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TCL based assertion for connectivity check

harsharaj

Hi,

 I am using ncsim and i wish to check connectivity between two nets in RTL/netlist using tcl. I remember there being someway where using tcl input file i could specify two nets which could be tested for connectivity.

ex:
 -src net1  -dst net2

on a change of net1 check net2 value is equal to net1 value. kind of an tcl assertion

I dont remember the syntax. kindly help

thnaks!
Harsha

  • You could do this using a breakpoint, something like:

    stop -create -object net1 -execute { if {#net1 != #net2} {puts "error net1 != net2"}} 

    However if you have a lot of these the simulation will be slow, and it doesn't guarantee that your connection is correct. You cannot even tell if the check was made, so there will always be doubt as to how well you verified your connection.

    If you have access to Incisive Formal Verifier (IFV or IEV) then you can use the Formal Connectivity Check app to make point-to-pint connection checks and formally prove them. This avoids the performance penalty of simulating the design, it gives you complete visibility via coverage, and ensures that you cannot get false passes. The connections are entered in a spreadsheet format and code is generatd from that, taking into account muxes etc.

    Here's a link to a webinar we did on the subject, you can register and watch the recording: http://www.cadence.com/cadence/events/Pages/event.aspx?eventid=466

     

  •  Thanks Stephen,

     But it looks like "puts" is not recognized by irun/ncsim

     ncsim: *E,TCLERR: invalid command name "puts "error mismatch on net"".
    invalid command name "puts "error mismatch on net""

     

    any suggestions ?

  •  okay i got the 'puts' working.

     what i need now is to start this check on every change of net1 value. will the below get the job done ?

     

     stop -continue -object tb.inst1.net1 -execute { if {#tb.inst1.net1 != #tb.inst1.net2} {puts "*E ERROR mismatch "}}  

     

    Thanks.

  • One thing to watch out for: this will fail if you have any propagation delays between the two nets. Stopping on net2 might avoid that. Overall I still would not recommend this simulation-based technique; it was the best one could hope for 15 years ago but formal technologies make this push-button now, and give you a proff, not just a bit more optimism. :-)

  •  Hey thanks. I will have a look at the webinar :-) 

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