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Clock to Pad Timing warning: 1 Constraint Failed

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sivarajm

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Hi...
I have to design a one code (VHDL), to operate in 200MHz. I have returned the code. My target tool is Vertex 5. While given the constraints in ISE, i am facing the problem.
3 options are der for clk:
Period:
pad to setup:
clk to pad:
For all the three options I gave 5ns. After place and route, I got
"1 Constraint Failed" as warning. I have attached the message which i am getting.

Can u tell me why it is occurring and how to overcome this problem?
 

Clock to Pad Timing?

Imo you've to really understand what are theese values.

I mean:
Period is 5ns because your clk runs to 200Mhz and that's ok
Pad to setup and clk to pad are the timing you've to define in order to have hold and setup time that are ok with your external speification if pad is the pin out of the FPGA, whereas if it's internal I hope that you can assign the default that is ok for your family (I don't like very much xilinxs).

Told that the problem could be for example a bad routing driven by a huge fanout pins (and if that's the case you can duplicate your source signal) or bad routing because you've a lot of combinatorial logic between source and sink (and in that case you should consider if you can pipeline your signal) or also the source signal is generated by a different clock than the clk of the sink..

Welcome in the FPGA/Asic timings :)
 

Re: Clock to Pad Timing?

Actually i uploaded one image but I think it didnt properly uploaded...k any how...

"1 Constraint Failed" as warning. Here the thing which i am getting

Met : No
Constraint : Offset=out 5ns After Comp ”clk”
Check : Max Delay
WorstCase Slack : -3.536ns
Best Achievable: 8.536ns (Note: Exceeding 5ns)
Time Errors: 20
Timing Score:68025

The above is only for offset out, for remaining 2 is k.

Can u tell me why it is occurring and how to overcome this problem?
----------------------------------------------------------------------------------------------
hi pini_1, i gave constraint like "global"
 

Clock to Pad Timing?

Hey u can see that there is negative slack. So there is setup violation. U need to avoid that. try again by giving different values till u get a 0 or positive slack.
 

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