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Use of array inside a loop in SPECTRE

wang159

If I declare an array in SPECTRE, for example:

>> electrical [1:10] var;

and I use it inside a loop:

>> for (index = 1; index <=total; index=index+1) begin

>>     if (index > 1) begin

>>         I(var[index],var[index-1]) <+V(branch)*R;

>>     end

>>     else ........ (omitted)

>> end

This gives me an error indicating the index of var is out of range. I suspect the origin of this error is SPECTRE checks the validity of index by substituting it with initial and final index values of the for loop. The "var[index-1]" thus becomes "var[0]" when index=1. However, this will never happen, since it is within a if statement. 

I am wondering what is the best solution to resolve this issue. Is there a way that SPECTRE can ignore checking the index range to bypass this error?

Thanks for the help!

  • Your example wasn't complete - I assume index is a genvar. Anyway, assuming that it was, then with genvar the loop is effectively unwrapped so that it generates contribution statements per index of the for loop - and this is done at compile time rather than run time (in essence). So that means that it will still generate a statement (albeit within the if) with an invalid array bound in the contribution statement. The solution is to write it differently:

        for (index=2; index<=10; index=index+1) begin
            I(var[index],var[index-1])<+V(sig)*R;
        end
        // put else part here

    Regards,

    Andrew.

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