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Why did the post-layout simulation result incorrectly?

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nxthuan512

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Hi,

I am working on the full digital implementation using Synopsys/Cadence tools.

The implementation steps include: (1) Synthesized by Design compiler -> (2) Simulated netlist by VCS -> (3) Place&Route by IC Compiler -> (4) Simulated ICC file by VCS -> (5) DRC/LVS/Antenna check by Calibre -> (6) Simulated spice file of LVS by nanosim -> (7) Extracted C and RC by starrc -> (8) Simulated C extracted file by nanosim -> (9) Simulated RC extracted file by nanosim.

Steps (1) to (8) delivered correct results (log files) and waveform. The simulation results of LVS and C extraction were also correct. However, the simulation results of step (9) was incorrect.

Could you please give some solutions for this problem, e.g. what step should I check again etc.

Thank you very much
 

nxthuan512 said:
Hi,

I am working on the full digital implementation using Synopsys/Cadence tools.

The implementation steps include: (1) Synthesized by Design compiler -> (2) Simulated netlist by VCS -> (3) Place&Route by IC Compiler -> (4) Simulated ICC file by VCS -> (5) DRC/LVS/Antenna check by Calibre -> (6) Simulated spice file of LVS by nanosim -> (7) Extracted C and RC by starrc -> (8) Simulated C extracted file by nanosim -> (9) Simulated RC extracted file by nanosim.

Steps (1) to (8) delivered correct results (log files) and waveform. The simulation results of LVS and C extraction were also correct. However, the simulation results of step (9) was incorrect.

Could you please give some solutions for this problem, e.g. what step should I check again etc.

Thank you very much
Click to expand...

Did you perform RC extraction during (3) with the same effort as in (9)?
 

ThisIsNotSam said:
Did you perform RC extraction during (3) with the same effort as in (9)?
Click to expand...

Hi,

Thank for your reply. I am not sure yet.
(3) P&R was done by ICC and the extract command is extract_rc
(7) was done by Starrc by the command StarXtract
(9) was done by Nanosim with default settings.
Please let me know your thought? Thanks.
 

my thought is you made a mistake in (3) and performed a "preroute effort" extraction
 

When you say the result of (9) was "incorrect", does
that mean "not as wished" or does it mean "provably
false, by some valid comparison"?

Many people many times are unhappy with what post
route simulations reveal. This does not mean the result
is wrong. Rather, it means either expectations or
implementation (or modeling*extraction) are.

Step back and contemplate the nature of "incorrect".
Maybe this alone suggests next steps.
 

dick_freebird said:
When you say the result of (9) was "incorrect", does
that mean "not as wished" or does it mean "provably
false, by some valid comparison"?

Many people many times are unhappy with what post
route simulations reveal. This does not mean the result
is wrong. Rather, it means either expectations or
implementation (or modeling*extraction) are.

Step back and contemplate the nature of "incorrect".
Maybe this alone suggests next steps.
Click to expand...

Hi, the result of (9) was completely false (wrong function), as compared to (8). Because all the previous steps produced correct results, I didn't know why (9) failed. Thanks.
 
Last edited by a moderator:

I guess I'd start with looking at race conditions and
timing hazards, at or just before the point where the
two simulations' results diverge.
 

(8) Simulated C extracted file by nanosim -> Simulation result is correct.
(9) Simulated RC extracted file by nanosim -> Simulation failed.

If your extraction procedure is correct, can you find the difference in extraction output data ? ( I mean this can be written to SDF file ect..)
As to simulation "failed", what is the failed phenomenons ? Is it X propagation ? is it mismatch in output and expected value ?
 

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