I m not even sure what tool you re supposed to use for that

Question

I m not even sure what tool you re supposed to use for that magic doesn t seem to know anything about SPEF The pic above suggests DEF2SPEF but I can find nothing like that

Nickson Jose · Answer

I think this is one of the limitation as of now just remembered this mention from Prof < mshalan> s openlane introductory video

tnt · Answer

Yeah but I would assume there is already tools to do that and they re just not plugged into the flow yet Pretty sure I saw a talk about the raven and they were talking abot post route STA and SPEFs

Nickson Jose · Answer

Thanks for the info < tnt> I could generate spef outside openLane using def2spef utility

tnt · Answer

There is a def2spef Where did you find that

Nickson Jose · Answer

tnt · Answer

Mmm yeah looking at it it s not particularely inspiring tbh seems a lot of hand parsing generation rather than rely on good known LEF DEF parsers is not a great first sign

Nickson Jose · Answer

True < tnt>

mshalan · Answer

< Nickson Jose> Consider this instead This is the one used by OpenLane Both developed by my students

Nickson Jose · Answer

Thanks < mshalan>

Nickson Jose · Answer

Hi < mshalan> which lef file would be the input to this extractor tech lef or merged lef While using the tlef file I m getting the attached error

Ahmed Ghazy · Answer

< Nickson Jose> It is complaining that it can t find the cell so use the `merged lef` which contains both tech information and the cells

Nickson Jose · Answer

< Ahmed Ghazy> It worked thanks

Nickson Jose · Answer

Hi < Ahmed Ghazy> < mshalan> i m running post routing STA in openSTA using the SPEF generated from above extractor im getting below 2 warnings while executing read spef command also there s no effect of parasitics showing up in the slack calculation i e with or w o SPEF the slack value is same

mshalan · Answer

< Nickson Jose> Can you share the SPEF file

Nickson Jose · Answer

Hi < mshalan> I have compressed the main file it was around 30 MB

Nickson Jose · Answer

Hi < mshalan> could you make anything out of the SPEF file

mshalan · Answer

Hi < Nickson Jose> changes have been committed to fix the extractor Please try again

Nickson Jose · Answer

Ok will try and let you know

Nickson Jose · Answer

Hi < mshalan> im caught in a situation here

Nickson Jose · Answer

My objective is to compare the slack values pre and post layout

Nickson Jose · Answer

For pre layout STA im using synthesized netlist for analysis and for post Im using pre route netlist + the generated SPEF file but my post layout setup slack is greater than pre layout one which doesn t make sense am I missing something here

tnt · Answer

The openlane pre layout STA uses estimates for the load capacitance so those can be overestimated

Nickson Jose · Answer

< tnt> ok so that justifies it

Nickson Jose · Answer

< tnt> so if i need to do a fruitful pre and post STA analysis what modifications do I need to do

tnt · Answer

Not sure what you mean by fruitful First my above statement is just a theory possible explanation but still there could be other issues in the pre post route STA causing them to not be accurate Second you need an estimate of the driving slew rate and load capacitance to make timing estimates that have any basis in reality The liberty file contain infos delays for different data point of drive slew and load capacitance so you need to provide that For pre layout STA you need to come up with something to plug in there AFAIU

mshalan · Answer

< tnt> < Nickson Jose> pre routing STA is based on RC estimates for the interconnects OpenROAD app creates virtual routes and uses only one metal layer parameters to calculate the delays If you are using the OpenROAD App you may influence this by using the command ```set wire rc layer metal layer name```

mshalan · Answer

< tnt> lib file contains wire load models WLM which can be used to estimate the interconnect RC values even before PnR Plave and ROute

tnt · Answer

it does I couldn t see anything from a quick glance at it

mshalan · Answer

There is a default WLM which is used by OpenSTA You may pick a specific wire model based on the design size

tnt · Answer

I thought that was coming from the techlef not the cell library lib

mshalan · Answer

To instruct OpenROAD App to use the tech LEF info use the command I posted above

Nickson Jose · Answer

< mshalan> as per my understanding openlane is wrapper around openroad so where do I make the definition for set wire rc in openlane

mshalan · Answer

Hi < Nickson Jose> OpenLANE is a flow methodology that uses open source EDA tools including OpenROAD Check OpenLANE base sdc

Nickson Jose · Answer

HI Prof < mshalan> I couldn t find the WLM in the lib file can you specify where does openlane fetch that info from

Nickson Jose · Answer

im only using sky130 fd sc hd pdk

Nickson Jose · Answer

Hi < mshalan> I m facing below error while generating spef file from the above SPEF EXTRACTOR I m attaching the lef and def file for reference too

Nickson Jose · Answer

Start parsing LEF file Parsing LEF file done Start parsing DEF file Parsing DEF file done Parameters Used Edge Capacitance Factor 1 Wire model PI Traceback most recent call last File main py line 482 in lt module gt firstLayer = lef parser via dict myVia layers 0 KeyError via2 FR

Nickson Jose · Answer

lef def tar gz