Directories in VHDL

Here’s an idiomatic VHDL example that demonstrates working with directories:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
use STD.TEXTIO.ALL;
use IEEE.STD_LOGIC_TEXTIO.ALL;

entity directory_operations is
end directory_operations;

architecture Behavioral of directory_operations is
begin
    process
        file input_file : text;
        file output_file : text;
        variable file_line : line;
        variable file_status : file_open_status;
        variable dir_name : string(1 to 20) := "simulation_results/";
        variable file_name : string(1 to 15) := "output_data.txt";
    begin
        -- Create a directory
        report "Creating directory: " & dir_name;
        file_open(file_status, output_file, dir_name & file_name, write_mode);
        
        if file_status = open_ok then
            report "Directory created successfully";
        else
            report "Failed to create directory" severity error;
        end if;
        
        -- Write some data to the file
        write(file_line, string'("Simulation data"));
        writeline(output_file, file_line);
        
        -- Close the file
        file_close(output_file);
        
        -- Read from the file
        file_open(file_status, input_file, dir_name & file_name, read_mode);
        
        if file_status = open_ok then
            report "Reading from file: " & dir_name & file_name;
            while not endfile(input_file) loop
                readline(input_file, file_line);
                report file_line.all;
            end loop;
        else
            report "Failed to open file for reading" severity error;
        end if;
        
        -- Close the file
        file_close(input_file);
        
        wait;
    end process;
end Behavioral;

This VHDL code demonstrates basic directory and file operations, which is the closest equivalent to the directory operations shown in the original Go example. Here’s an explanation of the code:

1. We start by including necessary libraries, especially STD.TEXTIO and IEEE.STD_LOGIC_TEXTIO for file operations.

2. We define an entity directory_operations and its architecture Behavioral.

3. Inside the architecture, we have a process that performs file and directory operations:

   • We declare file handles, a line variable for reading/writing, and variables for directory and file names.

   • To create a directory, we attempt to open a file in that directory. If successful, it implies the directory exists or was created.

   • We write some data to the file using write and writeline functions.

   • We then close the file and reopen it for reading.

   • We read the contents of the file using a while loop and the readline function, reporting each line.

4. Error handling is done using VHDL’s report statements, which is similar to printing errors in other languages.

5. The wait statement at the end of the process ensures it runs only once during simulation.

It’s important to note that VHDL, being a hardware description language, doesn’t have built-in support for creating directories or listing directory contents like Go does. File operations in VHDL are primarily used for simulation purposes, reading test vectors, or writing simulation results.

To use this code:

1. Save it in a file with a .vhd extension, e.g., directory_operations.vhd.
2. Compile and simulate it using a VHDL simulator like ModelSim, GHDL, or Vivado Simulator.
3. The simulator will create the directory and file as specified in the code, and you’ll see the reported messages in the simulator console.

Remember that the actual creation of directories and files happens in the simulation environment, not on real hardware. In real FPGA implementations, file operations are typically not synthesizable and are used only for simulation and testing purposes.