Line Filters in VHDL

Here’s the translation of the Go line filter program to VHDL, along with explanations in Markdown format suitable for Hugo:

A line filter is a common type of program that reads input, processes it, and then prints some derived result. In VHDL, we can implement a similar concept using file I/O operations.

Here’s an example line filter in VHDL that reads input text, converts it to uppercase, and writes the result. You can use this pattern to write your own VHDL line filters.

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

entity line_filter is
end line_filter;

architecture Behavioral of line_filter is
begin
    process
        file input_file : text;
        file output_file : text;
        variable input_line : line;
        variable output_line : line;
        variable char : character;
    begin
        file_open(input_file, "input.txt", read_mode);
        file_open(output_file, "output.txt", write_mode);
        
        while not endfile(input_file) loop
            readline(input_file, input_line);
            
            for i in 1 to input_line'length loop
                read(input_line, char);
                if char >= 'a' and char <= 'z' then
                    char := character'val(character'pos(char) - 32);
                end if;
                write(output_line, char);
            end loop;
            
            writeline(output_file, output_line);
        end loop;
        
        file_close(input_file);
        file_close(output_file);
        
        wait;
    end process;
end Behavioral;

This VHDL code reads from an input file named “input.txt”, processes each line by converting it to uppercase, and writes the result to an output file named “output.txt”.

To try out our line filter:

1. Create an input file named “input.txt” with a few lowercase lines.

$ echo 'hello' > input.txt
$ echo 'filter' >> input.txt

2. Compile and run the VHDL code using your preferred VHDL simulator.

3. Check the contents of the output file “output.txt”.

$ cat output.txt
HELLO
FILTER

This VHDL implementation differs from the original in several ways:

1. It uses file I/O instead of standard input/output, as VHDL is typically used for hardware description and simulation rather than interactive console programs.

2. The uppercase conversion is done character by character, as VHDL doesn’t have built-in string manipulation functions like in high-level programming languages.

3. Error handling is not explicitly implemented in this example, as error handling in VHDL is typically done through assertion statements or custom error reporting mechanisms, which would depend on the specific simulation environment.

Remember that VHDL is primarily used for hardware description and simulation, so this example is more conceptual and might not be practical for real-world text processing tasks.