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--This library is free software; you can redistribute it and/or

--modify it under the terms of the GNU Lesser General Public

--License as published by the Free Software Foundation; either

--version 2.1 of the License, or (at your option) any later version.

--This library is distributed in the hope that it will be useful,

--but WITHOUT ANY WARRANTY; without even the implied warranty of

--MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

--Lesser General Public License for more details.

--You should have received a copy of the GNU Lesser General Public

--License along with this library; if not, write to the Free Software

--Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

-- e_mail : j.l.nunez-yanez@byacom.co.uk

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

--  ENTITY       = DECODING_BUFFER_CU              --

--  version      = 1.0                             --

--  last update  = 16/6/00                         --

--  author       = Jose Nunez                      --

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

-- FUNCTION

-- Control unit that controls the decoding buffer

--  PIN LIST

--  START : enable writting to the buffer

--  FINISHED : the block has been process in the decompression engine stop requesting data.

--  UNDERFLOW : 64 bit of compressed data are needed.

--  THRESHOLD : more data is available in the buffer to be decompressed than the threshold limit.

--  CODING_READ_ADDRESS : buffer location that it is being read

--  CODING_WRITE_ADDRESS : buffer location that it is being written

--  CLK : clock

--  CLEAR : clear

--  BUS_REQUEST : more compressed data is required if after getting data the bus is denied and data is in the internal buffer stop requesting.

--  CODING_OVERFLOW : the CU detects a coding overflow stop inputting compressed data 

--  CODING_UNDERFLOW : the CU detects a coding underflow stop outputting compressed data

--  ENABLE_WRITE : enable writting to the buffer

--  FINISH : the buffer process

--  ENABLE_READ : enable reading from the buffer

library ieee;

use ieee.std_logic_1164.all;

library dzx;

use dzx.bit_arith.all;

use dzx.bit_utils.all;

entity DECODING_BUFFER_CU_2 is

port

(

    FORCE_STOP : in bit;

          START_D : in bit;  --  enter decompression mode

          START_C : in bit;  --  enter test mode since compression is active

          FINISHED_D : in bit; --  finish decompression mode

          FINISHED_C : in bit; -- finish test mode

          UNDERFLOW : in bit; -- the engine requests data

          BUS_ACKNOWLEDGE : in bit;

                WAITN : in bit; -- wait states being introduced

          C_DATA_VALID : in bit; -- compressed data available in test mode

          THRESHOLD_LEVEL : in bit_vector(9 downto 0);

          DECODING_READ_ADDRESS : in bit_vector(9 downto 0);

          DECODING_WRITE_ADDRESS : in bit_vector(9 downto 0);

          CLK : in bit;

          CLEAR : in bit;

          BUS_REQUEST : out bit;

          DECODING_UNDERFLOW : out bit;

          ENABLE_WRITE : out bit;

          FINISH : out bit; -- the buffer process

          CLEAR_COUNTERS : out bit;

    OVERFLOW_CONTROL : out bit;

          ENABLE_READ : out bit

);

end DECODING_BUFFER_CU_2;

architecture STRUCTURAL of DECODING_BUFFER_CU_2 is

signal CURRENT_STATE : bit_vector(3 downto 0);

signal NEXT_STATE : bit_vector(3 downto 0);

signal DECODING_OVERFLOW_AUX : bit;

signal DECODING_UNDERFLOW_AUX : bit;

signal ENABLE_READ_INT : bit;

signal DECODING_UNDERFLOW_INT : bit; -- to hold underflow until threshold is overpassed

signal ENABLE_WRITE_INT : bit;

signal BUS_ACKNOWLEDGE_INT : bit;

signal BUS_REQUEST_INT : bit;

signal OVERFLOW_CONTROL_AUX : bit;

--signal DECODING_UNDERFLOW_DELAY : bit;

begin

STATES : process (WAITN, START_C, START_D, THRESHOLD_LEVEL, CURRENT_STATE, FINISHED_C, FINISHED_D, C_DATA_VALID, DECODING_UNDERFLOW_AUX, DECODING_OVERFLOW_AUX, DECODING_READ_ADDRESS, DECODING_WRITE_ADDRESS, BUS_ACKNOWLEDGE)

begin

case CURRENT_STATE is

        when "0000" =>  -- state 0 buffer inactive. Two modes: test mode and decompression mode

                if (START_D = '0') then

                        NEXT_STATE <= "0001";

                elsif (START_C = '0') then

                        NEXT_STATE <= "1001";

