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-- $Id: byte2word.vhd 432 2011-11-25 20:16:28Z mueller $

--

-- Copyright 2011- by Walter F.J. Mueller <W.F.J.Mueller@gsi.de>

--

-- This program is free software; you may redistribute and/or modify it under

-- the terms of the GNU General Public License as published by the Free

-- Software Foundation, either version 2, or at your option any later version.

--

-- This program 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 General Public License

-- for complete details.

--

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

-- Module Name:    byte2word - syn

-- Description:    2 byte -> 1 word stream converter

--

-- Dependencies:   -

-- Test bench:     -

-- Target Devices: generic

-- Tool versions:  xst 12.1; ghdl 0.29

--

-- Revision History: 

-- Date         Rev Version  Comment

-- 2011-11-21   432   1.0.1  now numeric_std clean

-- 2011-07-30   400   1.0    Initial version 

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.slvtypes.all;

entity byte2word is                     -- 2 byte -> 1 word stream converter

  port (

    CLK : in slbit;                     -- clock

    RESET : in slbit;                   -- reset

    DI : in slv8;                       -- input data (byte)

    ENA : in slbit;                     -- write enable

    BUSY : out slbit;                   -- write port hold    

    DO : out slv16;                     -- output data (word)

    VAL : out slbit;                    -- read valid

    HOLD : in slbit;                    -- read hold

    ODD : out slbit                     -- odd byte pending

  );

end byte2word;

architecture syn of byte2word is

  type state_type is (

    s_idle,

    s_vall,

    s_valw

  );

  type regs_type is record

    datl : slv8;                        -- lsb data

    dath : slv8;                        -- msb data

    state : state_type;                 -- state

  end record regs_type;

  constant regs_init : regs_type := (

    (others=>'0'),

    (others=>'0'),

    s_idle

  );

  signal R_REGS : regs_type := regs_init;  -- state registers

  signal N_REGS : regs_type := regs_init;  -- next value state regs

begin

  proc_regs: process (CLK)

  begin

    if rising_edge(CLK) then

      if RESET = '1' then

        R_REGS <= regs_init;

      else

        R_REGS <= N_REGS;

      end if;

    end if;

  end process proc_regs;

  proc_next: process (R_REGS, DI, ENA, HOLD)

    variable r : regs_type := regs_init;

    variable n : regs_type := regs_init;

    variable ival  : slbit := '0';

    variable ibusy : slbit := '0';

    variable iodd  : slbit := '0';

  begin

    r := R_REGS;

    n := R_REGS;

    ival  := '0';

    ibusy := '0';

    iodd  := '0';

    case r.state is

      when s_idle =>

        if ENA = '1' then

          n.datl := DI;

          n.state := s_vall;

        end if;

      when s_vall =>

        iodd := '1';

        if ENA = '1' then

          n.dath := DI;

          n.state := s_valw;

        end if;

      when s_valw =>

        ival := '1';

        if HOLD = '0' then

          if ENA = '1' then

            n.datl := DI;

            n.state := s_vall;

          else

            n.state := s_idle;

          end if;

        else

          ibusy := '1';

        end if;

      when others => null;

    end case;

    N_REGS <= n;

    DO   <= r.dath & r.datl;

    VAL  <= ival;

    BUSY <= ibusy;

    ODD  <= iodd;

  end process proc_next;

end syn;