Problem: I'm trying to manipulate 16 bit binary numbers in Verilog. The results I'm getting do not seem to match the expected results. I've isolated the problem in that the testbench.v seems to be sending the wrong values to my classify.v file.
This is what my testbench.v file looks like.
module testbench3();
reg clk, reset; // clock and reset are internal
reg [0:15] data_row;
wire [0:1] actual_class;
reg EN;
reg [0:15] memory [0:2]; //HERE
integer i;
classify dut(.actual_class(actual_class), .data_row(data_row), .EN(EN));
// Set up the system clk
always begin
#5 clk <= !clk;
end
initial begin // ASSIGN 16 bit to memory
memory[0] <= 0001111111000000;
memory[1] <= 0010111111000000;
memory[2] <= 0010111111000000;
end
initial begin
clk <= 0;
EN <= 0;
i <= 0;
reset <= 0;
#27;
reset <= 1;
end
always #(posedge clk) begin
data_row <= memory[i];
i <= i + 1;
$display ("%b", data_row); // HERE
if(i == 3) begin
$display("End simulation");
$finish;
end
EN = 1;
end
endmodule
I'm expecting the console to display:
0001111111000000
0010111111000000
0010111111000000
and what I'm getting are these values instead:
0101111111000000
1110111111000000
1110111111000000
Not sure where these values are coming from.
I'm using Icarus Verilog 0.10.0, if that helps.
When you initialize your memory your are using decimal values, not binary.
Add 16'b to the front:
memory[0] <= 16'b0001111111000000;
memory[1] <= 16'b0010111111000000;
memory[2] <= 16'b0010111111000000;
Related
well, I have this code, that is working perfectly:
module syncRX(clk, signal, detect);
input clk, signal;
output reg [7:0] detect = 0;
reg [7:0] delay = 0;
//wire clk_1khz;
freq_div div(.clk(clk), .clk_1khz(clk_1khz));
always #(posedge signal)
begin
detect <= detect + 1;
delay <= 0;
end
always #(posedge clk_1khz)
begin
delay <= delay + 1;
end
endmodule // top
module freq_div(input clk, output reg clk_1khz);
reg [12:0] count = 0;
always #(posedge clk)
begin
if(count == 6000)
begin
clk_1khz <= ~clk_1khz;
count <= 0;
end
else
count <= count + 1;
end
endmodule
The problem appears when I change the line "detect <= detect + 1;" to "detect <= delay;".
The intention is calculate the period of the signal, but I get this warning message of Icestorm:
Warning: No clocks found in design
And the FPGA stop working...
Please, anyone have an idea what is going bad?
Thanks to all!
By the votes of the question I could see that is not good one, maybe because community consider it that there is already documented, but I still can not find solution to the problem, I did some improvements and I will try again to find help here, I have this code now, that syntethize perfectly:
module syncRX(clk, signal, detect);
input clk, signal;
output [7:0] detect;
reg [7:0] detect_aux = 8'b0;
reg rst;
assign detect = detect_aux & ~rst;
freq_div div(.clk(clk), .clk_1khz(clk_1khz));
always #(posedge signal)
rst <= 1;
always #(posedge clk_1khz)
detect_aux <= detect_aux + 1;
endmodule // top
module freq_div(input clk, output reg clk_1khz);
reg [12:0] count = 0;
always #(posedge clk)
begin
if(count == 6000)
begin
clk_1khz <= ~clk_1khz;
count <= 0;
end
else
count <= count + 1;
end
endmodule
The problem is that
reg rst;
assign detect = detect_aux & ~rst;
Seams do nothingh. Any suggestion?
Thanks
The problem is that delay is multiply driven (driving from multiple always blocks is not allowed in synthesis) which is undefined behaviour (in this case I believe the constant '0' will be used). It should also be at least a warning.
Sorry if anything in here seems obvious but I am starting out in this new FPGA thing and I really enjoy it so far but this is driving me crazy.