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

            BUS_ACKNOWLEDGE_INT <= '0';

                DECODING_UNDERFLOW_INT <= '0';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

                CLEAR_COUNTERS <= '1'; -- read and write counters are at 0

         when "0001" =>  -- request data ( request the bus )

     if (FINISHED_D = '0' and BUS_ACKNOWLEDGE = '0' and WAITN = '1') then --simultanenously

                         NEXT_STATE <= "0101"; -- wait for a bus acknowledge before you finish

     elsif (FINISHED_D = '0') then -- if finish when requesting the bus

                         NEXT_STATE <= "0111"; -- wait for a bus acknowledge before you finish

                elsif (BUS_ACKNOWLEDGE = '0') then

                        NEXT_STATE <= "0010"; -- start writting data to the buffer

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '0';

                FINISH <= '1';

          CLEAR_COUNTERS <= '1';

         when "0010" =>    -- state 2 writing to the buffer

                if (FINISHED_D = '0' and BUS_ACKNOWLEDGE = '0' and WAITN = '1') then --the decompression engine finishes

                        NEXT_STATE <= "0101"; -- end

                elsif (FINISHED_D = '0') then --the decompression engine finishes. so automatically ends no more data needed all lbock reconstructed

                        NEXT_STATE <= "0111"; -- wait for acknowledge

        --      elsif(BUS_ACKNOWLEDGE = '1' and WAITN = '1') then -- no more data available to write to the buffer block is inside. This is only valid if bus_acknowledge negated means finish

        --              NEXT_STATE <= "0100"; -- start only reading

                elsif (DECODING_WRITE_ADDRESS - DECODING_READ_ADDRESS > THRESHOLD_LEVEL) then --start reading from the buffer

                        NEXT_STATE <= "0011"; -- start reading data from the buffer

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '1';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '1';

                BUS_REQUEST_INT <= '0';

                FINISH <= '1';

            CLEAR_COUNTERS <= '0';

         when "0011" =>    -- state 3 reading from the buffer and writting to it

     if (FINISHED_D = '0' and BUS_ACKNOWLEDGE = '0' and WAITN ='1') then --simultanenously

                         NEXT_STATE <= "0101"; -- wait for a bus acknowledge before you finish

                elsif (FINISHED_D = '0') then --the decompression engine finishes. so automatically ends no more data needed all lbock reconstructed

                        NEXT_STATE <= "0111"; -- wait for acknowledge

        --      elsif (BUS_ACKNOWLEDGE='1' and WAITN = '1')  then --stop writting to the buffer process terminates. This is only valid if bus_acknowledge negated means finish

        --              NEXT_STATE <= "0100"; -- only reading data from the buffer

        --      elsif ( DECODING_OVERFLOW_AUX = '0' or DECODING_WRITE_ADDRESS(8 downto 1) = "00111111") then

     elsif (DECODING_OVERFLOW_AUX = '0') then

                        NEXT_STATE <= "0110"; -- wait 

                elsif (DECODING_UNDERFLOW_AUX = '1') then -- only writting to the buffer. underflow can happen with wait states

                        NEXT_STATE <= "0010";

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '1';

                ENABLE_WRITE_INT <= '1';

                BUS_REQUEST_INT <= '0';

                FINISH <= '1';

        CLEAR_COUNTERS <= '0';

   -- this state is currently not reachable 

         when "0100" =>    -- state 4 reading from the buffer. In only reading never request more data

     if (FINISHED_D = '0' and BUS_ACKNOWLEDGE = '0' and WAITN = '1') then --simultanenously

                         NEXT_STATE <= "0101"; -- wait for a bus acknowledge before you finish

                elsif (FINISHED_D = '0') then --the decompression engine finishes. so automatically ends no more data needed all lbock reconstructed

                        NEXT_STATE <= "0111"; -- wait for acknowledge   

--              elsif (DECODING_UNDERFLOW_AUX = '1') then -- only writting to the buffer

--                      NEXT_STATE <= "0010";

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

        BUS_ACKNOWLEDGE_INT <= '0';

