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I am using task in my module in verilog coding, and facing problem, in passing the argument values. actually The variables defined in the task block as input are not receiving the values that are passed to them while calling this task. Here is the code

module carry_addr(Cin,A,B,Sum, Cout,rst_n );
parameter width=3;
parameter bits=1;
input [width:0] A,B;
input Cin,rst_n;
output reg [width:0] Sum;
output reg Cout;
integer k;

reg [width+1:0]C2;

task fulladder;
input A1;
input B1;
input C4;
output reg Sum1;
output reg C0;
begin

        Sum1=0;
        C0=0;
      {C0,Sum1}=A1+B1+C4;
end 
endtask


task automatic ripple;
input [bits:0] A2;
input [bits:0] B2;
input C1;
output reg [bits:0]sum2;
output reg cout;
reg [bits:0]sum3,sum4;

reg [bits+1:0] C,C3;
begin

            sum2=0;
            sum3=0;
            sum4=0;
           cout=0;
            C=0;
            C3=0;

            C[0]=0;        
            C3[0]=1;
            for (k=0;k<=bits;k=k+1)
            begin 
                 fulladder(A2[k],B2[k],C[k],sum3[k],C[k+1]);
                 fulladder(A2[k],B2[k],C3[k],sum4[k],C3[k+1]);

            end
            if(C1==0)
            begin
                cout=C[bits+1];
                sum2=sum3;
            end
            else if(C1==1)
            begin
                cout=C3[bits+1];
                sum2=sum4;
            end

end
endtask


always@(rst_n or A or B or Cin)
begin
    if(!rst_n)
     begin
            Sum=0;
            Cout=0;
            C2=0;
     end


         C2[0]=Cin;
         for (k=0;k<=width;k=k+bits+1)
         begin
              ripple(A[k+:bits],B[k+:bits],C2[k],Sum[k+:bits],C2[k+bits+1]);

         end
         Cout=C2[width+1];


end


endmodule

in this specifically, A,B 's values are not copying in the A2,B2 variables in the ripple task.

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The issue could be stemming from the fact that you don't have any delays in the verilog code under the for loop (including the code included in the tasks). There could be multiple driver issue.

You can try adding #1 in your for loop and see if that helps.

I notice that the question is pretty old. Might be useful for future exchangers.

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