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-- File Name :  ByteStuffer.vhd

--

-- Project   : JPEG_ENC

--

-- Module    : ByteStuffer

--

-- Content   : ByteStuffer

--

-- Description : ByteStuffer core

--

-- Spec.     : 

--

-- Author    : Michal Krepa

--

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-- History :

-- 20090301: (MK): Initial Creation.

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----------------------------------- LIBRARY/PACKAGE ---------------------------

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-- generic packages/libraries:

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library ieee;

  use ieee.std_logic_1164.all;

  use ieee.numeric_std.all;

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-- user packages/libraries:

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library work;

  use work.JPEG_PKG.all;

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----------------------------------- ENTITY ------------------------------------

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entity ByteStuffer is

  port

  (

        CLK                : in  std_logic;

        RST                : in  std_logic;

        -- CTRL

        start_pb           : in  std_logic;

        ready_pb           : out std_logic;

        -- HOST IF

        sof                : in  std_logic;

        num_enc_bytes      : out std_logic_vector(23 downto 0);

        outram_base_addr   : in  std_logic_vector(9 downto 0);

        -- Huffman

        huf_buf_sel        : out std_logic;

        huf_fifo_empty     : in  std_logic;

        huf_rd_req         : out std_logic;

        huf_packed_byte    : in  std_logic_vector(7 downto 0);

        -- OUT RAM

        ram_byte           : out std_logic_vector(7 downto 0);

        ram_wren           : out std_logic;

        ram_wraddr         : out std_logic_vector(23 downto 0)

    );

end entity ByteStuffer;

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----------------------------------- ARCHITECTURE ------------------------------

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architecture RTL of ByteStuffer is

  signal huf_data_val   : std_logic_vector(3 downto 0);

  signal wdata_reg      : std_logic_vector(15 downto 0);

  signal wraddr         : unsigned(23 downto 0);

  signal wr_n_cnt       : unsigned(1 downto 0);

  signal huf_buf_sel_s  : std_logic;

  signal rd_en          : std_logic;

  signal rd_en_d1       : std_logic;

  signal huf_rd_req_s   : std_logic;

  signal latch_byte     : std_logic_vector(7 downto 0);

  signal data_valid     : std_logic;

  signal wait_for_ndata : std_logic;

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-- Architecture: begin

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begin

  huf_buf_sel <= huf_buf_sel_s;

  huf_rd_req  <= huf_rd_req_s;

  num_enc_bytes <= std_logic_vector(wraddr);

  -------------------------------------------------------------------

  -- CTRL_SM

  -------------------------------------------------------------------

  p_ctrl_sm : process(CLK, RST)

  begin

    if RST = '1' then

      wr_n_cnt     <= (others => '0');

      ready_pb     <= '0';

      huf_rd_req_s <= '0';

      huf_data_val <= (others => '0');

      rd_en        <= '0';

      rd_en_d1     <= '0';

      wdata_reg    <= (others => '0');

      ram_wren     <= '0';

      wraddr       <= (others => '0');

      ram_wraddr   <= (others => '0');

      ram_byte     <= (others => '0');

      latch_byte   <= (others => '0');

      wait_for_ndata <= '0';

      data_valid     <= '0';

    elsif CLK'event and CLK = '1' then

      huf_rd_req_s <= '0';

      ready_pb     <= '0';

      huf_data_val <= huf_data_val(huf_data_val'length-2 downto 0) & huf_rd_req_s;

      rd_en_d1     <= rd_en;

      ram_wren     <= '0';

      data_valid   <= '0';

      if start_pb = '1' then

        rd_en <= '1';

      end if;

      -- read FIFO until it becomes empty. wait until last byte read is

      -- serviced

      if rd_en_d1 = '1' and wait_for_ndata = '0' then

        -- FIFO empty

        if huf_fifo_empty = '1' then

          rd_en      <= '0';

          rd_en_d1   <= '0';

          ready_pb   <= '1';

        else

          huf_rd_req_s <= '1';

          wait_for_ndata <= '1';

        end if;

      end if;

      -- show ahead FIFO, capture data early

      if huf_rd_req_s = '1' then

        latch_byte <= huf_packed_byte;

        data_valid <= '1';

      end if;

      if huf_data_val(1) = '1' then

        wait_for_ndata <= '0';

      end if;

      -- data from FIFO is valid

      if data_valid = '1' then

        -- stuffing necessary

        if latch_byte = X"FF" then

          -- two writes are necessary for byte stuffing

          wr_n_cnt  <= "10";

          wdata_reg <= X"FF00";

        -- no stuffing

        else

          wr_n_cnt  <= "01";

          wdata_reg <= X"00" & latch_byte;

        end if;

      end if;

      if wr_n_cnt > 0 then

        wr_n_cnt <= wr_n_cnt - 1;

        ram_wren <= '1';

        wraddr   <= wraddr + 1;

      end if;

      -- delayed to make address post-increment

      ram_wraddr <= std_logic_vector(wraddr);

      -- stuffing

      if wr_n_cnt = 2 then

        ram_byte <= wdata_reg(15 downto 8);

      elsif wr_n_cnt = 1 then

        ram_byte <= wdata_reg(7 downto 0);

      end if;

      if sof = '1' then

        wraddr <= to_unsigned(C_HDR_SIZE,wraddr'length);

      end if;

    end if;

  end process;

  -------------------------------------------------------------------

  -- HUFFMAN buf_sel

  -------------------------------------------------------------------

  p_huf_buf_sel : process(CLK, RST)

  begin

    if RST = '1' then

      huf_buf_sel_s   <= '0';

    elsif CLK'event and CLK = '1' then

      if start_pb = '1' then

        huf_buf_sel_s <= not huf_buf_sel_s;

      end if;

    end if;

  end process;

end architecture RTL;

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-- Architecture: end

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