How to instantiate module with variables

Question

I declared alu_result as a reg because I need it to be a variable data type for my case statement. But when i do this, I cannot pass it my write_data in my datapath_tb module. Is there some work around where I can get this to work?

module alu(input [31:0] input1, input2, input [2:0] control);
parameter SIZE=32;
reg [31:0] alu_result;
reg overflow;
always @(*)
begin
 case(control)
 0: alu_result = input1 & input2;
 1: alu_result = input1 | input2;
 2: alu_result = input1 + input2;
 3: alu_result = (input1 < input2)?1'b1:1'b0; //unsigned, no additional bits to worry about
 4: alu_result = input1 ^ input2;
 5: alu_result = ~(input1 | input2);
 6: alu_result = input1 - input2;
 7: alu_result = (~(input1 + 1) < input2)?1'b1:1'b0; //2's comp is ~ & +1
 default: alu_result = input1 & input2;
 endcase
 
 if(alu_result > 32'hFFFFFFFF)
 begin
 overflow <= alu_result;
 end
end
endmodule // alu

module datapath_tb();
parameter SIZE = 32; 
reg clk;
reg write;
reg [4:0] write_addr;
reg [31:0] write_data;
reg [4:0] read_addr1;
reg [4:0] read_addr2;
wire [31:0] read_data1;
wire [31:0] read_data2;
// Instantiate the register file
Register rf_1 (.clk(clk), .write_en(write), .write_addr(write_addr), .write_data(write_data), .read_addr1(read_addr1), .read_addr2(read_addr2), .read_data1(read_data1), .read_data2(read_data2));
// Instantiate the ALU
alu #(SIZE) alu_1 (.input1(read_data1), .input2(read_data2), .alu_result(write_data)); //Line in question
// Create a clocking signal
 always begin
 # 10;
 clk = 1; 
 # 10;
 clk = 0;
 end 
 initial begin
 // Write DIGIT0 into register 0
 
 // Write DIGIT1 into register 1
 end
endmodule

Answer 1

Declare your module ports as:

module alu #(parameter SIZE=32) (input wire [SIZE-1:0] input1, input2, 
 wire [2:0] control, 
 output reg [SIZE-1:0] alu_result,
 reg overflow );

• TheBigBoyOverThere: That actually worked. Though I moved out control and overflow to declare locally. Now I'm just working on connecting it correctly on my datapath_tb module. "alu_result Must be connected to a structural or net expression" Thanks for your help.