Two sdc files and one design

Hi Tsahi,

Typically, separate preCTS and postCTS files are used to adjust the values associated with "set_clock_uncertainty" and sometimes the set_min/max_delay values to account for propagated clocks.

However, in your case (thanks for the attachment, it is very helpful) it appears that the postCTS SDC contains the following types of additions:

1. Removal of "set_clock_transition" statements
   
   Removing these constraints should *not* be necessary in Encounter because
   postCTS the actual propagated clock values should override the SDC-asserted transition times.
   
   
2. Addition of "set_propagated_clock" statements
   
   Encounter will automatically append "set_propagated_clock" statements for each clock tree you build within Encounter. So long as your create_clock target == your AutoCTSRootPin, manually propagating the clocks postCTS with "set_propagated_clock" statements isn't necessary. If for some reason the create_clock target does *not* align with your AutoCTSRootPin, adding set_propagated_clock statements for each logical clock is necssary and may be why these are added.
   
   
3. A single addition of a set_clock_latency statement for one of the clocks.
   
   The postCTS SDC contains "set_clock_latency 2 [get_clocks wb_bus_clock]" so that the values in the postCTS file for set_min/max_delay statements are still valid when the internal clocks have been propagated.

Hope this helps,
Bob

You're welcome!

The first 2 items are minor (or perhaps meaningless depending on the caveats I mentioned in italics above). The 3rd item (set_clock_latency) is actually quite important and if not included it would invalidate your IO timing.

Thanks,
Bob

I just wanted to mention that the set_propagated_clock statements can also be important if you're not using Restore Design to bring your data up in Encounter. Most of the time, we read in verilog, def, and SDC (Import Design, defin, loadTimingCon) and if it's a postCTS design, we need to have the set_propagated_clock lines in the SDC file. So we always have a postCTS SDC file, even if that's the only difference. (We call the preCTS file design.ideal.sdc and the postCTS file design.prop.sdc.)