Here is the Verilog code for a block that should in principle do the following to an 8 bit register:
00000001
00000010
00000100
.....
01000000
10000000
01000000
00100000
module bit_bouncer(clock, enable, bouncer_out);
//INPUTS PORTS
input clock;
input enable;
//OUTPUTS PORTS
output bouncer_out;
//INPUT DATA TYPE
wire clock;
wire enable;
//OUTPUT DATA TYPE
reg [7:0] bouncer_out = 8'b00000001;
//Register to store data
reg direction = 0;
//CODE STARTS HERE
always # (posedge clock) begin
if(enable) begin
bouncer_out = direction ? (bouncer_out >> 1) : (bouncer_out << 1);
direction <= (bouncer_out == 8'b00000001 || bouncer_out == 8'b10000000) ? ~direction : direction;
end
end
endmodule
This works perfectly in simulation but fails on the FPGA (DE10-Nano board, if interested).
I should also point out that this gets driven by a clock passed trough a PLL on the FPGA that is then
passed trough a divideByN block.
Here is the code for the divideByN block:
module clk_divn #(
parameter WIDTH = 20,
parameter N = 1000000)
(clk,reset, clk_out);
input clk;
input reset;
output clk_out;
reg [WIDTH-1:0] pos_count = {WIDTH{1'b0}};
reg [WIDTH-1:0] neg_count = {WIDTH{1'b0}};
wire [WIDTH-1:0] r_nxt = {WIDTH{1'b0}};
always #(posedge clk)
if (reset)
pos_count <=0;
else if (pos_count ==N-1) pos_count <= 0;
else pos_count<= pos_count +1;
always #(negedge clk)
if (reset)
neg_count <=0;
else if (neg_count ==N-1) neg_count <= 0;
else neg_count<= neg_count +1;
assign clk_out = ((pos_count > (N>>1)) | (neg_count > (N>>1)));
endmodule
The divideByN has also been tested in simulation and works fine.
I actually made a simulation in which the divideByN is connected to the "bouncer_block" if I can
call it like that and it also works.
Everything simulates but nothing works in real life....but isn't it always like that :P
I hope someone can help me figure this out because I really want to learn more about FPGA and use
them in future projects.
If you read all this you are awesome and I wish you an amazing day :)
Your bit bouncer is not operating synchronously to the system clock and neither does it have a reset condition, which is a recipe for trouble.
A better approach is to use a clock strobe and test for it on edges of the main system clock. Also, all inputs from tactile buttons should be synchronised to the system clock and debounced. Something like this:
Schematic
RTL
BitBouncer
module BitBouncer
(
input wire clock,
input wire reset,
input wire enable,
input wire clock_strobe,
output reg[7:0] bouncer_out
);
// Register to store data
reg direction = 0;
// CODE STARTS HERE
always #(posedge clock)
begin
if (reset)
begin
bouncer_out = 1;
direction = 0;
end
else if (enable && clock_strobe)
begin
bouncer_out = direction ? (bouncer_out >> 1) : (bouncer_out << 1);
direction <= (bouncer_out == 8'b00000001 || bouncer_out == 8'b10000000) ? ~direction : direction;
end
end
endmodule
ClockStrobe
module ClockStrobe
#(
parameter MAX_COUNT = 50000000
)
(
input wire clock,
input wire reset,
output reg clock_strobe
);
reg [$clog2(MAX_COUNT) - 1: 0] counter;
always #(posedge clock)
begin
if (reset)
begin
counter <= 0;
end
else
begin
counter <= counter + 1;
if (counter == MAX_COUNT)
begin
clock_strobe <= 1;
counter <= 0;
end
else
begin
clock_strobe <= 0;
end
end
end
endmodule
Sync
module Sync
(
input wire clock,
input wire in,
output reg out
);
reg [2:0] sync_buffer;
initial
begin
out = 0;
sync_buffer = 3'd0;
end
always #*
begin
out <= sync_buffer[2];
end
always #(posedge clock)
begin
sync_buffer[0] <= in;
sync_buffer[2:1] <= sync_buffer[1:0];
end
endmodule
Debounce
module Debounce
#(
parameter MAX_COUNT = 2500000
