Parametrically sized localparam assignment

Altera_Forum · ‎05-10-2013

I would like to be able to assign an array of localparams with some kind of static function. For example I don't want to have to do this:


  localparam SIZE = 3;
  typedef logic  bar_t;
  localparam bar_t  FOO = {32'd1, 32'd2, 32'd3};

Because, while this works, it isn't fully parametric. I'd like to be able to do something like:


  localparam SIZE = 3; 
  typedef logic  bar_t; 
  function makeFoo (input integer size);
    bar_t  bar;
    integer i;
    for (i = 0; i < size; i++) begin
      bar = i;
    end
    return bar;
  endfunction
  localparam bar_t  FOO = makeFoo(SIZE);

Unfortunately, size inside of makeFoo isn't static (or at least Modelsim says it isn't).

Anyway, I'm wondering if anyone has a way to do this. I use static functions all the time to define simple localparam types, but this is proving more difficult.

Thanks,

Todd

Altera_Forum · ‎05-10-2013

So, to answer my own question, this appears to work, while not entirely elegant:

 
 `define MAX_BAR 128
  typedef logic  bar_t;
  function bar_t  makeFoo (input integer x);
    bar_t  bar;
    integer i;
    for (i = 0; i < x; i++) begin
      bar = i + 1;
    end
    return bar;
  endfunction
  . . .
  localparam bar_t  FOO = makeFoo(SIZE);

I'd like to be able to size everything only as large as I need it. But for static analysis, it's probably sufficient for most uses to set an upper bound like this.

Again, if anyone has a cleaner way to do this, I'd be interested to see it.

Altera_Forum · ‎05-10-2013

Try this:

module top;
   localparam SIZE = 3;
   typedef logic  bar_t;
   typedef bar_t  foo_t;
   function foo_t makeFoo;
      for(int i=0;i<$size(makeFoo);i++)
	makeFoo = i;
   endfunction
   localparam foo_t FOO = makeFoo;
   initial $display("%p",FOO);
endmodule

Altera_Forum · ‎05-10-2013

Thanks for the response. I tried your suggestion and I get this from Modelsim:


** Error: /some/file.sv(427): (vlog-2118) The function 'makeFoo' is not a valid constant function.
** Error: /some/file.sv(427): Parameter value must be constant.

I'm currently running:

Model Technology ModelSim DE vsim 10.1 Simulator 2011.12 Dec 5 2011

which is clearly a bit old, so I'm not sure if that's part of the problem. I know that Modelsim (along with Quartus) does multi-pass static elaboration, but apparently it's having a problem with that here.

Altera_Forum · ‎05-10-2013

You will have to show more code. The example I showed above works in ModelSim 10.1. It works all the way back to ModelSim 6.3 if you add ()'s to FOO = makeFoo();