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

-- Title      :  Rx Controller

-- Project    :  HDLC controller

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

-- File        : Rxcont.vhd

-- Author      : Jamil Khatib  (khatib@ieee.org)

-- Organization: OpenIPCore Project

-- Created     : 2000/12/30

-- Last update: 2001/04/27

-- Platform    : 

-- Simulators  : Modelsim 5.3XE/Windows98

-- Synthesizers: 

-- Target      : 

-- Dependency  : ieee.std_logic_1164

--

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

-- Description:  receive Controller

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

-- Copyright (c) 2000 Jamil Khatib

-- 

-- This VHDL design file is an open design; you can redistribute it and/or

-- modify it and/or implement it after contacting the author

-- You can check the draft license at

-- http://www.opencores.org/OIPC/license.shtml

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

-- Revisions  :

-- Revision Number :   1

-- Version         :   0.1

-- Date            :   30 Dec 2000

-- Modifier        :   Jamil Khatib (khatib@ieee.org)

-- Desccription    :   Created

-- ToOptimize      :

-- Bugs            :   

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

-- Revisions  :

-- Revision Number :   2

-- Version         :   0.2

-- Date            :   27 April 2001

-- Modifier        :   Jamil Khatib (khatib@ieee.org)

-- Desccription    :   Enable and Available Bugs fixed

-- ToOptimize      :

-- Bugs            :   

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

library ieee;

use ieee.std_logic_1164.all;

entity rxcont_ent is

  port (

    RxClk        : in  std_logic;       -- Rx Clcok

    rst          : in  std_logic;       -- system Reset

    RxEn         : in  std_logic;       -- Rx Enable

    AbortedFrame : out std_logic;       -- Aborted frame

    Abort        : in  std_logic;       -- Abort detected

    FlagDetect   : in  std_logic;       -- Flag Detect

    ValidFrame   : out std_logic;       -- Valid Frame

    FrameError   : out std_logic;       -- Frame Error (Indicates error in the

                                        -- next byte at the backend

    aval         : in  std_logic;       -- Can accept more data

    initzero     : out std_logic;       -- init Zero detect block

    enable       : out std_logic);      -- Enable

end rxcont_ent;

architecture rxcont_beh of rxcont_ent is

--  signal validFrame_i : std_logic;    -- Internal Valid Frame signal

begin  -- rxcont_beh

-- purpose: Enable controller

-- type   : sequential

-- inputs : Rxclk, rst

-- outputs: 

  enable_proc               : process (Rxclk, rst)

    variable counter        : integer range 0 to 7;  -- Counter

    variable FlagCounter    : integer range 0 to 7;  -- Flag bits counter

    variable FrameStatus    : std_logic;  -- Frame Status

    variable FlagInit       : std_logic;  -- Init flag counter

    variable FrameStatusReg : std_logic_vector(7 downto 0);

                                        -- Delay for Frame Status

  begin  -- process enable_proc

    if rst = '0' then                   -- asynchronous reset (active low)

      enable         <= '0';

      FrameStatus    := '0';

      ValidFrame     <= '0';

      AbortedFrame   <= '0';

      Counter        := 0;

      FlagInit       := '0';

      initzero       <= '0';

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

                FrameError <= '0';

          FlagCounter := 0;

    elsif Rxclk'event and Rxclk = '1' then  -- rising clock edge

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

-- This is the Valid frame machine

      if FlagDetect = '1' then

        FlagInit     := '1';

        FrameStatus  := '0';

        FlagCounter  := 0;

        AbortedFrame <= '0';

      end if;

      if FlagInit = '1' then

        if FlagCounter = 7 then

          FrameStatus := '1';

          FlagCounter := 0;

          initzero    <= '1';

          FlagInit    := '0';

        else

          FlagCounter := FlagCounter + 1;

          initzero    <= '0';

        end if;

      else

        initzero      <= '0';

      end if;

      if Abort = '1' then

        FrameStatus  := '0';

        AbortedFrame <= '1';

      end if;

      ValidFrame     <= FrameStatusReg(0);

      FrameStatusReg(7 downto 0) := FrameStatus & FrameStatusReg(7 downto 1);

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

-- This is the enable machine

      if RxEn = '1' then

        if FrameStatus = '1' then

          if aval = '1' then

            enable     <= '1';

            Counter    := 0;

            FrameError <= '0';

          else

            if counter = 5 then

              enable <= '0';

              counter := 0;

              FrameError <= '1';

            else

              enable <= '1';

              Counter    := Counter +1;

              FrameError <= '0';

            end if;  -- counter

          end if;  -- aval

        else

          FrameError <= '0';

          enable     <= '0';

--        Counter := 0;

        end if;  -- validframe

      else

        FrameError <= '0';

        enable     <= '0';

--      Counter := 0;

      end if;  -- rxen

    end if;  -- clock

  end process enable_proc;

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

end rxcont_beh;