My code for the design block and the testbench compiles; however, when I simulate, I'm not getting the correct output. Can anyone tell me where I'm going wrong in my code?
Here is the code for testbench:
module testbench;
reg [511:0]FROM_LS;
reg CLK;
reg [63:0]TO_IF_ID;
initial
begin
CLK= 0;
TO_IF_ID[63:0]=63'b0;
FROM_LS[511:480]= 32'b00011_00000_00100_01100_11100_10111_01;
FROM_LS[479:448]=32'b00_11000_00100_01111_11111_00011_10000;
end
always
begin
#10 CLK= ~ CLK;
//FROM_LS[511:448]= ~ FROM_LS[511:448];
$display("FROM_LS= %b", FROM_LS);
$display("TO_IF_ID= %b", TO_IF_ID);
end
endmodule
and here is the code for the design block:
module inst_line_buffer(input wire [511:0]from_LS,
input wire clk,
output reg [63:0]to_if_id);
parameter mem_size=16;
integer k;
reg [31:0] ilb[0:mem_size-1];
initial
begin
for (k = 0; k < mem_size ; k = k + 1)
begin
ilb[k] = 32'b00;
//$display ("ilb= %b",ilb[k]);
end
end
always #(posedge clk)
begin
ilb[0]= from_LS[511:480];
ilb[1]= from_LS[479:448];
ilb[2]= from_LS[447:416];
ilb[3]= from_LS[415:384];
ilb[4]= from_LS[383:352];
ilb[5]= from_LS[351:320];
ilb[6]= from_LS[319:288];
ilb[7]= from_LS[287:256];
ilb[8]= from_LS[255:224];
ilb[9]= from_LS[223:192];
ilb[10]= from_LS[191:160];
ilb[11]= from_LS[159:128];
ilb[12]= from_LS[127:96];
ilb[13]= from_LS[95:64];
ilb[14]= from_LS[63:32];
ilb[15]= from_LS[31:00];
to_if_id [63:32]= ilb[0];
to_if_id [31:0]= ilb[1];
$display("ilb= %b", ilb[1]);
end
endmodule
I'm expecting that the value of TO_IF_ID should be 0001100000001000110011100101110100110000010001111111110001110000, but I'm getting all zeros.
When you run a simulation on your testbench module, TO_IF_ID is always 0 because you only assigned a value to it once at time 0 in your initial block. If you want the value to change, it needs to be driven somehow.
As Andy pointed out in a comment, you probably meant to instantiate the inst_line_buffer module in your testbench. Verilog will not do this magically for you. But then, you should declare TO_IF_ID as a wire instead of a reg and remove it from the initial block.
module testbench;
reg [511:0]FROM_LS;
reg CLK;
wire [63:0]TO_IF_ID;
inst_line_buffer inst_line_buffer (
.from_LS (FROM_LS),
.clk (CLK),
.to_if_id (TO_IF_ID)
);
initial begin
CLK= 0;
FROM_LS[511:480]= 32'b00011_00000_00100_01100_11100_10111_01;
FROM_LS[479:448]=32'b00_11000_00100_01111_11111_00011_10000;
#500 $finish;
end
always
begin
#10 CLK= ~ CLK;
//FROM_LS[511:448]= ~ FROM_LS[511:448];
$display("FROM_LS= %b", FROM_LS);
$display("TO_IF_ID= %b", TO_IF_ID);
end
endmodule
Related
I am trying to delay a 32-bit signal using shift register. My logic is a single flip flop delay a signal by 1 clk so I use shift register as it is combination of flip flop can someone guide me what is wrong with this code.
module delay_n_cycles (
input wire [31:0] data_in,
input wire clk,
output reg [31:0] data_out,
parameter N = 5
);
reg [31:0] shift_reg;
always #(posedge clk) begin
shift_reg <= {shift_reg[30:0], data_in};
if (N == 0) begin
data_out <= shift_reg[31];
end else begin
data_out <= shift_reg[N-1];
end
end
endmodule
First of all, your code is syntactically wrong. parameter cannot be declared in a way you provided.
Your shift register is only 32 bit wide. Usually, to delay multi-bit data this way, you need to keep N copies of data in the register, shift them at one end and read at the other. I guess the following should help:
module delay_n_cycles #(parameter N = 5)(
input wire [31:0] data_in,
input wire clk,
output reg [31:0] data_out
);
reg [N-1:0][31:0] shift_reg;
always #(posedge clk) begin
shift_reg <= (shift_reg << 32) | data_in;
data_out <= shift_reg[N-1];
end
endmodule
This code will work with system verilog because it used packed multi-dimensional arrays.
You need to shift the reg by 32 (width of the data) in packed version.
