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-- $Id: ibdr_sdreg.vhd 335 2010-10-24 22:24:23Z mueller $

--

-- Copyright 2007-2010 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:    ibdr_sdreg - syn

-- Description:    ibus dev(rem): Switch/Display register

--

-- Dependencies:   -

-- Test bench:     -

-- Target Devices: generic

-- Tool versions:  xst 8.1, 8.2, 9.1, 9.2, 10.1, 12.1; ghdl 0.18-0.29

--

-- Synthesized (xst):

-- Date         Rev  ise         Target      flop lutl lutm slic t peri

-- 2010-10-17   333  12.1    M53 xc3s1000-4    34   40    0   30 s  4.0

-- 2009-07-11   232  10.1.03 K39 xc3s1000-4    32   39    0   29 s  2.5

--

-- Revision History: 

-- Date         Rev Version  Comment

-- 2010-10-17   333   1.2    use ibus V2 interface

-- 2010-06-11   303   1.1    use IB_MREQ.racc instead of RRI_REQ

-- 2008-08-22   161   1.0.4  use iblib

-- 2008-04-18   136   1.0.3  use RESET. Switch/Display not cleared by console

--                           reset or reset instruction, only by cpu_reset

-- 2008-01-20   112   1.0.2  use BRESET

-- 2008-01-05   110   1.0.1  rename IB_MREQ(ena->req) SRES(sel->ack, hold->busy)

--                           reorganize code, all in state_type/proc_next

-- 2007-12-31   108   1.0    Initial version 

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use work.slvtypes.all;

use work.iblib.all;

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

entity ibdr_sdreg is                    -- ibus dev(rem): Switch/Display regs

                                        -- fixed address: 177570

  port (

    CLK : in slbit;                     -- clock

    RESET : in slbit;                   -- reset

    IB_MREQ : in ib_mreq_type;          -- ibus request

    IB_SRES : out ib_sres_type;         -- ibus response

    DISPREG : out slv16                 -- display register

  );

end ibdr_sdreg;

architecture syn of ibdr_sdreg is

  constant ibaddr_sdreg : slv16 := conv_std_logic_vector(8#177570#,16);

  type regs_type is record              -- state registers

    ibsel : slbit;                      -- ibus select

    sreg : slv16;                       -- switch register

    dreg : slv16;                       -- display register

  end record regs_type;

  constant regs_init : regs_type := (

    '0',                                -- ibsel

    (others=>'0'),                      -- sreg

    (others=>'0')                       -- dreg

  );

  signal R_REGS : regs_type := regs_init;

  signal N_REGS : regs_type := regs_init;

begin

  proc_regs: process (CLK)

  begin

    if CLK'event and CLK='1' 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, IB_MREQ)

    variable r : regs_type := regs_init;

    variable n : regs_type := regs_init;

    variable idout : slv16 := (others=>'0');

    variable ibreq : slbit := '0';

  begin

    r := R_REGS;

    n := R_REGS;

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

    ibreq := IB_MREQ.re or IB_MREQ.we;

    -- ibus address decoder

    n.ibsel := '0';

    if IB_MREQ.aval='1' and

       IB_MREQ.addr=ibaddr_sdreg(12 downto 1) then

      n.ibsel := '1';

    end if;

    -- ibus output driver

    if r.ibsel = '1' then

      if IB_MREQ.racc = '0' then

        idout := r.sreg;             -- cpu will read switch register

      else

        idout := r.dreg;             -- rri will read display register

      end if;

    end if;

    -- ibus write transactions

    if r.ibsel='1' and IB_MREQ.we='1' then

      if IB_MREQ.racc = '0' then     -- cpu will write display register

        if IB_MREQ.be1 = '1' then

          n.dreg(ibf_byte1) := IB_MREQ.din(ibf_byte1);

        end if;

        if IB_MREQ.be0 = '1' then

          n.dreg(ibf_byte0) := IB_MREQ.din(ibf_byte0);

        end if;

      else                          -- rri will write switch register

        n.sreg := IB_MREQ.din;        -- byte write not supported

      end if;

    end if;

    N_REGS <= n;

    IB_SRES.dout <= idout;

    IB_SRES.ack  <= r.ibsel and ibreq;

    IB_SRES.busy <= '0';

    DISPREG <= r.dreg;

  end process proc_next;

end syn;