In Verilog, I'm trying to use $readmemb to read .txt file but it only loads xxxxx (dont cares) on memory

Question

I need to load a memory with some data originally in binary. I read that $readmemb can be use for this, and there is even a method to make synthesizable.

So, I created another module named RAM_IN (which is not the testbench module) and "connected" to the top module.

Before knowing about $readmemb, I was using this code:

initial
begin
in_ram [0] <= 32'b11111111_000000000000000000000000; 
in_ram [1] <= 32'b10010111_000000000000000000000000;
in_ram [2] <= 32'b00110110_000000000000000000000000;
in_ram [3] <= 32'b00111110_000000000000000000000000;
in_ram [4] <= 32'b00111111_000000000000000000000000;
in_ram [5] <= 32'b00111110_000000000000000000000000;
end

But its too tiring for me to write 100 numbers like this, so implemented $readmemb like this:

module RAM_IN (pix_val, indx);


input [0:5] indx;
output [31:0] pix_val;


reg [31:0] pix_val;
reg [31:0] in_ram [0:4];

always @ (indx)
pix_val = in_ram [indx];

initial
begin
$readmemb("in_ram.txt", in_ram);
end

The purpose of reading this file, is to initially load 100 binary values (wich simulate the pixel intensity of a 10x10 image) one by one into the top module (which is going to process and spit a result later...)

I created a .txt file which looks content exactly like this

11111111000000000000000000000000
10010111000000000000000000000000
00110110000000000000000000000000
00111110000000000000000000000000
00111111000000000000000000000000

When I simulate, modelsim show me memory filled with xxxxxxxxxxxxxxxxx (dont care), it looks like isn't loading anything to the memory.

I don't know what I'm doing wrong. Likely isnt the dispossition of the numbers in the .txt file. Maybe is because I'm intending to load file with $readmemb in another module which is not testbench?

PD: The simulation of this process of filling the memory I'm doing only for practical purpose, the final intention is to put the Top module design into a full SoC which I think I will do using QSYS. But I'm very new at this so I'm still studying. Any help will be much appreciated!!!

It looks alright to me and it works alright, too. [http://www.edaplayground.com/x/5kxx](http://www.edaplayground.com/x/5kxx) — Matthew Taylor, May 10 '16 at 11:41
@hexafraction I would have said numbering a memory like this is pretty conventional: `reg [31:0] in_ram [0:4];`. — Matthew Taylor, May 10 '16 at 11:41

score 4 · Answer 1 · answered May 10 '16 at 13:02

Are you sure you run simulation?

Your code with TB:

module RAM_IN (pix_val, indx);

input [0:5] indx;
output [31:0] pix_val;

reg [31:0] pix_val;
reg [31:0] in_ram [0:4];

always @ (indx)
  pix_val = in_ram [indx];

initial
begin
  $readmemb("in_ram.txt", in_ram);
end

endmodule

module tb;
reg [0:5] indx; 
wire [31:0] pix_val;

RAM_IN ram_in(pix_val, indx);

initial
begin
  indx = 'b0;
  $monitor ($realtime, " Read Data = %0b" ,pix_val);
  repeat(4)
  begin
    #10;
    indx = indx + 1'd1;
  end
  $finish;
end
endmodule

With same in_ram.txt.

Questasim:

QuestaSim-64 qverilog 10.4 Compiler 2014.12 Dec  2 2014
Start time: 18:27:01 on May 10,2016
qverilog me.v 
-- Compiling module RAM_IN
-- Compiling module tb

Top level modules:
    tb
Reading pref.tcl

# 10.4

# vsim -lib work tb -c -do "run -all; quit -f" -appendlog -l qverilog.log -vopt 
# ** Note: (vsim-3812) Design is being optimized...
# //  Questa Sim-64
# //  Version 10.4 linux_x86_64 Dec  2 2014
# //
# //  Copyright 1991-2014 Mentor Graphics Corporation
# //  All Rights Reserved.
# //
# //  THIS WORK CONTAINS TRADE SECRET AND PROPRIETARY INFORMATION
# //  WHICH IS THE PROPERTY OF MENTOR GRAPHICS CORPORATION OR ITS
# //  LICENSORS AND IS SUBJECT TO LICENSE TERMS.
# //  THIS DOCUMENT CONTAINS TRADE SECRETS AND COMMERCIAL OR FINANCIAL
# //  INFORMATION THAT ARE PRIVILEGED, CONFIDENTIAL, AND EXEMPT FROM
# //  DISCLOSURE UNDER THE FREEDOM OF INFORMATION ACT, 5 U.S.C. SECTION 552.
# //  FURTHERMORE, THIS INFORMATION IS PROHIBITED FROM DISCLOSURE UNDER
# //  THE TRADE SECRETS ACT, 18 U.S.C. SECTION 1905.
# //
# Loading work.tb(fast)
# run -all
# 0 Read Data = 11111111000000000000000000000000
# 10 Read Data = 10010111000000000000000000000000
# 20 Read Data = 110110000000000000000000000000
# 30 Read Data = 111110000000000000000000000000
# ** Note: $finish    : me.v(34)
#    Time: 40 ns  Iteration: 0  Instance: /tb
# End time: 18:27:02 on May 10,2016, Elapsed time: 0:00:01
# Errors: 0, Warnings: 0

And Simulation:

friend, you are taking the $readmemb file as the top module and applying a test bench to it. The problem is that my $readmemb file is not the top module, it is controlled by the register "indx" and the test bench goes to the top module. For some reason, if I load one by one it works, but if use the $readmemb instruction it loads xxxxxxxxxxxxxxxx. Do you think if I post the whole code, can give me a hand on this? Thanks — sujeto1, May 16 '16 at 07:06

score 2 · Accepted Answer · answered Jun 23 '16 at 05:58

I already fixed this. The problem is that modelsim couldn't find the .txt file, I don't know where could be the predetermined location for such of files, but looking in internet, I found that I can declare in the Ram module, the exact path like this

initial
begin
$readmemb("C:/altera/15.0/Prueba5/in_ram.txt", in_ram);
end

Now modelsim is loading the correct data. Thanks everybody.

score 0 · Answer 3 · answered May 06 '20 at 22:33

0

Pasting a copy of the initialization data file (e.g. "in_ram.txt") into the project's ..\simulation\modelsim\ directory also resolved this issue for me.

answered May 06 '20 at 22:33

isaiah

1

score 0 · Answer 4 · edited Mar 08 '21 at 10:50

0

I was getting the same issue. It was due to other than binary characters present in the file.

Initially my .txt file was looking like .txt file I am reading

.txt file I am reading

Then I removed all the "-" and it worked. Please check .txt file once if any character is misprinted.

edited Mar 08 '21 at 10:50

sahasrara62

10,069
3
29
44

answered Mar 04 '21 at 05:42

Neel Joshi

37
4

In Verilog, I'm trying to use $readmemb to read .txt file but it only loads xxxxx (dont cares) on memory

4 Answers4