read_parasitics in PrimeTime

[childs]

Hi, can anyone help to explain more on the following options of the command "read_parasitics" in PrimeTime?
1. -complete_with -> PT will complete the incomplete annotation found. However, what is causing these incomplete annotation? Are we suppose to contend with the completion performed by PT or are we suppose to re-extract the parasitics?
2. -pin_cap_included -> I suppose this option will increase the accracy of the parasitics annotated, is this correct?

 

[birdy123]

Hi,

Please cehck the man page of this command in the Primetime...

Just for your reference , below is the details of these options.

-pin_cap_included

Indicates that the RC networks are to include the pin capacitances. By default, the RC network does not include pin capacitances. This option does not apply to the RSPF format. The RC pi model in RSPF format has to always include effect of pin capacitances.


-complete_with completion_type

This option does not apply to the RSPF format.

This option indicates that a net with partially annotated parasitics is to be completed by inserting capacitances and resistances according to the completion_type option. The allowed values are zero, which completes the net by inserting zero capacitances and resistances, and wlm, which completes the net by inserting capacitances and resistances derived from wire load models.

This option is equivalent to reading the parasitics file and then using the complete_net_parasitics -complete_with command.

Note: The complete_net_parasitics and read_parasitics -complete_with commands complete a net only if all missing segments are between two pins and the nets are partially annotated (nets are not affected if they are fully annotated or have no annotation at all). The net must also be hierarchical, so that if the parasitics for the block-level parts of a net are missing, those parasitics could exist in the top-level net. If any of these conditions are not met, you must manually correct the SPEF or DSPF file.

Still If you have anyconfusion please let me know.

 

[childs]

Thanks Bidy123, I have some questions extended as below:

-pin_cap_included
So i assume by including the pin capacitances, I shall be able to get more accurate annotation. (This question sounds stupid, but I just need to confirm )

-complete_with completion_type
What is normally causing the incomplete annotations in the parasitic file? Does such incomplete annotations mean the parasitic extraction or the design layout has problem?

 

[phoenixpavan]

Hey childs,

-pin_cap_included will get you more accurate annotation(Prime time userguide)
-complete_with completion_type since some nets may have their parasitics in a top level in a hierarchical design you may have to use this command....if that is not the case maybe now you have to verify your spef file and look for inconsistencies

 

[birdy123]

Hi ,

Oki one by one..

First of fall this is necessary that you should know how read_parasitics read a SPEF(or any other format of parasitic file). When reading parasitics files, PrimeTime assumes by default that capacitance values specified in the SPEF files do not include the pin capacitance. The pin capacitance values used by PrimeTime are the values specified in the Synopsys design libraries; any pin capacitance values specified in SPEF are ignored.
So if you will add pin_cap_included option then during read_parasitic it will read the pin capacitance and your final capaacitance will include this also. So you can say that you are getting more accurate annotation. But doing this will increase your runtime and memory also.

Now lets talk about the complete_with option:
Some it happen that your SPEF file has incomplet RC network for particular nets. When the network is incomplete PrimeTime discards the RC network information but instead uses the total capacitance specified in the SPEF for the net. Therefore, the net will have lumped capacitance and resistance but not an RC network. So during reading such SPEF files you will receive warning message "The specified net has an imcomplete RC network. This means that some RC elements are dangling, or that all drivers and loads of the nets are not connected by all the RC
elements. The RC network annotation is ignored for the specified net."

Similar things can happen for Pins also.You receive this message if the read_parasitics command has found the specified pin in theparasitics file but not in the designfile;therefore, read_parasitics cannot annotate the associated net. Possible causes for this error could include spelling errors or typos, or writing the parasitics file and the design file from different
versions of the design.

So in short it doesn't mean that your design has some problem or prasitic extraction has some problem. It can both or may be none (just missmatching in version). So for this you have to check the design or version of the parasitic file.
Rest is clearly mention in the above discription of the command ( -complete_with completion_type).

I hope this much will help you.

 

[phoenixpavan]

good explanation birdy...