SDF entries and their correlation with timing?

[vaidyseenu]

Hi,

I have been trying to establish the correlation between, SDF entries and their corresponding timing reports. My question basically has two parts:

1) How are the entries for SETUP and HOLD are determined in SDF?
2) For a specific instance if there is a negative value associated with the SDF entry, can that be associated with the corresponding instance's slack in timing reports?

 

[Mina Magdy]

Hi vaidyseenu,
SPF(standard parasitic format) describes interconnect delay and loading due to parasitic resistance and capacitance.
https://iroi.seu.edu.cn/books/asics/Book2/CH17/CH17.4.htm
look at section 17.4.1

1)the Setup and hold are usually determined by using the SDF file on Timing tool , the tool will calculate the timing according to sdf file for any hold violation and according to the frequency constrain it will calculate the the slack and if there is any setup violation (-ve slack).
2) i didn't face that before and i am not much expert so i couldn't help.

 

[dave_59]

SDF values are usually calculated by one of two ways: 1) estimates from synthesis tools based on actual gate characteristics and statistical models for gate placement and layout. 2) Actual calculations from the layout tools.

SDF values may be negative for one of three reasons: 1) The simulation models already contain delays and the SDF is used to to adjust those delays +/-; not replace them. 2) Path delays are computed in segments, and the way the calculation is split up, some parts of the path might wind up with a negative delay, but the total path delay will add up to a positive delay. 3) Setup/hold times depend on the layout of a flip-flop and the relative amount of delay included in the data and clock paths inside the cell.