Subversion Repositories ccsds_rxtxsoc

---- Design Name: ccsds_tx_coder_differential

---- Version: 1.0.0

---- Description:

---- Word by word differential coder

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

---- Author(s):

---- Guillaume REMBERT

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

---- Licence:

---- MIT

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---- Changes list:

---- 2016/11/18: initial release

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

-- libraries used

library ieee;

use ieee.std_logic_1164.all;

--=============================================================================

-- Entity declaration for ccsds_tx / unitary tx differential coder inputs and outputs

--=============================================================================

entity ccsds_tx_coder_differential is

  generic(

    constant CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD: integer;

    constant CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE: integer -- in bits

  );

  port(

    -- inputs

    clk_i: in std_logic;

    dat_i: in std_logic_vector(CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE-1 downto 0);

    dat_val_i: in std_logic;

    rst_i: in std_logic;

    -- outputs

    dat_o: out std_logic_vector(CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE-1 downto 0);

    dat_val_o: out std_logic

  );

end ccsds_tx_coder_differential;

--=============================================================================

-- architecture declaration / internal components and connections

--=============================================================================

architecture rtl of ccsds_tx_coder_differential is

-- internal constants

-- internal variable signals

-- components instanciation and mapping

  begin

-- presynthesis checks

     CHKCODERP0 : if (CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE mod (CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD) /= 0) generate

      process

      begin

        report "ERROR: DATA BUS SIZE HAS TO BE A MULTIPLE OF BITS PER CODE WORD" severity failure;

              wait;

      end process;

    end generate CHKCODERP0;

-- internal processing

    --=============================================================================

    -- Begin of coderdiffp

    -- Differential encode words

    --=============================================================================

    -- read: rst_i, dat_i, dat_val_i

    -- write: dat_o, dat_val_o

    -- r/w:

    CODERDIFFP: process (clk_i)

    variable prev_sym: std_logic_vector(CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD-1 downto 0) := (others => '0');

    begin

      -- on each clock rising edge

      if rising_edge(clk_i) then

        -- reset signal received

        if (rst_i = '1') then

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

          dat_val_o <= '0';

          prev_sym := (others => '0');

        else

          if (dat_val_i = '1') then

            dat_val_o <= '1';

            dat_o(CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE-1 downto CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE-CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD) <= prev_sym xor dat_i(CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE-1 downto CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE-CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD);

            for i in CCSDS_TX_CODER_DIFF_DATA_BUS_SIZE/(CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD)-1 downto 1 loop

              dat_o(i*CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD-1 downto (i-1)*CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD) <= dat_i(i*CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD-1 downto (i-1)*CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD) xor dat_i((i+1)*CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD-1 downto i*CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD);

            end loop;

            prev_sym := dat_i(CCSDS_TX_CODER_DIFF_BITS_PER_CODEWORD-1 downto 0);

          else

            dat_val_o <= '0';

          end if;

        end if;

      end if;

    end process;

end rtl;