Stats

  • State Not Answered
  • Replies 7
  • Subscribers 163
  • Views 3010
  • Members are here 0
More Content

Matched group - Analyze choses wrong pin pair target

Fredda

I have a matched group that seems to chose the wrong target pin pair when running the Analyze command. Is there a reason for not choosing the longest trace (DQ21)? See below screen capture.

By the way, how is the Delay column calculated?

/F

Parents
  • steve
    0

    THis could be related to the Pin delay which will add length to the pinpair. The tools take this into account when calculating a target value.

  • Fredda
    0 in reply to steve

    I never followed up on this two years ago, which I should have. Because I'm now facing the same problem again and I've forgotten how I solved it last time...

    This time I don't have any pin delay so couldn't be that. What I've noticed is that ETH_C_REF_CLK, which should be the target, has two vias in the trace and Allegro seems to have not included those vias in the length calculation when choosing the target.

    Can I manually choose a new target? I haven't found a way to do that.

    /F

  • steve
    0 in reply to Fredda

    Make sure you enable Z-Axis Delay (Setup - Constraints - Modes - Electrical) which should then take via length into account. If you want to set your own target then simply right click on the Delta:Tolerance column for the net you want as the Target. 

Reply
  • steve
    0 in reply to Fredda

    Make sure you enable Z-Axis Delay (Setup - Constraints - Modes - Electrical) which should then take via length into account. If you want to set your own target then simply right click on the Delta:Tolerance column for the net you want as the Target. 

Children
  • Fredda
    0 in reply to steve

    The Z-Axis Delay is activated and the length of the ETH_C_REF_CLK net is 25.314 mm, which includes the vias as far as I understand. The other value given for ETH_C_REF_CLK in the table, 22.284 mm should be the length without the vias and seems to be the value Allegro is using when setting the TARGET.

    I tried right clicking the Delta:Tolerance column to chose the TARGET, but couldn't see that it had an effect. It didn't seem to get updated properly. I will try again. Thanks.

  • Fredda
    0 in reply to Fredda

    So, I've got it working now. Not exactly sure what was going on, but I suspect Allegro is sensitive to in which order things are made. When I manually set the target to ETH_C_REF_CLK, the Delta:Tolerance column changed to TARGET, but the previous target still had the Actual column set to TARGET. Then when clicking on Analyze the Relative Delay column headers turned to yellow as if they were not being active. I ended up with removing the matched group and creating it again, which seems to have solved the problems.

  • avant
    0 in reply to Fredda

    After I make these kind of changes, I run a database check. Otherwise, the changes are not implemented correctly. 

  • jc teyssier
    0 in reply to steve

    Warning with this solution:

    Without target, all nets or pin pair in match group will have same length.

    example: 1mm; everyone will be between 1mm from all others maximum

    With target, all nets or pin pair in match group will have same length RELATIVE to the target

    So if a net is +1mm from target and an other one -1mm from target, then some nets can be 2mm from them in length.

    This is not the same result

Cadence Guidelines

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.