Writing Files in VHDL

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

Writing files in VHDL follows similar patterns to the ones we saw earlier for reading.

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

entity file_writer is
end file_writer;

architecture Behavioral of file_writer is
begin
    process
        file output_file: TEXT;
        variable line_out: LINE;
    begin
        -- To start, here's how to dump a string into a file.
        file_open(output_file, "dat1.txt", WRITE_MODE);
        write(line_out, string'("hello" & LF & "vhdl"));
        writeline(output_file, line_out);
        file_close(output_file);

        -- For more granular writes, open a file for writing.
        file_open(output_file, "dat2.txt", WRITE_MODE);

        -- You can write strings as you'd expect.
        write(line_out, string'("some"));
        writeline(output_file, line_out);

        -- A write is also available for other types.
        write(line_out, integer'(42));
        writeline(output_file, line_out);

        -- VHDL doesn't have a built-in concept of buffered writers,
        -- but you can implement your own buffering mechanism if needed.

        file_close(output_file);

        wait;
    end process;
end Behavioral;

Let’s break down the code and explain its parts:

1. We start by importing necessary libraries for file I/O operations in VHDL.

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

3. Inside the architecture, we have a process that performs file writing operations.

4. We declare a file handle output_file of type TEXT and a line variable line_out to hold the data we want to write.

5. To write a string to a file:

   • We open the file “dat1.txt” in write mode.
   • We use the write procedure to write a string to line_out.
   • We use writeline to write the contents of line_out to the file.
   • We close the file after writing.

6. For more granular writes:

   • We open another file “dat2.txt”.
   • We write a string “some” to the file.
   • We write an integer 42 to the file.

7. VHDL doesn’t have a built-in buffered writer like Go’s bufio. If you need buffering, you would need to implement it yourself.

8. We close the file after all write operations are complete.

9. The wait statement at the end of the process is necessary in VHDL simulations to prevent the process from restarting indefinitely.

To run this VHDL code, you would typically use a VHDL simulator. The exact commands would depend on your specific simulation environment.

After running the simulation, you can check the contents of the written files:

$ cat dat1.txt
hello
vhdl
$ cat dat2.txt
some
42

Note that VHDL is primarily used for hardware description and simulation, so file I/O operations are mainly used for simulation and testing purposes, not in synthesized hardware.