instantiating a module inside an always block

Question

I am just starting to learn verilog, so this may be a very basic question, but i couldn't really understand or find an alternative to express my intentions in verilog.

I will take a smaller example. I am basically trying to connect the output of one of my modules to input for another. Please help me with line mark 49 and give an alternative to it.

   25 module ands (
   26     input1,
   27     input2,
   28     outputs
   29 );
   30     input [2:0] input1;
   31     input input2;
   32     output [2:0] outputs;
   33 
   34     integer itr;
   35 
   36     and a (outputs[0],input1[0],input2);
   37     initial
   38     begin
   39         for (itr = 1 ; itr <= 2; itr = itr+1)
   40             and a(outputs[itr],input1[itr],outputs[itr-1]);
   41     end
   42 
   43 endmodule

I know it is a stupid example and i can easily avoid using the for loop, but i want to actually later use parameters.

Thanks, and sorry if it is just too basic.

A related question on [module instantiation](http://stackoverflow.com/q/20066850/97073). — Morgan, Nov 25 '13 at 07:37

score 6 · Accepted Answer · answered Nov 25 '13 at 05:38

Verilog modules are not intended to be instantiated inside of initial or always blocks. If you want to instantiate multiple modules with a loop, then the generate block is what you want to use. Using your example:

module ands (
    input1,
    input2,
    outputs
);
    input [2:0] input1;
    input input2;
    output [2:0] outputs;

    integer itr;

    and a (outputs[0],input1[0],input2);

    genvar itr;
    generate
        for (itr = 1 ; itr <= 2; itr = itr+1)
            and a(outputs[itr],input1[itr],outputs[itr-1]);
    endgenerate

endmodule

This requires using verilog2001 or later.

Should the `integer itr;` not be removed? – Morgan Nov 25 '13 at 07:39 — Morgan, Nov 25 '13 at 07:39

score 0 · Answer 2 · answered Nov 25 '13 at 05:36

0

You need to use genvar itr and a generate ... endgenerate block instead of an initial block. This should do exactly what you want.

answered Nov 25 '13 at 05:36

alex.forencich

1,187
8
16

instantiating a module inside an always block

2 Answers2