Parameter inside a module inside a module

Question

I have read about parameters and how to redefine them at module instantiation, but what if I have a parameter inside a module inside a module? Say that I have a small module called gen:

module gen(input,output);
parameter n=2;
parameter m=10;
//do something
endmodule

That module is instantiated in another module called top:

module top(inputs,output);
gen gen1(inputs,output);
//do something
endmodule;   

I am trying to make a testbench on the big module where I need to redefine the two parameters n and m:

module tb;
reg input;
wire output;
top top1(input,output);
endmodule

How can I do that?

Answer 1

One solution is to redefine the parameters at each level:

module gen(input,output);
parameter n=2;
parameter m=10;
//do something
endmodule


module top(inputs,output);
parameter n=2;
parameter m=10;
gen #(.n(n), .m(m)) gen1(inputs,output);
//do something
endmodule

module tb;
reg input;
wire output;
top #(.n(n), .m(m)) top1(input,output);
endmodule

Another solution is to keep your current module definition and use defparam in your testbench to hierarchically override the value of parameters:

module tb;
reg input;
wire output;
defparam top1.gen1.m = 4;
defparam top1.gen1.n = 5;
top top1(input,output);
endmodule