GammaStack.vhdl

-- Empty descending stack implementation in VHDL.
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity GammaStack is
    port (
        Clk : in std_logic;      -- Clock for the stack.
        Reset : in std_logic;    -- Active high reset.
        Enable : in std_logic;   -- Enable the stack. Otherwise neither push nor pop will happen.
        Data_In : in std_logic_vector(31 downto 0);    -- Data to be pushed to stack.
        Data_Out : out std_logic_vector(31 downto 0);  -- Data popped from the stack.
        Push_Mode : in std_logic;    -- Active low for POP and active high for PUSH.
        Stack_Full : out std_logic;    -- Goes high when the stack is full.
        Stack_Empty : out std_logic;   -- Goes high when the stack is empty.
        Debug_Dump : in std_logic    -- Dump the stack for debugging.
    );
end GammaStack;

architecture Behavioral of GammaStack is
    type stack is array (0 to 31) of std_logic_vector(31 downto 0);  -- Stack of 32 elements.
    signal Stack_Reg : stack;  -- Signal to hold the stack.
    signal Top : integer range 0 to 31 := 0;  -- Top of the stack.
begin
    process(Clk, Reset)
    begin
        -- print the entire stack
        if Debug_Dump = '1' then
            for i in 0 to 31 loop
                if to_string(Stack_Reg(i)) /= "UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU" then 
                    report "pos: " & integer'image(i);
                    report "value: " & to_string(Stack_Reg(i));
                end if;
            end loop;
        end if;
        if Reset = '1' then
            Top <= 0;
            Stack_Empty <= '1';
            Stack_Full <= '0';
        elsif rising_edge(Clk) then
            if Enable = '1' then
                if Push_Mode = '0' then  -- POP
                    if Top = 0 then
                        Stack_Empty <= '1';
                    else
                        Data_Out <= Stack_Reg(Top - 1);
                        Stack_Empty <= '0';
                        Top <= Top - 1;
                    end if;
                else  -- PUSH
                    if Top = 31 then
                        Stack_Full <= '1';
                    else
                        Stack_Full <= '0';
                        Stack_Empty <= '0';
                        Top <= Top + 1;
                        Stack_Reg(Top) <= Data_In;
                    end if;
                end if;
            end if;
        end if;
    end process;
end Behavioral;