Logging in VHDL

Here’s an idiomatic VHDL example that demonstrates a simple logging concept:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity LoggingExample is
    port (
        clk     : in  std_logic;
        reset   : in  std_logic;
        data_in : in  std_logic_vector(7 downto 0);
        log_out : out std_logic_vector(7 downto 0)
    );
end entity LoggingExample;

architecture Behavioral of LoggingExample is
    -- Define a type for log levels
    type log_level_t is (DEBUG, INFO, WARNING, ERROR);
    
    -- Function to convert log level to std_logic_vector
    function log_level_to_slv(level : log_level_t) return std_logic_vector is
    begin
        case level is
            when DEBUG   => return x"00";
            when INFO    => return x"01";
            when WARNING => return x"02";
            when ERROR   => return x"03";
        end case;
    end function;

    -- Procedure for logging
    procedure log(level : log_level_t; message : std_logic_vector(7 downto 0)) is
    begin
        report "Log: " & to_string(level) & " - Data: " & to_hstring(message);
    end procedure;

begin
    process(clk, reset)
    begin
        if reset = '1' then
            log_out <= (others => '0');
        elsif rising_edge(clk) then
            -- Log the input data
            log(INFO, data_in);
            
            -- Output the logged data with a level indicator
            log_out <= log_level_to_slv(INFO) & data_in(7 downto 1);
        end if;
    end process;

end architecture Behavioral;

This VHDL example demonstrates a simple logging concept, which is analogous to the logging functionality shown in the original Go example. Here’s an explanation of the code:

1. We define an entity LoggingExample with clock, reset, input data, and output log ports.

2. In the architecture, we define a custom type log_level_t to represent different log levels (DEBUG, INFO, WARNING, ERROR).

3. We create a function log_level_to_slv to convert the log level to a std_logic_vector representation.

4. A log procedure is defined to simulate logging by using the VHDL report statement. This is similar to print statements in software languages.

5. In the main process, we demonstrate logging the input data on each clock cycle:

   • We use the log procedure to output the data with an INFO level.
   • We also prepare an output that combines the log level and the input data.

To use this code:

1. Save it in a file with a .vhd extension, e.g., logging_example.vhd.
2. Compile it using a VHDL compiler, such as GHDL:

   ghdl -a logging_example.vhd
   ghdl -e LoggingExample

3. You can then simulate it using a testbench or integrate it into a larger VHDL project.

Note that VHDL, being a hardware description language, doesn’t have built-in file I/O or console output like software languages. The report statement is used for simulation purposes. In actual hardware, you would typically use the log_out signal to transmit log information to other parts of your design or to external interfaces.

This example demonstrates how to implement a basic logging concept in VHDL, adapting the idea to fit within the constraints and paradigms of hardware description languages.