length matching across groups of nets

For your last statement where you clear the target and it keeps coming back: If you have a Delta value that is any value other than null, a target is required. The target can be defined by you or generated by the system but it is required for a Relative Prop Delay case. When the delta value is null, it's a Match Delay case.

If you are in 16.0 or later and XL or higher, you can make use of the Avanced Constraints feature to either use a formula on the MG constraint value or use a formula to constrain the length of the target you set for Group C based on A + B. There is a tutorial on this feature in your hierarchy: << install_dir >>\doc\cmadvcnstut

If you don't want to/can't use Advanced Constraints, route and fix the targets for A & B and then constraint the length of the target for C with whatever the sum of their lengths are (use min/max prop delay with a built in tolerance for the min/max values).

 Regards,

-Dennis

I'm running 16.2 with the performancre option only.

You say constrain the length of the target for group C with min/max values. I see how this works but it looks like I need to remove all group C nets from rel prop delay and enter the min/max values for them. I guess this could also be done with a total etch length group.

So the sum of A + B = 4395.02

I have all group C nets with a min/max of 4390/4400.

Sounds good, thanks for your help.

It would be a matter of prefernce I guess: either put the same min/max rule on all of group C or just make sure the target of group C is the right length and then match all of group C to that target.

 -Dennis