RocketIO signal polarity swap

I'm planning on using the TXPOLARITY and RXPOLARITY attributes in the RIOs on a Virtex-II Pro device (via Aurora cores) to swap the function of the N and P lines in order to help improve the path of PCB tracks to an edge connector.

Has anyone used this polarity swapping capability before? Does it work OK? Are there any "undocumented features" or pitfalls that I should know about before designing the board in this way?

TIA,

Rog.

There is no difference when asserting the TXPOLARITY and RXPOLARITY inputs on the Virtex-II Pro MGTs other than a logical inversion of the data stream to accommodate P/N pin swaps. The Aurora core includes detection logic in the receiver portion and will automatically switch the RXPOLARITY state if it needs to in the initialization state.

The only "pitfall" to watch for is to make sure that you properly document your schematic so that when someone else picks it up a few years down the road they know that you did this intentionally and don't curse your name after spending 3 weeks debugging why the link didn't work.

Ed McGettigan

-- Xilinx Inc.

Excellent answer. I'll design it in now.

Thanks.

Roger.