Help needed for few Physical Design question ?

Hello , I am new into Physical Design . I have few questions regarding it , whom answers i didn't got. ... please help me out and excuse me if my questions are not upto standards .

I am working/training on an design called ORCA. We have been given specifications ... I have few doubts regarding that ..

1) The core utilization %age is 80% ... so how do we calculate it ... why is it 80 % ...

2) Target IR drop is 10% of supply voltage ? I asked many but answers i got was :-( ... why isn't 12% or 8% ... how to come up to this %age figure ...

3) when i increased core utlization area to 90% , my macros got placed outside core area ... ????? ... so does it mean that increase in core utilization area decreases width and height ? ...

4) why do we remove all placed standard cells , then write out floorplan in DEF format ... what's use of DEF file?

5) Can area recovery be done by downsizing cells at path with high timing slack (+ve) ...

I hope above questions are relevant and upto standard of EDAboard.

Hai jeet_asic,

1. core utilization percentage is fixed based on needs.. Normally 70 t0 80 percentage.. Remaining percentage will be go for routing..

if u fixed as 80% means then the utilization should be

80% of utilization = (total area) * 100/80

2. Some times Ir drop will be higher than 10%. if IR drop is lower than 10% it doesnt matter.. but sometimes higher inthis case we need take care of it.. This 10% is based on ur design and customer requirements.

Note core utilization(80%) and IR drop(10%) is not accurate its just an approximate target which we work on..

3. If u go on with 90% then there may be a problem of conjestion and routing problem. It means that u can,t do within this area.. Sometimes u can fit within 90% utilization but while go on for timing optimization like upsize and adding buffers will lead to increase in size.. so in this case u cant do nothing so we need to come back to floorplan again.. So to be on safer side we are fixing to 70 to 80% utilization..I think u may got a bit..

4. DEF deals only with floorplan size... So to get the abstract of the floorplan we are doing like this.. saving and loading this file we can get this abstact again.. we dont need to redo floorplan..

5. ya sure.. Also deleting unwanted buffers will also help in area recovery...

Dont think about standards jeet. we are here to learn.. dont underestimate urself..
really ur questions r valuable..:-D

Every question is WORTH asking.

Thanks sir for reply. really helped me. We can manipulate IR drop by changing number of power straps. I increased my power straps which reduced my IR drop , but how many power straps can i keep adding to reduce IR drop ? how to calculate number of straps required. what problems can arise with increase in number of straps ?

Hai jeet_asic,
We can use tools to calculate this IR drop(ex:- voltage strom) if drop is high...based on that we can add stripes.. but if u do a projects repeatedly u will come to know that this much straps is enough.. In this case u will not need tools.. Its having calculation but its not accurate its an approximate one..

Number of straps will create problem in routing also it affects area.. So results will be in routing congestion..