Implementation of Network on Chip on FPGA

Question

I'm new to the verilog. I receive following warning when I synthesize my code on the Xilinx 14.3

Synthesizing Unit <Router_Debug> .

Related source file is "Router_Debug.v".

WARNING:Xst:646 - Signal <P0_data_out<16:23>> is assigned but never used. This unconnected signal will be trimmed during the optimization process.

Unit <Router_Debug> synthesized.

File: Router_Debug.v

module Router_Debug(output wire signed [0:31]out_N,
                    output wire signed [0:7]out_E,
                    output wire signed [0:7]out_W,
                    output wire signed [0:7]out_S,
                    output wire signed [0:7]out_L,
                    input wire signed [0:7]in_N,
                    input wire signed [0:7]in_E,
                    input wire signed [0:7]in_W,
                    input wire signed [0:7]in_S,
                    input wire signed [0:7]in_L,
                    input clk);

    wire signed [0:31]P0_data_out;
    reg signed [0:31]P0_data_in; 

    wire signed [0:31]P1_data_out;
    reg signed [0:31]P1_data_in;

    wire signed[0:31]P2_data_out;
    reg signed[0:31]P2_data_in;

    wire signed[0:31]P3_data_out;
    reg signed[0:31]P3_data_in;

    wire signed[0:31]P4_data_out;
    reg signed[0:31]P4_data_in;

always @ (*)
begin

    P0_data_in[0:7]<=P1_data_out[0:7];
    P0_data_in[8:15]<=P2_data_out[0:7];
    P0_data_in[16:23]<=P3_data_out[0:7];
    P0_data_in[24:31]<=P4_data_out[0:7];

    P1_data_in[0:7]<=P0_data_out[0:7];
    P1_data_in[8:15]<=P2_data_out[8:15];
    P1_data_in[16:23]<=P3_data_out[8:15];
    P1_data_in[24:31]<=P4_data_out[8:15];

    P2_data_in[0:7]<=P0_data_out[8:15];
    P2_data_in[8:15]<=P1_data_out[8:15];
    P2_data_in[16:23]<=P3_data_out[16:23];
    P2_data_in[24:31]<=P4_data_out[16:23];

    P3_data_in[0:31]<=P0_data_out[16:23];
    P3_data_in[8:15]<=P1_data_out[16:23];
    P3_data_in[16:23]<=P2_data_out[16:23];
    P3_data_in[24:31]<=P4_data_out[24:31];

    P4_data_in[0:7]<=P0_data_out[24:31];
    P4_data_in[8:15]<=P1_data_out[24:31];
    P4_data_in[16:23]<=P2_data_out[24:31];
    P4_data_in[24:31]<=P3_data_out[24:31];

end

    Port_Debug P0(P0_data_out,P0_data_in,in_N,out_N,clk,3'd0);//mesh_size,3'd0);
    Port_Debug P1(P1_data_out,P1_data_in,in_W,out_W,clk,3'd1);//mesh_size,3'd1);
    Port_Debug P2(P2_data_out,P2_data_in,in_S,out_S,clk,3'd2);//mesh_size,3'd2);
    Port_Debug P3(P3_data_out,P3_data_in,in_L,out_L,clk,3'd3);//mesh_size,3'd3);
    Port_Debug P4(P4_data_out,P4_data_in,in_E,out_E,clk,3'd4);//mesh_size,3'd4) 

endmodule

I've searched on the google and found relevant problem's solutions but that didn't help me. So any help will be much appreciated. Thanks!

Answer 1

I can't do much with your code because:

• Your error message does not say which signal is optimised away
• I have no idea what Port_Debug does.

You have a code error in there:
You use non-blocking <= assignments in a combinatorial block. That should be blocking = .

You code style is unorthodox:

• All you signal indices are from low to high: customary is from high to low. Just like in computer numbers the bits are from MS (left) to LS (right) .I have no idea if signed [0:7] even works...
• Don't make very long lines. Your ports are not readable. This is readable:
  output wire signed [0:31]out_N,
output wire signed [0:7]out_E,
output wire signed [0:7]out_W,
output wire signed [0:7]out_S,
...
  (I have seen this before and always in the ports. I start to think it is some sort of bad emacs macro.)
• When connecting signals always use by reference:
  Port_Debug(.portname0(P0_data_out),
.portname1(P0_data_in),
...

...............

There is an anomaly in your code:
P3_data_in[0:31]<=P0_data_out[16:23];
Does not match the pattern. You probably wanted: P3_data_in[0:7]<=P0_data_out[16:23];