                ENABLE_READ_INT <= '1';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

            CLEAR_COUNTERS <= '0';

         when "0101" =>    -- signal finish

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '0';

                NEXT_STATE <= "0000"; -- end

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '0';

                CLEAR_COUNTERS <= '0';

        when "0110" =>    -- state 6 reading from the buffer. overflow more data needed

    if (FINISHED_D = '0') then --simultanenously

                         NEXT_STATE <= "0101"; -- wait for a bus acknowledge before you finish

                elsif (DECODING_UNDERFLOW_AUX = '1') then -- we have exahusted the compressed data request more

                        NEXT_STATE <= "0001"; -- request bus

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '1';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

            CLEAR_COUNTERS <= '0';

         when "0111" =>  -- request data ( request the bus ) waiting for the acknowlecge before finishing directly

                if (BUS_ACKNOWLEDGE = '0' and WAITN = '1') then

                        NEXT_STATE <= "0101"; -- finish directly

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '0';

                FINISH <= '1';

          CLEAR_COUNTERS <= '1';

         when "1001" =>  -- waiting for data in test mode 

                if (C_DATA_VALID = '0') then

                        NEXT_STATE <= "1010"; -- start writting data to the buffer

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

            CLEAR_COUNTERS <= '1';

        when "1010" =>    -- state 2 writing to the buffer

                if (FINISHED_C = '0') then -- no more data available to write to the buffer the whole block is inside finish

                        NEXT_STATE <= "1100"; -- start only reading

                elsif (C_DATA_VALID = '1') then

                        NEXT_STATE <= "1110"; -- wait 

                elsif (DECODING_WRITE_ADDRESS - DECODING_READ_ADDRESS > "0000000010") then --start reading from the buffer

                        NEXT_STATE <= "1011"; -- start reading data from the buffer

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '1';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '1';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

        CLEAR_COUNTERS <= '0';

   when "1011" =>    -- state 3 reading from the buffer and writting to it

                if (FINISHED_C ='0')  then --stop writting to the buffer process terminates

                        NEXT_STATE <= "1100"; -- only reading data from the buffer

                elsif (C_DATA_VALID = '1') then

                        NEXT_STATE <= "1110"; -- wait 

                elsif (DECODING_UNDERFLOW_AUX = '1') then -- only writting to the buffer

                        NEXT_STATE <= "1010";

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '1';

                ENABLE_WRITE_INT <= '1';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

        CLEAR_COUNTERS <= '0';

   when "1110" =>    -- wait state. state reading from the buffer but waiting to write more data

                if (FINISHED_C ='0')  then --stop writting to the buffer process terminates

                        NEXT_STATE <= "1100"; -- only reading data from the buffer      

        elsif(C_DATA_VALID = '0' and DECODING_UNDERFLOW_AUX = '1') then -- data available write but do not read with underflow

                        NEXT_STATE <= "1010"; --  write

                elsif (DECODING_UNDERFLOW_AUX = '1') then -- total wait do not read or write

                        NEXT_STATE <= "1111"; -- total wait do not read or write

                elsif(C_DATA_VALID = '0') then -- do not read or write

                        NEXT_STATE <= "1011"; -- read and write

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '1';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

        CLEAR_COUNTERS <= '0';

   when "1100" =>    -- state 4 reading from the buffer. In only reading never request more data

                if (FINISHED_D = '0') then --the decompression engine finishes

                        NEXT_STATE <= "1101"; -- end  

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '0';

        BUS_ACKNOWLEDGE_INT <= '0';

                ENABLE_READ_INT <= '1';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

        CLEAR_COUNTERS <= '0';

    when "1101" =>    -- signal finish

                DECODING_UNDERFLOW_INT <= '0';

                BUS_ACKNOWLEDGE_INT <= '0';

                NEXT_STATE <= "0000"; -- end

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '0';

                CLEAR_COUNTERS <= '0';

        when "1111" =>    -- wait state. state reading from the buffer but waiting to write more data

                if (FINISHED_C ='0')  then --stop writting to the buffer process terminates

                        NEXT_STATE <= "1100"; -- only reading data from the buffer      

                elsif(C_DATA_VALID = '0') then -- do not read or write

                        NEXT_STATE <= "1010"; -- write to the buffer

                else

                        NEXT_STATE <= CURRENT_STATE;

                end if;

