library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

----------------------RAM Entity---------------------------
entity Single_Port_RAM is
    port(
        clk               : in  std_logic; 
        rst               : in  std_logic;
        Address_bus       : in  std_logic_vector(7 downto 0); --From DMA
        Read_write_Enable : in  std_logic_vector(1 downto 0); --From DMA
        Data_bus_in       : in  std_logic_vector(7 downto 0); --From Noc
        Data_bus_out      : out std_logic_vector(7 downto 0)  --From Noc
        );
end entity;

----------------------RAM Behaviour------------------------
architecture Single_Port_RAM_behav of Single_Port_RAM is

   ------- define the new type for the 128x8 RAM 
   type RAM_ARRAY is array (0 to 127 ) of std_logic_vector (7 downto 0);
   -------- initial values in the RAM to X00
   signal RAM: RAM_ARRAY := (others=>x"00"); 
   signal initialized : std_logic; -- Initialization flag

begin
    process(clk, rst)
    begin
        if rst = '0' then -- inverted reset
            Data_bus_out <= (others => '0');
            initialized <= '1';
        elsif rising_edge(clk) then
    --Setting value to the RAM to coresponding index   
            if initialized = '1' then
                for i in 0 to 127 loop
                    RAM(i) <= std_logic_vector(to_unsigned(i,8));
                end loop;
                initialized <= '0';
            end if;
    --Read Write functionality of RAM
            if (Read_write_Enable(0) = '0' and Read_write_Enable(1) = '1' )then               --read enable; [MSB] READ Enable [LSB] WRITE Enable  
                Data_bus_out <=  RAM(to_integer(unsigned(Address_bus(6 downto 0 ))));         -- read data from RAM 
            elsif (Read_write_Enable(0) = '1' and Read_write_Enable(1) = '0') then             --write enable; [MSB] READ Enable [LSB] WRITE Enable 
                RAM(to_integer(unsigned(Address_bus(6 downto 0)))) <= Data_bus_in(7 downto 0); -- Write data to RAM
                Data_bus_out <= (others => '0');
            else
                Data_bus_out <= (others => '0');
            end if;
        end if;
    end process;
end architecture;