Reading Files in VHDL

Here’s the translation of the Go code example to VHDL, formatted in Markdown suitable for Hugo:

Our first program will demonstrate file reading operations in VHDL. Here’s the full source code:

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

entity FileReader is
end FileReader;

architecture Behavioral of FileReader is
begin
    process
        file input_file : text;
        variable file_line : line;
        variable file_char : character;
        variable read_status : boolean;
    begin
        -- Open the file for reading
        file_open(input_file, "/tmp/dat", read_mode);
        
        -- Read the entire file contents
        while not endfile(input_file) loop
            readline(input_file, file_line);
            write(output, file_line.all);
            writeline(output, file_line);
        end loop;
        
        -- Close and reopen the file for specific operations
        file_close(input_file);
        file_open(input_file, "/tmp/dat", read_mode);
        
        -- Read first 5 characters
        for i in 1 to 5 loop
            read(file_line, file_char, read_status);
            if read_status then
                write(output, file_char);
            end if;
        end loop;
        writeline(output, file_line);
        
        -- Seek to a specific position (6th character)
        readline(input_file, file_line);
        for i in 1 to 5 loop
            read(file_line, file_char);
        end loop;
        
        -- Read 2 characters from current position
        for i in 1 to 2 loop
            read(file_line, file_char, read_status);
            if read_status then
                write(output, file_char);
            end if;
        end loop;
        writeline(output, file_line);
        
        -- Close the file
        file_close(input_file);
        
        wait;
    end process;
end Behavioral;

This VHDL code demonstrates basic file reading operations. Here’s a breakdown of what it does:

It opens a file named “/tmp/dat” for reading.
It reads and prints the entire contents of the file.
It then closes and reopens the file to perform more specific operations.
It reads the first 5 characters of the file.
It seeks to the 6th character and reads 2 characters from that position.
Finally, it closes the file.

Note that VHDL doesn’t have built-in functions for all the operations we saw in the original example, so we’ve simulated some of them using basic file reading and writing operations.

To run this VHDL code, you would typically use a VHDL simulator like ModelSim or GHDL. The exact commands would depend on your specific environment and toolchain.

It’s important to note that file I/O in VHDL is primarily used for simulation purposes and is not synthesizable for actual hardware. In real FPGA or ASIC designs, you would typically use other methods for data input and output.

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Reading Files in VHDL