Xilinx Boards and Kits

[solonor2011]

Hi everyone,

I have a question about connecting two ML605 over GTX running Aurora protocol (Xilinx example design). Here are the the configurations that I have tried:

1- Connect two ML605s using the GTX SMA connectors that are on the board. (5 GHz)

2- Connet two ML605S + XM104 Connectivity Kit (FMC) using SMA connectors that are on the FMC card (5 GHz)

3- Connet two ML605S + XM104 Connectivity Kit (FMC) using SATA connectors that are on the FMC card (3.125 GHz)

Let's first talk about cases 1 and 2. In both case the link comes up. In case 1, I can reliably run without any BER but in case 2 I get random bit errors. I have tried this with different combinations of 4 boards that I have, and, in case 2, only one combination could run without any errors. Case 1 is completely reliable for all the combinations.

Case 3, which is running slower (3.125 GHz), works reliably for all the boards.

My questions is that, should I expect a more unreliable connection when I'm using an FMC card? Does the extra connector cause signal integrity and bit error issues?

Thanks,

Amir

[mcgett]

Your case #2 will have more loss in the communication channel due to the FMC connectors and additional PCB trace on the modules.  Using different settings for the TX swing, TX pre-emphasis, and RX equalization will improve the BER for this link.

BTW, your line rates are actually Gbps and not GHz.

[solonor2011]

Thanks for the reply. That was my mistake, I meant Gbps not GHz.

Should I just increase the TX Swing (set to 810mv right now)?

Could you please give me some hints or point me to a document about how to set these three values for better signal integrity?

Thanks,

Amir

[solonor2011]

I increased the TX pre-emphasis (TXPREEMPHASIS set to 2.77) and also voltage swing (TXDIFFCTRL set to 1180mv) to max. I definitely get less errors but still errors are pretty frequent.

1- Are there any other parameters that I should tweak?

2- Should I also change TXPOSTEMPHASIS? 

It seems that I should use IBERT to tune these parameters. Right?

Thanks,

Amir

[mcgett]

> It seems that I should use IBERT to tune these parameters. Right?

Yes, IBERT is the best way to optimize the link.

One other item to look at is the construction/length of the coax cables that you are using to ensure that there are no issues.