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.altergroup usage question

GaneshShamnur

Hi All,

I want to use altergroup in the below scenario of a spectre netlist.

------------------------------------------------------------

<netlist_section>

...

I1 (a1) MyCell1
I0 (a1 0 0 0 0 0) MyCell2

tran1 tran stop=10n write="spectre.ic" writefinal="spectre.fc" \
    annotate=status maxiters=5

...

altTest altergroup {

// I0 (a1 0 0 0 0 0) MyCell2 ( Works well simulating 2nd analysis tran2!)
 I0 (0 a1 0 0 0 0) MyCell2  //(This fails !)
}

tran2 tran stop=10n write="spectre.ic" writefinal="spectre.fc" \
    annotate=status maxiters=5

------------------------------------------------------------

My intension in trying the above scenario is to change the netlist connection for I0 from 1st-pin[i.e I0(a1 0 0 0 0)] to 2nd-pin[i.e I0( 0 a1  0 0 0)] 

Spectre errors out complaining about a connection happening to different node in comparison to earlier definition !

 

I have also tried another option where the whole subcircuit for I1 instance was redefined in altergroup. This failed too !

Any ideas on how to achieve my objective ?

Thanks,
Ganesh
 

  • Hi All,

    I figured out solution to my problem although, it wasn't achievable via altergroup since Spectre-Altergroup( current latest revision as of this writing) doesn't natively support netlist topology modifications.

    Below were two solutions:

    1)  Refer to the link to replicate the suggested method:http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:ViewSolution;solutionNumber=11002322

    2) Include some parameterized components ( e.g: switch/resistor) and control their parameter values in altergroup. Thereby select an appropriate connection.

    e.g: The above problem was solved for first two pins with below netlist, assuming the other 3 pins were grounded. If we were select amongst the other three pins aswell, we need additional 3 pins.

     ------------------------------------------------------------

    <netlist_section>

    parameters sw1=1 sw2=0

    ...

    I1 (a1) MyCell1

    I2 (a1,out1) MySwitch1 // This switch is ON only when sw1=1 and OFF when sw1=0

    I3 (a1,out2) MySwitch2 // This switch is ON only when sw2=1 and OFF when sw2=0

     

    I0 (out1 out2 0 0 0) MyCell2

    tran1 tran stop=10n write="spectre.ic" writefinal="spectre.fc" \

        annotate=status maxiters=5

    ...

    altTest altergroup {

    parameters sw1 = 0 sw2 = 1

    I0 (out1 out2 0 0 0) MyCell2 

    }

    tran2 tran stop=10n write="spectre.ic" writefinal="spectre.fc" \

        annotate=status maxiters=5

    ------------------------------------------------------------

     Both have pros and cons to each method.

    1st method would need netlist-modification and oceanscript creation. But the flow can be automated.

    2nd method is additional components insertion into design. But this flow has cleaner netlisting mechanism.

     

    Regards,

    Ganesh 

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