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Using int and max functions in an instance property of a schematic pcell

prasadtammana

Hi, 

I've written a skill code to create schematic pcell by following the code Andrew mentioned in the below post: 

https://community.cadence.com/cadence_technology_forums/f/custom-ic-skill/42256/how-to-disable-enable-a-device-in-schematic-pcell-while-netlisting

After I create an instance, I wanted to replace its property named "fingers" using the command below. 

dbReplacePropList(instId list( list("fingers" "string" "int(pPar(\"Length\")/0.84)")  ))

But LVS run is failing saying "int" function is not allowed. I would like to use max function in another case. Could you please let me know if we have any alternative commands that I can use inside pcDefinePCell function to get int and max of pcell variables? 

Thanks,

Prasad

Parents

  • Prasad,

    There are two issues at play here. First of all, expressions on instances are supposed to be in "AEL" (Analog Expression Language) syntax, and in theory (although not always in practice) those should get translated into supported functions for the specific netlist language. AEL doesn't have int, but it does have floor and ceil (to round down and round up). Spectre supports floor, ceil and also int. min and max are not AEL functions, but Spectre does support them. The second issue is which LVS tool you're using - because unless that supports the functions you're hoping for then this isn't going to work. 

    Which LVS tool are you using?

    The alternative is that rather than putting the expression on the instance, you have your PCell code evaluate the expression. The downside of that is that the Length parameter on the instance of your component (the component you have the schematic PCell) will have to be a fixed number and can't be an expression or passed parameter (the reason being that the netlister would need to netlist each hierarchical occurrence of the pcell instance separately to get the correct expansion of any pPar's further up the hierarchy, and that's not supported as it would get rather complicated).

    Regards,

    Andrew 

Reply

  • Prasad,

    There are two issues at play here. First of all, expressions on instances are supposed to be in "AEL" (Analog Expression Language) syntax, and in theory (although not always in practice) those should get translated into supported functions for the specific netlist language. AEL doesn't have int, but it does have floor and ceil (to round down and round up). Spectre supports floor, ceil and also int. min and max are not AEL functions, but Spectre does support them. The second issue is which LVS tool you're using - because unless that supports the functions you're hoping for then this isn't going to work. 

    Which LVS tool are you using?

    The alternative is that rather than putting the expression on the instance, you have your PCell code evaluate the expression. The downside of that is that the Length parameter on the instance of your component (the component you have the schematic PCell) will have to be a fixed number and can't be an expression or passed parameter (the reason being that the netlister would need to netlist each hierarchical occurrence of the pcell instance separately to get the correct expansion of any pPar's further up the hierarchy, and that's not supported as it would get rather complicated).

    Regards,

    Andrew 

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