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Explorer
Explorer
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Registered: ‎08-31-2017

Question about the timing report

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Hi, 

I have two questions about the timing path report.

Q1: In the set up timing path report, it shows the "Clock Path SKEW" is 4.970ns and clock uncertainty is 0.3ns. However, in the path report, I don't see where it use the figure for path delay calculation but clock uncertainty. Thus, what does it show in the timing report?

 

Q2: In the case, it has set up time violations. The number of falling endpoints are 4. The total number of endpoints are 8. I'm curious what's the definition of the total number of endpoints shown here. What does it mean ? Or what document can I check for details since I'm wondering why it is 8 instead of more.

Thanks

All the best,

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Explorer
Explorer
419 Views
Registered: ‎07-18-2018

Re: Question about the timing report

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@nanson,

Do this, in the report_timing_summary Window select a large number. Like 500 for each highlighted:

ENDPOINTS.PNG

It will then report more in the report timing summary.

How many endpoints do you expect to have in your design? It looks like you have a BUS of at least 30 wide.

For this question: From Selection_137 & Selection_138, I don't see where it use Clock Path Skew 4.97ns in calculation. That's my question

If you hover over the number at the top of the report it should show you a window:

CPSE.png

Those will have the numbers and equation used to cacualte it.

It looks like this is an input with just a DST clock path, which means there is no CPR or SCD. So it's just the Clock delays:

 

MATH.PNG

Which gives you the 4.97 you are seeing. It isn't "used" because it is summerizing the difference between the two clock paths. It's already built into the timing check as it cacualtes those clock path fields.

4 Replies
Explorer
Explorer
438 Views
Registered: ‎07-18-2018

Re: Question about the timing report

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@nanson,

Can you share either the reports or screen shots of what sections you are looking at. It would be helpful.

But a non specific answer to the question based on where I think you might be looking at:

1. The Path in the Clock portion should have a Clock uncertanity, and a Clock Pessimism. The CPR is the pessimissim portion from the Clock Path Skew Equation.

The skew is the difference from the Source clock (add all the delays together) and the Dst clock (add them all together) minus the difference where they share a common node. So it's already being accounted for. It's only the removal of where the difference in clock paths between them that gets used in addition.

2. I am assuming you did something like:

report_timing -from [<START PATH>] - to [<END PATH>] -nworst 50 -max_paths 50 -delay_type min_max -name RESULTS

Which should show all the possible timing paths. Which will give you the Slow and Fast Process corner for setup and hold, and also the possible rise and fall edges. So there might be a lot of potential timing arcs depending on the path that are checked, but only some may be failing timing. The tool only reports out the worst numbers it finds. If thats not what you are looking at, a screen shot of what number of end points you are looking at can help know.

 

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Explorer
Explorer
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Registered: ‎08-31-2017

Re: Question about the timing report

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@evant_nq 

Thanks for your time for the comment.

Selection_134 : As you can see, it shows the number of endpoints is 8. I'd like to trace why is eight.

Selection_136: After clicking the open the implemented timing report in Selection_134, it pops up the path information for the 8 paths.

Selection_137: I just click the path 1 in Selection_136 and it shows the detailed path information. In this figure, you can see the Clock Path Skew is 4.97ns.

Selection_138: From Selection_137 & Selection_138, I don't see where it use Clock Path Skew 4.97ns in calculation. That's my question. 

Selection_134.png
Selection_136.png
Selection_137.png
Selection_138.png
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Explorer
Explorer
420 Views
Registered: ‎07-18-2018

Re: Question about the timing report

Jump to solution

@nanson,

Do this, in the report_timing_summary Window select a large number. Like 500 for each highlighted:

ENDPOINTS.PNG

It will then report more in the report timing summary.

How many endpoints do you expect to have in your design? It looks like you have a BUS of at least 30 wide.

For this question: From Selection_137 & Selection_138, I don't see where it use Clock Path Skew 4.97ns in calculation. That's my question

If you hover over the number at the top of the report it should show you a window:

CPSE.png

Those will have the numbers and equation used to cacualte it.

It looks like this is an input with just a DST clock path, which means there is no CPR or SCD. So it's just the Clock delays:

 

MATH.PNG

Which gives you the 4.97 you are seeing. It isn't "used" because it is summerizing the difference between the two clock paths. It's already built into the timing check as it cacualtes those clock path fields.

Explorer
Explorer
405 Views
Registered: ‎08-31-2017

Re: Question about the timing report

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@evant_nq 

Thanks for your kindly guidance. 

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