                DECODING_UNDERFLOW_INT <= '1';

                BUS_ACKNOWLEDGE_INT <= '1';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

        CLEAR_COUNTERS <= '0';

         when others =>

                NEXT_STATE <= "0000";

                BUS_ACKNOWLEDGE_INT <= '0';

                DECODING_UNDERFLOW_INT <= '0';

                ENABLE_READ_INT <= '0';

                ENABLE_WRITE_INT <= '0';

                BUS_REQUEST_INT <= '1';

                FINISH <= '1';

                CLEAR_COUNTERS <= '1';

end  case;

end process STATES;

--DECODING_OVERFLOW_AUX <= '0' when ((DECODING_READ_ADDRESS(8 downto 1) = DECODING_WRITE_ADDRESS(8 downto 1) + "00000001") and (BUS_ACKNOWLEDGE_INT = '1')) else '1'; -- decoding overflow goes out of the chip is active with zero if bus_akcnowledge 1 then all the data is inside never generate overflow

DECODING_OVERFLOW_AUX <= '0' when (CURRENT_STATE(3) = '0' and (DECODING_WRITE_ADDRESS(9 downto 1) = "001000000") and (BUS_ACKNOWLEDGE_INT = '1')) else '1'; -- decoding overflow goes out of the chip is active with zero if bus_akcnowledge 1 then all the data is inside never generate overflow

DECODING_UNDERFLOW_AUX <= '1' when ((DECODING_WRITE_ADDRESS(9 downto 1) = DECODING_READ_ADDRESS(9 downto 1)) and (BUS_ACKNOWLEDGE_INT = '1') and (UNDERFLOW = '0')) else '0'; --the engine must requests data. In this case engine could request data beucase it is detected one cycle earlier

ENABLE_READ <= ENABLE_READ_INT and not(DECODING_UNDERFLOW_AUX); -- if decoding underflow disable the read counter 

ENABLE_WRITE <= ENABLE_WRITE_INT and DECODING_OVERFLOW_AUX; -- if overflow disable writting inmediatly

BUS_REQUEST <= BUS_REQUEST_INT or not(DECODING_OVERFLOW_AUX);

FLIP_FLOPS2 : process(CLK, CLEAR)

begin

if (CLEAR = '0') then

        OVERFLOW_CONTROL_AUX <= '0'; --state 0

elsif ((CLK'event) and (CLK='1')) then

     if (FORCE_STOP = '0') then

                                OVERFLOW_CONTROL_AUX <= '0'; --state 0

     elsif (CURRENT_STATE(3) = '1' and (DECODING_READ_ADDRESS = DECODING_WRITE_ADDRESS + "110000000")) then

                                OVERFLOW_CONTROL_AUX <= '1';

          elsif (DECODING_WRITE_ADDRESS = DECODING_READ_ADDRESS + "000000010" and WAITN = '1') then-- buffer empty    

                          OVERFLOW_CONTROL_AUX <= '0';

    else

                  OVERFLOW_CONTROL_AUX <= OVERFLOW_CONTROL_AUX;

                end if;

end if;

end process FLIP_FLOPS2;

OVERFLOW_CONTROL <= OVERFLOW_CONTROL_AUX;

FLIP_FLOPS : process(CLK, CLEAR)

begin

if (CLEAR = '0') then

        CURRENT_STATE <= "0000"; --state 0

elsif ((CLK'event) and (CLK='1')) then

  if (FORCE_STOP = '0') then

                CURRENT_STATE <= "0000";

  else

                CURRENT_STATE <= NEXT_STATE;

  end if;

end if;

end process FLIP_FLOPS;

--DELAY_UNDERFLOW : process(CLK, CLEAR, DECODING_UNDERFLOW_DELAY)

--begin 

--if (CLEAR = '0') then

--      DECODING_UNDERFLOW <= '0';

--elsif ((CLK'event) and (CLK='1')) then

--      DECODING_UNDERFLOW <= DECODING_UNDERFLOW_DELAY;

--end if;

--end process DELAY_UNDERFLOW;

DECODING_UNDERFLOW <= DECODING_UNDERFLOW_AUX or DECODING_UNDERFLOW_INT; -- never signal underflow if bus_acknowledge has gone to 1 it means that all the compressed data has been fed to the buffer. It has to terminate

end STRUCTURAL;