How to automate Instantiation of modules in Verilog? (permutation)

Question

Consider this file tb_sr_latch.v:

`include "sr_latch.v"
module tb_sr_latch;
 reg [4:0] t_in;
 wire out;
 sr_latch M1(t_in[4], t_in[3], t_in[2], t_in[1], t_in[0], out);
 initial begin
 $dumpfile("tb_sr_latch.vcd");
 $dumpvars(0);
 t_in = 5'b00000;
 repeat(32) begin
 #1 t_in <= t_in + 5'b00001;
 end
 end
endmodule

there is a module instantiation which its name is M1, there can be other instantiation of this module to consider all possibilities and create all possible signals: for example for a module with 5 inputs it is possible to have 2^5 possibilities with (5! == 120) permutation ( because signals order matter) like:

 sr_latch M1(t_in[4], t_in[3], t_in[2], t_in[1], t_in[0], out);
 sr_latch M2(t_in[3], t_in[4], t_in[2], t_in[0], t_in[1], out);
 sr_latch M3(t_in[2], t_in[3], t_in[0], t_in[4], t_in[1], out);
 ...
 ...
 ...
 sr_latch M32(t_in[0], t_in[1], t_in[2], t_in[3], t_in[4], out);

Now my question is, is there any more pretty and automating way to do it?

• Tom Carpenter: generate for ... endgenerate

Answer 1

You can use several approaches to generate permutations, e.g. follow this link.

Using the above, the easiest is that you explicitly generate the instantiations for each permutation e.g. in Java (all 120 instantiations, exactly as you show in your example), write it into an include file, and in your program you just `include that file. Problem solved, no generate...endgenerate needed. You can also copy-paste, if you like your code in one file.

The other way is that you explicitly generate wire values for each permutation in Java, e.g.

wire [14:0] perm [0: 119]; 
assign perm[0] = {3'd0, 3'd1, 3'd2, 3'd3, 3'd4};
assign perm[1] = {3'd0, 3'd1, 3'd2, 3'd4, 3'd3};
assign perm[2] = {3'd0, 3'd1, 3'd3, 3'd2, 3'd4};
assign perm[3] = {3'd0, 3'd1, 3'd3, 3'd4, 3'd2};
// ...etc

then `include this or copy-paste into your main file, and you can use a simple generate..endgenerate structure:

genvar ii;
generate 
 for (ii=0; ii<120; ii=ii+1) begin: genblk
 sr_latch M(t_in[perm[ii][14:12]], t_in[perm[ii][11:9]], t_in[perm[ii][8:6]], t_in[perm[ii][5:3]], t_in[perm[ii][2:0]], out);
 end
endgenerate

Note that the instantiated devices are wrapped in genblk-s, so they are not named M1, M2, etc.

Finally, if you are a purist, you can take one of the algorithms (an iterative permutation calculator is the best) and implement them in Verilog. Waste of time, but nice fun. I don't recommend this though.