[SOLVED] Problem during inserting buffer on clock net

[ramesh28]

Hello all,

i'm using Olympus SOC pnr tool from mentor graphics.

i'm getting error while inserting buffer on clock net. As i want to insert buffer on clock path to fix hold violation.

command using is:

create_buffer -libcell $libcell -pin $pin

Can anyone help me out why i'm getting error while inserting buffer?

Thank you...

 

[alam4vlsi]

What error you are getting?

 

[rca]

Normaly the tool adds buffer on data path to fix hold time violation, no?

- - - Updated - - -

generaly we avoid to touch the clock network after the clock tree, no?

 

[ramesh28]

Thanx rca,

i'm confused about where to add buffers. Ya ur right.

That means we normally dont touch the clock network after cts. right?

 

[rca]

yes we should avoid to modify the CTS after clock tree.

 

[ramesh28]

Hi rca,

just one query, while adding buffers, which location we have to prefer? i mean towards launch flop or towards capture flop?

thanx.

 

[rca]

first, the optiminsation phase post CTS should fix the hold time, righ?
at least you could add an incremental post-CTS hold time optimisation if the first one does not resolve every thing.
take care also to fix the setup and trans/cap before fixing the hold time after CTS.

Minus violation could be (generally) handle with the post-routing optimisation.

 

[ramesh28]

Thanx rca.

i got that.. But my question is while fixing hold, we should add buffer at D pin of flop (towards capture flop) or we should add buffers at Q pin of flop (at launch flop)..
i'm asking this bcz in case of common paths, which may gets affected by adding buffers..so i think we prefer adding buffer at capture flop. am i right? correct me if i am wrong.

 

[rca]

yes you should add the buffer close to the D pin.
but normaly the tool should handle that, and you do not need to insert manually the buffer.

 

[ramesh28]

Thank you rca, for useful suggestion..