)
(
input wire clock,
input wire in,
output reg out
);
reg previous_in;
reg [$clog2(MAX_COUNT) - 1:0] counter;
initial begin
previous_in = 0;
counter = 0;
out = 0;
end
always #(posedge clock)
begin
counter <= counter + 1;
if (counter == MAX_COUNT)
begin
out <= previous_in;
counter <= 0;
end
else if (in != previous_in)
begin
counter <= 0;
end
previous_in <= in;
end
endmodule
I have tried to add a reset with no success but I have made my own divideByN and kept the reset Charles suggested and now it's working flawlessly. I think the code for the divideByN I took online might be unable to synthesize properly. Here is my new code for the divideByN:
module my_div_n #(parameter N = 1_000_000, parameter WIDTH = 20) (clock_in,
clock_out);
input wire clock_in;
output reg clock_out;
reg[WIDTH-2:0] counter; //WIDTH-2 because the last bit is taken care of by the fact that we flip the output (it acts as the last bit)
always # (posedge clock_in) begin
counter <= counter + 19'b1;
if(counter == N>>1) begin
counter <= 0;
clock_out <= !clock_out;
end
end
endmodule
And the code for my bit_bouncer:
module bit_bouncer(clock, enable, reset, bouncer_out);
//INPUTS PORTS
input clock;
input enable;
input reset;
//OUTPUTS PORTS
output [7:0] bouncer_out;
//INPUT DATA TYPE
wire clock;
wire enable;
wire reset;
//OUTPUT DATA TYPE
reg [7:0] bouncer_out;
//Register to store data
reg direction;
//CODE STARTS HERE
always # (posedge clock) begin
if(reset) begin
bouncer_out <= 8'b00000001;
direction <= 0;
end
else if(enable) begin
bouncer_out = direction ? (bouncer_out >> 1) : (bouncer_out << 1);
direction <= (bouncer_out == 8'b00000001 || bouncer_out == 8'b10000000) ? ~direction : direction;
end
end
endmodule
Here how everything is wired:
I would still like to know the purpose of the clock strobe because you make it seem as if I should probably know this if I want to understand my circuit better and all about synchronicity.
I wanted to design a FIFO having a certain depth and width. The Verilog code of the FIFO is written in Vivado 2017.4. The code is able to to read the input data, but it is only showing XX as the output. The design sources and test bench of the FIFO is given below. Help me to find the problem.
module fifo #(parameter WIDTH=8, parameter DEPTH=8) (
input wire [WIDTH-1:0] data_in,
output reg [WIDTH-1:0] data_out,
output reg data_valid,
input wire reset,
input wire clk
);
function integer clog2(input reg [32-1:0] value);
begin
value = value-1;
for (clog2=0; value>0; clog2=clog2+1)
value = value>>1;
end
endfunction
reg [WIDTH-1:0] data [DEPTH-1:0];
reg [clog2(DEPTH)-1:0] write_pointer;
reg [clog2(DEPTH)-1:0] read_pointer;
always #(posedge clk) begin
if (reset == 1'b0) begin
write_pointer <= 0;
read_pointer <= 1;
data_valid <= 0;
end else begin
if (write_pointer == DEPTH-1) write_pointer <= 0;
else write_pointer <= write_pointer + 1;
if (read_pointer == DEPTH-1) read_pointer <= 0;
else read_pointer <= read_pointer + 1;
data[write_pointer] <= data_in;
data_out <= data[read_pointer];
end
if (read_pointer == 0) data_valid <= 1'b1;
end
endmodule
test bench
`timescale 1ns / 1ps
module fifo_tb;
parameter WIDTH = 16;
parameter DEPTH = 8;
reg reset;
reg clk;
reg [(WIDTH-1):0] data_in;
wire [(WIDTH-1):0] data_out;
wire data_valid;
fifo #(WIDTH,DEPTH) U0(data_in,data_out,data_valid,reset,clk);
initial begin
clk = 0;
reset = 1;
#1 reset = 0;
#1 reset = 1;
end
// Create clock
always
#5 clk = ~clk;
reg signed [15:0] rom_memory [4096-1:0];
integer i=0;
initial
begin
$readmemh("C:\\Users\\input_7_zz.txt",rom_memory);
end
always#(posedge clk )
begin
if(~reset)
begin
data_in <= 0;
