How skew and latency numbers are set for CTS stage?

[tachyons]

Hi All,


1) What is the pre requisites to start CTS stage ? How do you generate the cts tech file?

2) On what basis skew and latency numbers are set for building a CTS? how
are they calculated and given as a spec to the CTS tool ?

3) What are the different metrics you look at to qualify the CTS ? Explain in detail the need for each metrics you look at to qualify CTS? what are the trade-offs you can do between the metrics you use to qualify CTS ?

Regards
Tachyons

 

[phoenixpavan]

Re: Queries in CTS stage

Hi tachyons,

Prior to CTS the design should be

1. Placement completed
2. Power and ground nets should be routed
3. Congestion and timing analysis should give acceptable results
4. No cap/tran violations
5. HFNS completed
6. All clocks are defined and No propagated clocks


For skew/latency numbers

the tool calculates the skew values by comparing the arrival times of the clock signals in a clock domain..if you do not specify max skew it will be considered as "0".
Similarly the insertion delay will be checked after synthesizing the initial clock tree to meet the min value if not buffers will be inserted to meet the value.Default is "0".
Balancing of Skew is the most important metric for qualifying CTS

cheers,
Pavan GS

 

[tachyons]

Re: Queries in CTS stage

Hi Pavan,

Thanks for the reply. How is skew numbers and insertion delay numbers arrived in the constraint development stage which comes as an input the back end implementation for building CTS? On what factors it depends? Does it depend on clock freq? design? If so, how is the relation defined?

Regards
Tachyons

 

[jeevan.life]

Prior to CTS you have your global routing model...Based on the values from global routing you get the necessary values..