accepted solution]

Hi mgoldman5,

You are correct that the PXIe-1082 is a Gen 2 device, and that Slot 2 on the chassis has a direct x4 link to the controller.

The device does however support "Up to 2 GB/s (single direction) per PXI Express slot dedicated bandwidth (x4 PCIe)" - from the PXIe-1082's User Manual. The device's total bandwidth is 8GB/s, and this is divided between the 4 links, with 2GB/s each. The first link as you noted is dedicated to Slot 2, so that slot will support the full 2GB/s for any card placed in it.

For the other 3 links, they handle two slots on the chassis each and thus the total bandwidth for that link will be split between it's slots according to priority of the device placed in them through the PEX8612 Switch.

This is best illustrated by Figure 1-3 in the PXIe-1082 User Manual

Regards,

[mgoldman5]

Thank you for clearing that up!