How can I read binary data in VHDL/modelsim whithout using special binary formats

Question

I am writing a VHDL test bench for a ethernet MAC. The testbench consists of a package and an combined entity + architecture file. I want to read the ethernet frames that the testbench will send to the MAC from a binary file which I exported from wireshark.

I'm writing in VHDL 2008 and I'm using a Mentor Graphics Model Technology ModelSim ALTERA vcom 10.0d Compiler.

All solutions for reading binary data in VHDL/modelsim that I've found so far use special file formats where 1 bit of the bit_vector is represented by several bits in the file. I would like VHDL to read the binary file into 8 bit bit_vectors.

Closest I've gotten so far was using a character type file, where I can write 8 bit ASCII characters directly in binary representation.

Modelsim will read and write binary files generated by itself or another application. How you interpret the bits is up to your code. — user1818839
– user1818839, Commented Jan 5, 2013 at 22:05
I know I can read any file, interpreting it as 8 bit sections was the problem. — youR.Fate
– youR.Fate, Commented Jan 8, 2013 at 13:03

mkrieger1 · Accepted Answer · 2022-03-21 16:36:09Z

4

To interpret the data directly in 8 bit parts, you need to use a file of the type character and convert them to integers using the 'POS attribute. You can then convert these integers to bit vectors:

LIBRARY ieee;
  USE ieee.std_logic_1164.ALL;
  USE ieee.numeric_bit.ALL;

LIBRARY std;
  USE std.textio.all;

...

TYPE t_char_file IF FILE OF character;
TYPE t_byte_arr IS ARRAY (natural RANGE <>) OF bit_vector(7 DOWNTO 0);

SIGNAL read_arr_byte : t_byte_arr(0 to 199);

...

read_file: PROCESS (start) IS
  FILE file_in : t_char_file OPEN read_mode IS "./38478.bin";  -- open the frame file for reading
  VARIABLE char_buffer : character;
BEGIN
  IF start'EVENT AND start = '1' THEN
    FOR i IN read_arr_byte'RANGE LOOP
      read(file_in, char_buffer);
      read_arr_byte(i) <= bit_vector(to_unsigned(character'POS(char_buffer), 8));
    END LOOP;  -- i
    file_close(file_in);
  END IF;
END PROCESS read_file;

edited Mar 21, 2022 at 16:36

mkrieger1

24.2k7 gold badges68 silver badges84 bronze badges

answered Jan 8, 2013 at 12:59

youR.Fate

8364 gold badges11 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Martin Thompson · Accepted Answer · 2013-01-08 14:10:15Z

1

I used to do this, but have found it more productive to write a short script (in a serious text processing language) to convert from whatever input to a real VHDL file with the data described as a constant array of a suitable datatype.

This is much easier than doing file parsing in VHDL IMHO.

answered Jan 8, 2013 at 14:10

Martin Thompson

16.9k1 gold badge40 silver badges58 bronze badges

4 Comments

youR.Fate Over a year ago

Yes, but I don't need to process the data much, I read it into arrays which I push into a linked list stack.

Martin Thompson Over a year ago

Even so, I'd avoid reading files in VHDL, and just write the VHDL arrays with a language designed for the job of reading files well.

youR.Fate Over a year ago

What language would you suggest? Perl/Python?

Martin Thompson Over a year ago

Python is my language of choice for conversions. I also use Matlab for image processing development and write out "golden-data" in VHDL files

EquipDev · Accepted Answer · 2017-03-03 14:48:15Z

1

Based on previous answer from @youR.Fate, I was able to reduce the example further to:

process is
  type char_file_t is file of character;
  file char_file : char_file_t;
  variable char_v : character;
  subtype byte_t is natural range 0 to 255;
  variable byte_v : byte_t;
begin
  file_open(char_file, "test.bin");
  while not endfile(char_file) loop
    read(char_file, char_v);
    byte_v := character'pos(char_v);
    report "Char: " & " #" & integer'image(byte_v);
  end loop;
  file_close(char_file);
  wait;
end process;

answered Mar 3, 2017 at 14:48

EquipDev

6,06111 gold badges43 silver badges77 bronze badges

Collectives™ on Stack Overflow

How can I read binary data in VHDL/modelsim whithout using special binary formats

3 Answers 3

Comments

4 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related