end
else
begin
data_in <= rom_memory[i];
i <= i+ 1;
end
end
endmodule
In your test bench code the clock is changed every 5 ticks:
// Create clock
always
#5 clk = ~clk;
The reset in RTL uses posedge of this clock:
always #(posedge clk) begin
if (reset == 1'b0) begin
write_pointer <= 0;
read_pointer <= 1;
data_valid <= 0;
So, the reset action could happen only if the posedge clk could be detected during the reset period. In other words you have a synchronous reset.
Nevertheless, in your test bench code your reset lasts only a single tick:
initial begin
clk = 0;
reset = 1;
#1 reset = 0;
#1 reset = 1; // << one tick after the reset was asserted.
end
Potentially you have 2 possible solutions.
1) keep the synchronous reset, but make sure that the posedge of the clk could be detected during the reset. So, make it bigger than a clock cycle (or at least half clock cycle if you are sure when it comes). Something like 5 should work in your case. Make it 10 or more to be sure for arbitrary starting points.
initial begin
clk = 0;
reset = 1;
#1 reset = 0;
#5 reset = 1; // << 5 tick after the reset was asserted.
The reset above will last from time 1 to time 6. The first posegde will happen at time 5. So, it should be sufficient in your case.
2) you can use an asynchronous reset in RTL which will look as the following:
always #(posedge clk or reset) begin
if (reset == 1'b0) begin
write_pointer <= 0;
read_pointer <= 1;
data_valid <= 0;
In the above case the always block will be executed whenever 'reset' changes. However you have to be careful about the timing of other assignment there. They could happen when you deassert reset with some offset from the posedge clk.
This is code for ALU that does addition and multiplication only. An addition is handled in same clock cycle but the multiplication result has to be delayed by 3 clock cycles.
module my_addmul(
//control signals
input i_clk,
input i_rst,
input i_en,
//add=01, mul=10
input [1:0] i_op,
//input and output registers
input [31:0] i_A,
input [31:0] i_B,
output [31:0] o_D,
//to signal if output is valid
output o_done
);
//registers to save output
reg [31:0] r_D;
reg [63:0] r_mul;//(*keep="true"*)
reg r_mul_done;
reg r_mul_done2;
reg r_done;
//updating outputs
assign o_D = r_D;
assign o_done = r_done;
always # (posedge i_clk)
begin
r_done <= 0;
r_mul_done <= 0;
if (i_rst) begin
r_D <= 0;
r_mul <= 0;
r_mul_done <= 0;
r_mul_done2 <= 0;
end else if (i_clk == 1) begin
if (i_en == 1) begin
//addition - assignment directly to OP registers
if (i_op == 01) begin
r_done <= 1;
r_D <= i_A + i_B;
//multiplication - indirect assignment to OP registers
end else if (i_op == 2'b10) begin
r_mul <= i_A * i_B;
r_mul_done <= 1;
end
end
//1-clock cycle delay
r_mul_done2 <= (r_mul_done == 1) ? 1 : 0;
//updating outputs in the 3rd cycle
if (r_mul_done2 == 1) begin
r_D <= r_mul[31:0];
r_done <= 1;
end
end
end
endmodule
The problem is that if the keep attribute is not used, the r_mul register that stores the multiplication output until 3rd clock cycle is optimised out. I read on the problem and realised that Vivado is thinking like this: "If the multiplication happens every clock cycle, the r_mul is over-written before it is sent to output. Therefore, it is a register being written but not read, Lets remove it!" Since I insert the 3 clock cycle wait in test bench, the simulation result is always accurate. I want to know what is the "Proper" way of doing this so I don't have to use the keep attribute. It is an ok solution but I think useful techniques should be learned so hacks don't have to be used. Any ideas or discussion welcome.
