What are the differences between SDF versus SPEF?

[daffo123]

SDF versus SPEF

I forgot the differences between SDF and SPEF.

Pls.... Someone tells me the difference.

According to my old memories...

SDF has only cell delay and spef has RC interconnection delay...

I want to know....
Please let me know the truth.

Thanks in advance.

 

[shelby]

SDF versus SPEF

SDF has actual delays for cells and nets in ps (max/min and rise/fall).

SPEF has resistance and capacitance values for nets (split iton segments). The delay calculator inside the sta tools use SPEF + .libs to calculate the delays

 

[w1yu77]

Re: SDF versus SPEF

Hi, shelby.
What algorithm does the delay calculator of commercial tool like Astro of Synopsys use for net delay? Is it just Elmore?
I used Astro for timing report before routing. But found the delay number different from that obtained with Elmore and R and C's in SPEF output. :|

Many thanks!

SDF has actual delays for cells and nets in ps (max/min and rise/fall).

SPEF has resistance and capacitance values for nets (split iton segments). The delay calculator inside the sta tools use SPEF + .libs to calculate the delays

 

[shelby]

Not sure what delay models they use , but ...

Pre-route timing does not use extracted RCs based on the pdk tech files. What it will do (i think) is a simple steiner route (ignoring shorts) and then use the capTables to look up estimated RC values on the nets.

This is normally fairly accurate (within 5% or so). If not you can create a extracted spef and then correlate it with your estimated spef. You can then using scaling factors to get your estimated RCs to match the extracted ones.