I'm trying to length match a group of nets to the sum of two other groups of nets. Can't seem to figure it out.
Group A - target = 1203.91
Group B - target = 3191.11
Group C - target = 1818.20
Group C must match A + B
I added a delta of 2576.82 to group C, and cleared the "target" field but the target keeps coming back when that group is analyzed.
Any help is appreciated.
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).
In reply to Dennis Nagle:
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.
In reply to padmaster:
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.