Here is an example of a testbench:
module tb();
bit clk;
int clkCount;
initial
forever begin
#5 clk = ~clk;
clkCount++;
end
logic [31:0] data_in, data_out;
initial begin
$monitor("%0t (%0d) [%h]: %0d --> %0d", $time, clkCount, ds.shift_reg[4], data_in, ds.data_out);
for(int i = 0; i < 20; i++) begin
#10 data_in = i;
end
$finish;
end
delay_n_cycles ds(data_in, clk, data_out);
endmodule
I wrote this Verilog code. The inner module is an 8-bit mux, and the top module is used to test the mux. It should display 11110000, but it displayed xxxxxxxx every time. How do I fix this?
module testbench;
reg CLK;
test mytest(CLK);
initial begin
CLK = 1'b0;
#10
CLK = 1'b1;
end
endmodule
module test(CLK);
input CLK;
reg [7:0] in0,in1;
reg sel;
wire [7:0] out;
mux myux(in0,in1,sel,out);
always #(posedge CLK) begin
sel = 1'b0;
in0 = 8'b11110000;
$display("%b",out);
end
endmodule
This is the mux module:
module mux(in0,in1,sel,out);
input sel;
input [7:0] in1,in0;
output [7:0] out;
reg out;
always #(in0,in1,sel) begin
if(sel == 1'b0) begin
out = in0;
end
else begin
out = in1;
end
end
endmodule
The problem is that you did not run your simulation long enough. You only ran it for one clock cycle. Here is one way to change your testbench module to run many clock cycles:
module testbench;
reg CLK;
test mytest(CLK);
initial begin
CLK = 1'b0;
forever #10 CLK =~CLK;
end
initial #1000 $finish;
endmodule
I now see output like this:
xxxxxxxx
11110000
11110000
11110000
11110000
Also, I got a compile error with your code. In your mux module, you should change:
reg out;
to:
reg [7:0] out;
This my Verilog code to convert the number x into form x=a0*R+a1 ,e.g 51 = 5*10 +1. My code does not work, it cannot enter the always loop.
`timescale 1ns / 1ps
module poly(
input [15:0] r,
input [15:0] x,
output reg[15:0] a1,
output reg [15:0] a0,
output finish,
input clk,
input reset
);
reg [15:0] sum;
assign finish =(sum > x);
always# (posedge clk )
begin
if(reset)
begin
a0 <=0;
sum <=0;
end
else if (!finish)
begin
a0 <=a0+1;
sum <= sum+r;
end
else
a1<=x-sum;
end
initial begin
$monitor ( "a1=%b,a0=%b,finish=%b,reset=%b",a1,a0,finish,reset);
end
endmodule
testbench
`timescale 1ns / 1ps
module tb_p;
reg [15:0] r;
reg [15:0] x;
wire[15:0] a1;
wire [15:0] a0;
wire finish;
reg clk;
reg reset;
initial clk=0;
always #5 clk=!clk;
poly m1(r,x,a1,a0,finish,clk,reset);
initial begin
r<=10;
x <=17;
#1 reset<=1;
#2 reset<=0;
end
endmodule
Since your reset signal is synchronous to the clock, you need to extend it so that it is high for at least one posedge of the clock:
initial begin
r<=10;
x <=17;
#1 reset<=1;
#20 reset<=0;
#500 $finish;
end
Note that I added $finish just so my simulation would end.
I want to infer a simple flip flop using verilog. Here is the code.
module tb_simpleRegister();
reg clk;
reg a;
wire b;
simpleRegister dut
(
.clk(clk),
.a(a),
.b(b),
.c(c)
);
initial begin
clk=1;
a=0;
#10
a=1;
#10
a=0;
end
always #5 clk = ~clk;
endmodule
module simpleRegister(
input clk,
input a,
output reg b,
output reg c
);
always #(posedge clk) begin
b <= a;
c <= b;
end
endmodule
And here is the result when I run it. The b output of dut does not behave like a flip flop. However output c does. Any comments on why is this happening?
I would rewrite the test bench as follows:
initial begin
#(posedge clk);
a<=0;
#(posedge clk);
a<=1;
#(posedge clk);
a<=0;
end
//Clock in separate process
initial begin
clk=1;
forever begin
#5 clk = ~clk;
end
end
The non-blocking assignment will ensure the value of a is changed just after the clock edge giving the testbench a full cycle setup.
I have tried connecting a module output to a register, as follows:
module test
(
input rst_n,
input clk,
output reg [7:0] count
);
always #(posedge clk or negedge rst_n) begin
if(!rst_n) begin
count <= 7'h0;
end else begin
if(count == 8) begin
count <= count;
end else begin
count <= count + 1'b1;
end
end
end
endmodule
module test_tb;
reg clk;
reg rst_n;
reg [7:0] counter;
initial begin
clk = 1'b0;
rst_n = 1'b0;
# 10;
rst_n = 1'b1;
end
always begin
#20 clk <= ~clk;
end
test test1 (
.rst_n(rst_n),
.clk(clk),
.count(counter) /* This is the problematic line! */
);
endmodule
I got the error "Illegal output or inout port connection for "port 'count'" in ModelSim. Even though the error matches my code, I do not understand why, fundamentally, I cannot connect a module output to a register.
Why can I not connect a module output to a register in Verilog?
You can only assign a value to a reg within a procedural always block. You can not drive a reg from a module instance. That would be a continuous assisgnment.
Use a wire inside test_tb.