Verilog-The FF/Latch will be trimmed during the optimization process

[aswathymohan]

I am using Xilinx ISE Project navigator (P.28d) for writing the verilog code for vending machine. Whats wrong with my code? So many warnings, but no errors.Pl help..it too urgent

module vend(
    input clk,
    input reset,
    input cancel,
    input sel1,
    input sel2,
    inout [6:0] money,
    input Rs_10,
    input Rs_20,
    output reg product,
    output reg [6:0] change,
    output reg [6:0] returns
    ); 
     wire wait_1,wait_2;
     reg st_1,st_2,st_3,st_4;
     wire pr_1,pr_2;
     reg nx_1,nx_2;
     reg snacks,coffee;
     reg snack_c,coffee_c;
     reg [6:0] money_count;

always @(posedge clk)

begin   : count
if (sel1==1)
    begin
    if(pr_1==1)
          begin
    nx_1<=wait_1;

          if((Rs_10) & ~(Rs_20))
    begin
    nx_1<=st_1;
    money_count=(money_count+7'b0001010);
          if(money_count>=7'b0011110)
    begin
                                    nx_1<=snacks;
    change<=({0,money_count}-7'b0011110);
                                    snack_c<=snack_c-1;
    disable count;
    end
    nx_1<=wait_1;
    if(cancel==1)
    begin
    returns<=({0,money_count});
    disable count;
    end

    end
    if(~(Rs_10) &(Rs_20))
    begin

    nx_1<=st_2;
    money_count=(money_count+7'b0010100);
    if(money_count>=7'b0011110)
    begin
                                    nx_1<=snacks;
    change<=({0,money_count}-7'b0011110);
                                    snack_c<=snack_c-1;
    disable count;
          end
                                    nx_1<=wait_1;
    if(cancel==1)
    begin
          returns<=({0,money_count});
    disable count;
    end
    end

    end
    end 
    else
            begin
                snack_c<=1'd4;
                nx_1<=reset;
                product<=0;
            end


          if (sel2==1)
    begin
    if(pr_2==1)
    begin
    nx_2<=wait_2;

    if((Rs_10) & ~(Rs_20))
    begin
    nx_2<=st_3;
    money_count=(money_count+7'b0001010);
    if(money_count>=7'b0101000)
    begin
    nx_2<=coffee;
    change<=({0,money_count}-7'b0101000);
    coffee_c<=coffee_c-1;
    disable count;
    end
    nx_2<=wait_2;
    if(cancel==1)
    begin
    returns<={0,money_count};
    disable count;

    end

    end
          if(~(Rs_10) &(Rs_20))
    begin

    nx_2<=st_4;
                                money_count=money_count+7'b0010100;
    if(money_count>=7'b0101000)
    begin
    nx_2<=coffee;
    change<=({0,money_count}-7'b0101000);
    coffee_c<=coffee_c-1;
    disable count;
    end
    nx_2<=wait_2;
    if(cancel==1)
    begin
    returns<=({0,money_count});
    disable count;

    end
    end

    end
    end 
        else
            begin
                coffee_c<=1'd4;
                nx_2<=reset;
                product<=0;
            end

end 
endmodule
                                  nx_1<=snacks;
    change<=({0,money_count}-7'b0011110);
                                    snack_c<=snack_c-1;
    disable count;
    end
    nx_1<=wait_1;
    if(cancel==1)
    begin
    returns<=({0,money_count});
    disable count;
    end

    end
    if(~(Rs_10) &(Rs_20))
    begin

    nx_1<=st_2;
    money_count=(money_count+7'b0010100);
    if(money_count>=7'b0011110)
    begin
                                    nx_1<=snacks;
    change<=({0,money_count}-7'b0011110);
                                    snack_c<=snack_c-1;
    disable count;
          end
                                    nx_1<=wait_1;
    if(cancel==1)
    begin
          returns<=({0,money_count});
    disable count;
    end
    end

    end
    end 
    else
            begin
                snack_c<=1'd4;
                nx_1<=reset;
                product<=0;
            end


          if (sel2==1)
    begin
    if(pr_2==1)
    begin
    nx_2<=wait_2;

    if((Rs_10) & ~(Rs_20))
    begin
    nx_2<=st_3;
    money_count=(money_count+7'b0001010);
    if(money_count>=7'b0101000)
    begin
    nx_2<=coffee;
    change<=({0,money_count}-7'b0101000);
    coffee_c<=coffee_c-1;
    disable count;
    end
    nx_2<=wait_2;
    if(cancel==1)
    begin
    returns<={0,money_count};
    disable count;

    end

    end
          if(~(Rs_10) &(Rs_20))
    begin

    nx_2<=st_4;
                                money_count=money_count+7'b0010100;
    if(money_count>=7'b0101000)
    begin
    nx_2<=coffee;
    change<=({0,money_count}-7'b0101000);
    coffee_c<=coffee_c-1;
    disable count;
    end
    nx_2<=wait_2;
    if(cancel==1)
    begin
    returns<=({0,money_count});
    disable count;

    end
    end

    end
    end 
        else
            begin
                coffee_c<=1'd4;
                nx_2<=reset;
                product<=0;
            end

end 
endmodule

 Some of the warnings which i got
Xst:1710 - FF/Latch <returns_0> (without init value) has a constant value of 0 in block <vend>. This FF/Latch will be trimmed during the optimization process.
Xst:1710 - FF/Latch <change_0> (without init value) has a constant value of 0 in block <vend>. This FF/Latch will be trimmed during the optimization process.
Xst:2677 - Node <money_count_0> of sequential type is unconnected in block <vend>.

 

[std_match]

You never set the lowest bit of returns, change and money_count, so it has been optimized away.

 

[aswathymohan]

How to solve it??Since i am a beginner..I didnt understand what u mean

 

[std_match]

You don't have to fix it. The tool only informs you that it has replaced the logic for the lowest bit with a constant '0'.
If you think it is correct that the lowest bit is always '0', ignore these warnings.

 

[aswathymohan]

Thanks for ur response...ie the reason u mentioned ,why i was not getting simulation results.Pl help how to fix the pblm

 

[std_match]

You don't specify what problem you have now. The warnings you listed doesn't say that the design is wrong.
You should not debug by synthesizing into an FPGA. you should write a test bench and find the problems in simulation.

 

[aswathymohan]

I did the test bench,but the simulation was aborted ,giving a list of warnings.Then how to proceed??