make_case_tb.v

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// baeckler - 05-05-2006
// 
// This is a trick to generate case statements / LUT masks
// from an existing comb circuit.  It's handy when the structure
// of the current implementation is getting in the way.
//

module make_case_tb ();

`include "log2.inc"

localparam IN_WIDTH = 4;
localparam OUT_WIDTH = 8;
localparam LOG_OUT_WIDTH = log2(OUT_WIDTH-1);

reg [IN_WIDTH-1:0] in;
wire [OUT_WIDTH-1:0] out;

///////////////////////
// target function
///////////////////////
// drive all inputs from IN
// merge all outputs to OUT.
bin_to_asc_hex ba (.in(in),.out(out));
	defparam ba .WIDTH=IN_WIDTH;

///////////////////////
// sim loop
///////////////////////
integer n,k;
reg [(1<<IN_WIDTH)-1:0] tmp_mask;
reg [LOG_OUT_WIDTH-1:0] tmp_out;
wire [IN_WIDTH-1:0] max_mask = (1<<IN_WIDTH)-1;

initial begin
	
	////////////////////////////////////////
	// make a case statement
	////////////////////////////////////////
	$display ("// case statement version");
	$display ("case (in)");
	for (n=0; n<(1<<IN_WIDTH); n=n+1)
	begin
		in = n;
		#5
		$display ("    %d'h%x : out = %d'b%b;",
			IN_WIDTH,in,OUT_WIDTH,out);
	end
	$display ("endcase\n");
	
	////////////////////////////////////////
	// make a look up table for each output
	////////////////////////////////////////
	$display ("// look up table version");
	for (k=0; k<OUT_WIDTH; k=k+1)
	begin
		tmp_mask = 0;
		tmp_out = k;
		for (n=0; n<(1<<IN_WIDTH); n=n+1)
		begin
			in = n;
			#5
			if (out[k]) tmp_mask[n] = 1'b1;
		end
		$display ("wire [%d:0] mask%d = %d'h%x;",
			max_mask,tmp_out,{1'b0,max_mask}+1'b1,tmp_mask);
		$display ("assign out[%d] = mask%d[in];",tmp_out,tmp_out);
	end

	$stop();
end

endmodule