Arrays in VHDL

In VHDL, an array is a collection of elements of the same type. Arrays are commonly used in VHDL for various purposes, including signal and variable declarations.

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

entity ArrayExample is
end ArrayExample;

architecture Behavioral of ArrayExample is
    -- Function to convert integer array to string for printing
    function int_array_to_string(arr: in integer_vector) return string is
        variable result : string(1 to arr'length * 4);
        variable idx : integer := 1;
    begin
        for i in arr'range loop
            result(idx to idx+3) := integer'image(arr(i));
            idx := idx + 4;
        end loop;
        return result;
    end function;

    -- Declare an array of 5 integers
    type int_array is array (0 to 4) of integer;
    signal a : int_array := (others => 0);

begin
    process
        -- Declare and initialize an array in one line
        variable b : int_array := (1, 2, 3, 4, 5);
        
        -- 2D array declaration
        type int_array_2d is array (0 to 1, 0 to 2) of integer;
        variable twoD : int_array_2d := ((0, 0, 0), (0, 0, 0));
    begin
        -- Print the initial array
        report "emp: " & int_array_to_string(a);

        -- Set a value at an index
        a(4) <= 100;
        wait for 10 ns;  -- Wait for the signal to update
        report "set: " & int_array_to_string(a);
        report "get: " & integer'image(a(4));

        -- Print the length of the array
        report "len: " & integer'image(a'length);

        -- Print the initialized array
        report "dcl: " & int_array_to_string(b);

        -- Initialize 2D array
        for i in 0 to 1 loop
            for j in 0 to 2 loop
                twoD(i, j) := i + j;
            end loop;
        end loop;

        -- Print 2D array
        report "2d: " & int_array_to_string(twoD(0, 0 to 2)) & " " &
                        int_array_to_string(twoD(1, 0 to 2));

        -- Re-initialize 2D array
        twoD := ((1, 2, 3), (1, 2, 3));
        report "2d: " & int_array_to_string(twoD(0, 0 to 2)) & " " &
                        int_array_to_string(twoD(1, 0 to 2));

        wait;
    end process;
end Behavioral;

In this VHDL example:

We define a custom type int_array to create an array of 5 integers.
We create a signal a of type int_array and initialize it with zeros.
We define a function int_array_to_string to convert our integer arrays to strings for reporting, as VHDL doesn’t have built-in array printing.
We demonstrate setting and getting values from the array.
We show how to get the length of an array using the 'length attribute.
We create and initialize an array b in one line.
We create a 2D array twoD and show how to initialize and access it.
We use the report statement to print our results, which is similar to fmt.Println in Go.

Note that VHDL is primarily used for hardware description, so concepts like dynamic memory allocation or resizable arrays are not applicable. The arrays in VHDL are fixed-size and determined at compile time.

To simulate this VHDL code, you would typically use a VHDL simulator like ModelSim or GHDL. The output would appear in the simulator’s console, showing the various array operations and their results.

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Arrays in VHDL