Question about calculating final data required time

[downloadman]

Hi,

I have observed in most of the pdfs that to calcuate final data required time, clock uncertainity (clock skew) will be subtracted from the clock period(cycle adjust) and clock network delay(source latency) is being added.

Most of the times, source latency is defined as 0, but clock skew should be added to the capture clock edge.
Can any one clarify on this?

 

[phoenixpavan]

Re: [Clock Arrival Time]

Hi downloadman,

Source latency is the same for both launch and capture flops...this is the case for flops in a single clock domain...whereas skew is difference in arrival times of the clock at the launch and capture flops through the network...so if the capture is receiving clock late it will be added to clock period, else it will be removed from clock period...

cheers,

 

[downloadman]

Re: [Clock Arrival Time]

Hi Pavan,

Thanks for the reply.
In the report i have seen, if i have defined skew using the folloiwng command
set_clock_uncertainity 0.1 [all_clocks] -- this means it is positive or negative skew ???

In the timing report, while calculatng data required time, this is getting subtracted from the clock period. Is it expected behavior??

 

[phoenixpavan]

Re: [Clock Arrival Time]

Hi downloadman,

if you are doing post-cts analysis ur clock uncertainty doesn't include skew and if it is pre-cts analysis it will be subtracted from the clock period and it is expected behavior of the analysis

useful??

 

[downloadman]

Re: [Clock Arrival Time]

:smile:

Thanks for the reply.
Your reply answered my question.