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Regarding Physical Library

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praneshcn

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Hi ,

Why is tat lef format is recommended for macro physical lib info and gdsii format for standard cells. wat r advantages and disadvantages between lef and gdsii.

thankz.
 

vlsitechnology

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LEF is physical information tht is library exchange format which consist of a design rules..for a metal layers, vias, antenna rules and abstract view and so on..
Macro lef is also the same thing....
u will have to analyse the advantage of this...bcz answer is with u by reading this

But GDS2 consist of physical information and it comes out only whn ur design is complete or if ur designing a std cell or if ur doing a designing project such as PCI or ethernet controller then after completion of the design u need to convert it to gds2 so that fab people convert this to tape out and then finally for procesing of the layers...
 

praneshcn

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hi,

still didnt get the point completely. could u eloborate plz?
 

shankarmit

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Hi,

macro Lef contains physical dimension of macro and layers and pin dimensions.

When u do place and route. U need only physical dimension and pin layer pin locations , u dont need internal wells until u dump out final gds2.

So they use lef for macros.. and one more this This macros comes in GDS2 to us for P&R. Extracting pin layer pin location pin size from GDS2 will take time instead u can use the Lef directly and while final dumping out GDS2 use the macro GDS2 for tapeout.

hope u understand,if not let me know.

Thanks
Shankar
 

praneshcn

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Hi sankar,

One thing i understood was we need just the pin location, dimension and layer and the physical dimension of the macros for p & r and hence we use macro lef which is more compact. but u have mentioned tat for tape out we need to use macro gdsii. while library preparation we import only macro lef where does macro gdsii come into pic.

Also standard cell lef also contain pin definitions so why not use it instead of std cell gdsii.


thankz.
 

shankarmit

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praneshcn said:
Hi sankar,

One thing i understood was we need just the pin location, dimension and layer and the physical dimension of the macros for p & r and hence we use macro lef which is more compact. but u have mentioned tat for tape out we need to use macro gdsii. while library preparation we import only macro lef where does macro gdsii come into pic.

Also standard cell lef also contain pin definitions so why not use it instead of std cell gdsii.


thankz.

Hi pranesh,

I hope u understood what is lef and gds2. so u itself can think can we tapeout a design with only lef. We need gds2 of all macros for tapeout right?. Check in your library preparation script, U will use lef for extraction FRAM view in synopsys flow but u will stream in the gds as CEL view. Which flow u use?

Why lef is not used for standard cells?...stdcell lef contains stdcell dimensions, pin layer pin location right? But u will never block routing over stdcell right.. so if u use only lef how can u see internal metal1 layers inside the stdcell. So only u will use gds2 so that router will see inside metal1 routing and will route accordingly to avoid drc violations.

In case of macros, u will block routing over the macros.expect some top layers..(as there is no routing inside macros with this top layers). so in this scenario, only lef is enough as router is going to route means it going to connect only pins of the macros.

Hope u understood, with only lef u cant streamout all the layers right...


Thanks

Regards
Shankar
 

vlsitechnology

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Hi shankar this gds2 comes only after completion of ur design am i right?
when u import the design also u wil have gds2 that is right but that is for the macro and std cells....
But actuall gds2 will come out after the completion of our design right?
 

shankarmit

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vlsitechnology said:
Hi shankar this gds2 comes only after completion of ur design am i right?
when u import the design also u wil have gds2 that is right but that is for the macro and std cells....
But actuall gds2 will come out after the completion of our design right?

yes ur r right... u will have gds2 of macro and standard cells..
then after completing design u will dump out final design gds2 for tapeout.
 

vlsitechnology

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Does anyone have any idea about the strategy of nanoroute?
 

praneshcn

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Hi
Is it possible to do p&r without gdsii. for a design consisting of 50k std cells, i used only std cell lef physical lib and completed p & r flow (i.e., till detailed routing). I met timing and had some drc, lvs violations which i corrected in the p &r tool itself. i used magma flow. i am of the view tat gdsii is required for doing physical verification. please correct me if i am wrong.


Also one more common question for i didnt get an exact answer is " Why do we have drc and lvs violations when we do a physical verification process say on a tool like hercules while those violations are not shown by the p & r tools.


thnx
 

Ash_ali

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hi,

Definatelly u can do P&R with out GDSii. The gdsii file needed for doing P&R is of standard cell library, that thing u got it from lef. so that thing worked.

When u do Physical verification, basically u r checking DRC & LVS ,ERC etc.
for that u need GDSii of your completed design i.e design for which u have done P&R.

Basically these checks will compare Layout and your netlist for LVS,
Design rules such as spacing and overlapping etc for DRC.

Hope now your clear why the tool is asking for GDSii file after P&R to do physical verification.

For ur second question,

In the P&R tool we check for top layer.

where as Hercules & other physical verification tools checks violations for all the levels or layers.

Hope u r clear now.

regards
Ashfian
 

jprathapkv

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GDS2 has more physical layers such as Diffusion Layers--

LEF libraries have less info..suitable for Macros if they are used as Black boxes..
 

kumar_eee

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LEF contains pin info & metal layers that are used in std cell Layout. We are using this because the data base size is very less compared to GDSII format database. And to add, you don't need any basic layer( NW, OD, PP, Poly,NP) info to do P & R.

All physical verification tools takes GDSII as a input format to check the DRC/LVS violations. Thats why we are exporting the design into GDSII format to check the violations.

Hope this helps.. If not, please let me know..
 

Amruth

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GDSII contains cell views & poly information right
thats y v require it to do DRC/LVS
but LEF dont have this information
 

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