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.

Yulan

Modelsim will read and write binary files generated by itself or another application. How you interpret the bits is up to your code. – Noctambulism

I know I can read any file, interpreting it as 8 bit sections was the problem. – Yulan

Answer 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.

Pepe

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

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. – Pepe

What language would you suggest? Perl/Python? – Yulan

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

Answer 2

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;

Yulan

Answer 3

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;

Strikebreaker