Execing Processes in VHDL

Here’s the translation of the Go code to VHDL, with explanations in Markdown format suitable for Hugo:

Our example demonstrates how to execute an external process in VHDL. While VHDL is primarily used for hardware description and doesn’t have direct system call capabilities like software languages, we can simulate the concept using VHDL’s file I/O operations and system functions.

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

entity ExecProcess is
end ExecProcess;

architecture Behavioral of ExecProcess is
begin
    process
        file output_file : TEXT;
        variable line_out : LINE;
        variable command_result : LINE;
    begin
        -- Simulate finding the binary path
        write(line_out, string'("Found binary: /bin/ls"));
        writeline(output, line_out);
        
        -- Simulate setting up arguments
        write(line_out, string'("Arguments: -a -l -h"));
        writeline(output, line_out);
        
        -- Simulate executing the command
        write(line_out, string'("Executing: /bin/ls -a -l -h"));
        writeline(output, line_out);
        
        -- Simulate command output
        file_open(output_file, "command_output.txt", WRITE_MODE);
        write(command_result, string'("total 16"));
        writeline(output_file, command_result);
        write(command_result, string'("drwxr-xr-x  4 user 136B Oct 3 16:29 ."));
        writeline(output_file, command_result);
        write(command_result, string'("drwxr-xr-x 91 user 3.0K Oct 3 12:50 .."));
        writeline(output_file, command_result);
        write(command_result, string'("-rw-r--r--  1 user 1.3K Oct 3 16:28 exec_process.vhd"));
        writeline(output_file, command_result);
        file_close(output_file);
        
        -- Simulation complete
        write(line_out, string'("Command execution simulated"));
        writeline(output, line_out);
        
        wait;
    end process;
end Behavioral;

In this VHDL example, we simulate the process of executing an external command. Since VHDL doesn’t have direct system call capabilities, we use file I/O operations to demonstrate the concept.

1. We start by including necessary libraries for text I/O operations.

2. In the process, we first simulate finding the binary path by writing a message to the console.

3. We then simulate setting up the arguments for the command.

4. To simulate the execution of the command, we write a message indicating that the command is being executed.

5. Instead of actually executing the command, we write the simulated output to a file named “command_output.txt”. This represents the result we would get from executing the “ls -a -l -h” command.

6. Finally, we indicate that the command execution has been simulated.

To run this VHDL code, you would typically use a VHDL simulator such as ModelSim or GHDL. The simulator would execute the process and you would see the output in the simulator’s console, and the simulated command output would be written to the “command_output.txt” file.

$ ghdl -a exec_process.vhd
$ ghdl -e ExecProcess
$ ghdl -r ExecProcess
Found binary: /bin/ls
Arguments: -a -l -h
Executing: /bin/ls -a -l -h
Command execution simulated

Note that this is a simulation of the concept rather than actual system execution. VHDL, being a hardware description language, doesn’t have the capability to directly execute system commands like software programming languages do.