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Newbie shim
Newbie
133 Views
Registered: ‎02-01-2019

In-system logic analyzer

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I’m having issues setting parameters with an in-system logic analyzer. Vivado seems to set things up automatically and I would like to have a little more control. For instance in the eye scan attached (wall_eye.jpg) I can vary the differential swing down to 144mV, but I can’t see a difference between it and 566mV (setup in sweep_prop.jpg). I can’t trust the eye diagram since the ES_VERT_OFFSET is 8 bits which includes the values from -127 to 128, 256 codes and I think one code is 2 mv. So I expect that ES_VERT_OFFSET is covering 256*2=512mV. all eyes look relatively the same regardless of sweep settings. Could anyone steer me in the correct direction so I can understand what the tool is telling me or can control it better?

Using a Zynq Ultrascale+ in Vivado 18.2. I am “slightly” failing timing. This is a PCIe 3 connection so it goes through a link train so I don't know what the "User Value" even is. 

Thank you

Shim

wall_eye.jpg
Sweep_prop.jpg
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1 Solution

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Moderator
Moderator
51 Views
Registered: ‎07-30-2007

Re: In-system logic analyzer

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You must first pass timing.  Also be aware that there is an automatic gain stage that could fool you as well. although I wouldn't expect a good result from 144.  One of the assumptions is that the center of the eye is open.  If it isn't then your scan won't be valid.  It compares the reading at eye center to the off center reading.  If the eye is closed and the readings are the same then it will give a bad result.  You should try even higher swings as well as doing a loopback.

Roy


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2 Replies
Moderator
Moderator
52 Views
Registered: ‎07-30-2007

Re: In-system logic analyzer

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You must first pass timing.  Also be aware that there is an automatic gain stage that could fool you as well. although I wouldn't expect a good result from 144.  One of the assumptions is that the center of the eye is open.  If it isn't then your scan won't be valid.  It compares the reading at eye center to the off center reading.  If the eye is closed and the readings are the same then it will give a bad result.  You should try even higher swings as well as doing a loopback.

Roy


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Don't forget to reply, kudo, and accept as solution
----------------------------------------------------------------------------


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Newbie shim
Newbie
33 Views
Registered: ‎02-01-2019

Re: In-system logic analyzer

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Thank you for the responce.

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