If I want to delay a signal, I'd probably insert flops for that. You can probably flop your mul_output like the way you do for the mul_done signal. Also, it is better to have different always blocks for doing the same. You can check the code below but it might be buggy since I haven't simulated/synthesized it -
module my_addmul(
//control signals
input i_clk,
input i_rst,
input i_en,
//add=01, mul=10
input [1:0] i_op,
//input and output registers
input [31:0] i_A,
input [31:0] i_B,
output [31:0] o_D,
//to signal if output is valid
output o_done
);
//registers to save output
reg [31:0] r_D;
reg [63:0] r_mul;//(*keep="true"*)
reg r_mul_1;
reg r_mul_2;
reg r_mul_done;
reg r_mul_done2;
reg r_done;
//updating outputs
assign o_D = r_D;
assign o_done = r_done;
always # (posedge i_clk)
begin
r_done <= 0;
r_mul_done <= 0;
if (i_rst) begin
r_D <= 0;
r_mul <= 0;
r_mul_done <= 0;
r_mul_done2 <= 0;
end else if (i_clk == 1) begin
if (i_en == 1) begin
//addition - assignment directly to OP registers
if (i_op == 01) begin
r_done <= 1;
r_D <= i_A + i_B;
//multiplication - indirect assignment to OP registers
end else if (i_op == 2'b10) begin
r_mul <= i_A * i_B;
r_mul_done <= 1;
end
end
end
end
always # (posedge i_clk)
begin
if (i_rst)
begin
r_mul_1 <= 0;
r_mul_done2 <= 0;
end
else
begin
r_mul_1 <= r_mul;
r_mul_done2 <= r_mul_done;
end
end
always # (posedge i_clk)
begin
if (i_rst)
begin
r_D <= 0;
r_done <= 0;
end
else
begin
r_D <= r_mul_1;
r_done <= r_mul_done2;
end
end
endmodule
How do I initialize the array Save_state? This statement is giving X value at the output:
reg [9:0] count
reg [9:0] Save_state [0: 1024];
always # (posedge Clock )
Count <=count+1 ;
Save_state[count] <=count ;
You can use an initial block as well. This is allowed in simulation and is synthesizable on some architectures (Xilinx FPGA and CPLD support register initialization)
reg [9:0] count
reg [9:0] Save_state [0: 1024];
integer i;
initial begin
count = 0;
for (i=0;i<=1024;i=i+1)
Save_state[i] = 0;
end
always # (posedge Clock ) begin
count <= count + 1;
Save_state[count] <= count;
end
Although for this particular example, in which the elements of the Save_state array will always have the same value, you can do like this (synthesizable on Xilinx and Altera, AFAIK):
reg [9:0] Save_state [0: 1024];
integer i;
initial begin
for (i=0;i<=1024;i=i+1)
Save_state[i] = i[9:0];
end
And at the beginning of you simulation, Save_state already have the values 0,1,2,...,1023 stored in it.
You can use a reset port to initialize count and save_state such as the following code :
integer i;
reg [9:0] count;
reg [9:0] save_state [0:1024];
always #(posedge clock or posedge reset) begin
if (reset) begin
count <= 0;
for (i=0; i<=1024; i=i+1)
save_state[i] <= 0;
end
else begin
count <= count + 1;
save_state[count] <= count;
end
end
The two statements inside the else block is applied at the same time and at the end of always block.