Verilog array of different sized vectors

Question

I have a problem that requires converging wires down in stages, where each stage has half as many inputs and outputs as the previous one (think similar to staged selectors). I don't want to have unconnected wires in my module.

Can I declare an array of size numStages of vectors, and then define the size of each vector in a generate loop? For example:

module Log2Alg(x, a, b);
    parameter N = 1;
    localparam numStages = $clog2(N);
    output x;
    input [N-1:0] a, b;
    wire [???] stageInputs [0:numStages-1];
    wire [???] stageOutputs [0:numStages-1];

    genvar i, j;
    generate
        for(i = 0; i < numStages; i = i + 1)
        begin: generateStage
            stageInputs[i] = [2**(N-i):0]; // ???
            stageOutputs[i+1] = [2**(N-i-1)-1:0] // ???

            // Do stuff. Loop over j = i**2-1:0
        end
    endgenerate

endmodule

Is there another approach I should be considering, or a way to accomplish what I am attempting?

Why not define the wires inside generate block? So that you can adjust the wire dimensions and you can access if as if it was an array. (E.g. generateStage[3].stageInputs) — Alper Kucukkomurler
– Alper Kucukkomurler, Commented Feb 9, 2017 at 7:15
Can you merge 2 output wires of a stage or all outputs are different? And how many stages do u have? — Karan Shah
– Karan Shah, Commented Feb 9, 2017 at 13:53

dave_59 · Accepted Answer · 2017-02-09 21:51:43Z

2

You can move the declarations of your wires into the generate loop instead of making them arrays.

module Log2Alg #(N=1) (
    output x, 
    input [N-1:0] a, b
    );
    localparam numStages = $clog2(N);


    genvar i, j;
    generate
        for(i = 0; i < numStages; i = i + 1)
        begin: generateStage
        wire stageInputs [2**(N-i):0];
        wire stageOutputs [2**(N-i-1)-1:0];
            // Do _stuff_. Loop over j = i**2-1:0
            //
        end
    endgenerate

endmodule

Then if you need to access wires in a different stage from the current stuff, you can use something like generateStage[i+1].stageInputs. The index you use access generateStage must be a constant because it's not really an array of identical elements.

answered Feb 9, 2017 at 21:51

dave_59

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2 Comments

Joshua W Over a year ago

Follow up question: Is there any way I could create or access an implicit generateStage[-1]?

dave_59 Over a year ago

You can start the generate loop at -1. You can also put conditional generates around the stuff code.

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