Chris, Could this be a mfg/assembly issue? I had a similar problem with a Virtex-5 design running across a backplane to an adjacent slot at 3.125 GHz. After isolating the problem to one board and which pair (rx or tx) was causing the errors, I had the board X-RAYed. Nothing looked wrong in the XRAY so I had the offending FPGA replaced. The problem went away. Perhaps my problem was a bad FPGA or a cold solder joint. Hope this helps. Ed > Date: Fri, 15 Jul 2011 10:09:12 -0400 > From: scott@xxxxxxxxxxxxx > To: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Xilinx IBERT Testing > > Chris > > Steve offered some good suggestions, but, you need to do some controlled > experiments. You didn't say whether your current experiments were with > just one channel running or all channels. I'm going to guess that you > have every channel running, since you said "links" in your description > of the problem. If that is a case, run the same experiments with only > one channel running. If that works, then your issue might be crosstalk > or power supply noise, both of which increase with increasing numbers of > transmitters. In that case you have lots of deep investigation to do. > > best regards, > > Scott > > Scott McMorrow > Teraspeed Consulting Group LLC > 121 North River Drive > Narragansett, RI 02882 > (401) 284-1827 Business > (401) 284-1840 Fax > > http://www.teraspeed.com > > Teraspeed® is the registered service mark of > Teraspeed Consulting Group LLC > > > On 7/15/2011 9:43 AM, Chris Johnson wrote: > > Steve, > > > > Thanks for your very thorough reply. It gives me a lot of things to > > look at. One thing that I noticed in getting to this point is that > > adding any pre/post-emphasis increases the BER. To me that indicates > > that channel loss would seem less likely to be an issue. Would you agree? > > > > Chris > > > > On 7/15/2011 1:19 AM, steve weir wrote: > >> Chris, the maximum run lengths of a given PRBSn pattern are: n 1's, and > >> n-1 0's. Failure of PRBS15/23/31 indicates that you have frequency > >> dependent distortions. Those could be coming from your channel, or from > >> your PDN. An brief list of things I would check first: > >> > >> 1. Tx eye quality. This will tell you if the problem is excessive > >> distortion and/or attenuation in the channel. > >> If the Tx eye looks good then you will need to look at the channel > >> > >> 1.S parameters on the channel from VNA or TDT measurements > >> 2. Preemphasis settings for the transmitter > >> 3. Equalization settings for the receiver > >> 4. AC coupling capacitor values and termination arrangement > >> > >> If the Tx eye is poor then you will need to look at the PDN and the > >> reference clock. > >> > >> PDN > >> 1. Tx driver PDN Z vs F > >> 2. PLL PDN Z vs F > >> > >> Reference clock > >> 1. Reference oscillator stability > >> > >> Steve > >> On 7/14/2011 9:53 PM, Chris Johnson wrote: > >>> I am debugging a board with a Virtex-6 HX380 chip and having some issues > >>> with getting low error rates using the Xilinx IBERT tool. I can tweak > >>> the MGTH parameters to have zero or near-zero errors for a PRBS7 > >>> pattern, but not for longer patterns, such as PRBS15/23/31. Is there a > >>> particular design flaw that is more likely to cause pattern sensitive > >>> failure for longer PRBS patterns, or could it be just about anything? > >>> The links are running at 10.3125 Gbps. > >>> > >>> Thanks, > >>> Chris > >>> > >>> ------------------------------------------------------------------ > >>> To unsubscribe from si-list: > >>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >>> > >>> or to administer your membership from a web page, go to: > >>> //www.freelists.org/webpage/si-list > >>> > >>> For help: > >>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >>> > >>> > >>> List technical documents are available at: > >>> http://www.si-list.net > >>> > >>> List archives are viewable at: > >>> //www.freelists.org/archives/si-list > >>> > >>> Old (prior to June 6, 2001) list archives are viewable at: > >>> http://www.qsl.net/wb6tpu > >>> > >>> > >>> > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List technical documents are available at: > http://www.si-list.net > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu