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Cannot call pPar for CDF parameter

farhan89

Hello,

I wrote a pcell for layout and Symbol view for nmos. There are only 2 parameters that user can define (W and L). These CDF parameters have simple call backs functions to check that value in non zero. When I place the instance of nmos symbol in another schematic and edit the parameters at pPar("W") and pPar("W") then I get the error that:

*WARNING* cdfiSetParamValueOnInst: Could not get a float from property 'W' on instance 'I2'

CDF: An error occurred when evaluating callback.

Callback: W->callback => CheckLW(cdfgData->W)

Message: *Error* eval: undefined function - pPar


I tried changing the formal parameters of symbol view as:
 (
        (W           string   "75e-6"     ) ;; Channel Width
        (L            string  "20e-6"     ) ;; Channel Length
    )

but still it doesn't accept the input as pPar. Can anyone help me what should I modify in CDF parameters to make pPar work ?

My CDF parameter code
    cdfCreateParam( cdfId
        ?name "W"
        ?prompt "Channel width"
        ?defValue "100e-6"
        ?type "string"
        ?display "t"
        ?parseAsNumber "t"
        ?units "lengthMetric"
        ?callback "CheckLW(cdfgData->W)"
        ?storeDefault "yes"
    ?parseAsCEL "yes"
    )
    cdfCreateParam( cdfId
        ?name "L"
        ?prompt "Channel length"
        ?defValue "20e-6"
        ?type "string"
        ?display "t"
        ?parseAsNumber "t"
        ?units "lengthMetric"
        ?callback "CheckLW(cdfgData->L)"
        ?storeDefault "yes"
    ?parseAsCEL "yes"
    )

Thanks

Farhan

Parents

  • Hi Farhan,

    OK, several things here:

    1. Do you really need your symbol to be a pcell - that's relatively unusual (does it change the symbol dependent upon the parameters?)
    2. It looks as if the main problem is that your callback is trying to evaluate the value of the CDF parameter (at a guess - you didn't show what that function does). This is doomed to failure - see this article on the Dangers of CDF callbacks
    3. pPar in general is fine - just you can't expect the callback to be able to evaluate it - you'd typically have to ensure that it just tolerates it, or write a PDK that doesn't depend on CDF callbacks to derive values. If your callbacks are just checking values (as the name suggests in your case), then they could just suspend doing that check if it looks like an expression of some sort - i.e. isn't a literal value.
    4. You should give your callback function a name that distinguishes it from other functions - e.g. a unique prefix.
    5. The ?parseAsNumber argument values should be "yes" not "t".

    Regards,

    Andrew

Reply

  • Hi Farhan,

    OK, several things here:

    1. Do you really need your symbol to be a pcell - that's relatively unusual (does it change the symbol dependent upon the parameters?)
    2. It looks as if the main problem is that your callback is trying to evaluate the value of the CDF parameter (at a guess - you didn't show what that function does). This is doomed to failure - see this article on the Dangers of CDF callbacks
    3. pPar in general is fine - just you can't expect the callback to be able to evaluate it - you'd typically have to ensure that it just tolerates it, or write a PDK that doesn't depend on CDF callbacks to derive values. If your callbacks are just checking values (as the name suggests in your case), then they could just suspend doing that check if it looks like an expression of some sort - i.e. isn't a literal value.
    4. You should give your callback function a name that distinguishes it from other functions - e.g. a unique prefix.
    5. The ?parseAsNumber argument values should be "yes" not "t".

    Regards,

    Andrew

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