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-- $Id: s3_sram_memctl.vhd 314 2010-07-09 17:38:41Z 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:    s3_sram_memctl - syn

-- Description:    s3board: SRAM driver

--

-- Dependencies:   vlib/xlib/iob_reg_o

--                 vlib/xlib/iob_reg_o_gen

--                 vlib/xlib/iob_reg_io_gen

-- Test bench:     tb/tb_s3_sram_memctl

--                 fw_gen/tst_sram/s3board/tb/tb_tst_sram_s3

-- Target Devices: generic

-- Tool versions:  xst 8.1, 8.2, 9.1, 9.2; ghdl 0.18-0.25

--

-- Synthesized (xst):

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

-- 2010-05-23   293  11.4   L68  xc3s1000-4     7   22    0   14 s  8.5

-- 2008-02-16   116  8.2.03 I34  xc3s1000-4     5   30    0   17 s  7.0

--

-- Revision History: 

-- Date         Rev Version  Comment

-- 2010-06-03   299   1.0.5  add "KEEP" for data iob;

-- 2010-05-16   291   1.0.4  rename memctl_s3sram -> s3_sram_memctl

-- 2008-02-17   117   1.0.3  use req,we rather req_r,req_w interface

-- 2008-01-20   113   1.0.2  rename memdrv -> memctl_s3sram

-- 2007-12-15   101   1.0.1  use _N for active low; get ce/we clocking right

-- 2007-12-08   100   1.0    Initial version 

--

-- Timing of some signals:

--

-- single read request:

-- 

-- state       |_idle  |_read  |_idle  |

-- 

-- CLK       __|^^^|___|^^^|___|^^^|___|^

-- 

-- REQ       _______|^^^^^|______________

-- WE        ____________________________

-- 

-- IOB_CE    __________|^^^^^^^|_________

-- IOB_OE    __________|^^^^^^^|_________

-- 

-- DO        oooooooooooooooooo|ddddddd|d

-- BUSY      ____________________________

-- ACK_R     __________________|^^^^^^^|_

-- 

-- single write request:

-- 

-- state       |_idle  |_write1|_write2|_idle  |

-- 

-- CLK       __|^^^|___|^^^|___|^^^|___|^^^|___|^

-- 

-- REQ       _______|^^^^^|______________

-- WE        _______|^^^^^|______________

-- 

-- IOB_CE    __________|^^^^^^^^^^^^^^^|_________

-- IOB_BE    __________|^^^^^^^^^^^^^^^|_________

-- IOB_OE    ____________________________________

-- IOB_WE    ______________|^^^^^^^|_____________

-- 

-- BUSY      __________|^^^^^^^|_________________

-- ACK_W     __________________|^^^^^^^|_________

-- 

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use work.slvtypes.all;

use work.xlib.all;

entity s3_sram_memctl is                -- SRAM driver for S3BOARD

  port (

    CLK : in slbit;                     -- clock

    RESET : in slbit;                   -- reset

    REQ   : in slbit;                   -- request

    WE    : in slbit;                   -- write enable

    BUSY : out slbit;                   -- controller busy

    ACK_R : out slbit;                  -- acknowledge read

    ACK_W : out slbit;                  -- acknowledge write

    ACT_R : out slbit;                  -- signal active read

    ACT_W : out slbit;                  -- signal active write

    ADDR : in slv18;                    -- address

    BE : in slv4;                       -- byte enable

    DI : in slv32;                      -- data in  (memory view)

    DO : out slv32;                     -- data out (memory view)

    O_MEM_CE_N : out slv2;              -- sram: chip enables  (act.low)

    O_MEM_BE_N : out slv4;              -- sram: byte enables  (act.low)

    O_MEM_WE_N : out slbit;             -- sram: write enable  (act.low)

    O_MEM_OE_N : out slbit;             -- sram: output enable (act.low)

    O_MEM_ADDR  : out slv18;            -- sram: address lines

    IO_MEM_DATA : inout slv32           -- sram: data lines

  );

end s3_sram_memctl;

architecture syn of s3_sram_memctl is

  type state_type is (

    s_idle,                             -- s_idle: wait for req

    s_read,                             -- s_read: read cycle

    s_write1,                           -- s_write1: write cycle, 1st half

    s_write2,                           -- s_write2: write cycle, 2nd half

    s_bta_r2w,                          -- s_bta_r2w: bus turn around: r->w

    s_bta_w2r                           -- s_bta_w2r: bus turn around: w->r

  );

  type regs_type is record

    state : state_type;                 -- state

    ackr : slbit;                       -- signal ack_r

  end record regs_type;

  constant regs_init : regs_type := (

    s_idle,

    '0'                                 -- ackr

  );

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

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

  signal CLK_180  : slbit := '0';

  signal MEM_CE_N : slv2 := "00";

  signal MEM_BE_N : slv4 := "0000";

  signal MEM_WE_N : slbit := '0';

  signal MEM_OE_N : slbit := '0';

  signal ADDR_CE  : slbit := '0';

  signal DATA_CEI : slbit := '0';

  signal DATA_CEO : slbit := '0';

  signal DATA_OE  : slbit := '0';

begin

  CLK_180 <= not CLK;

  IOB_MEM_CE : iob_reg_o_gen

    generic map (

      DWIDTH => 2,

      INIT   => '1')

    port map (

      CLK => CLK,

      CE  => '1',

      DO  => MEM_CE_N,

      PAD => O_MEM_CE_N

    );

  IOB_MEM_BE : iob_reg_o_gen

    generic map (

      DWIDTH => 4,

      INIT   => '1')

    port map (

      CLK => CLK,

      CE  => ADDR_CE,

      DO  => MEM_BE_N,

      PAD => O_MEM_BE_N

    );

  IOB_MEM_WE : iob_reg_o

    generic map (

      INIT   => '1')

    port map (

      CLK => CLK_180,

      CE  => '1',

      DO  => MEM_WE_N,

      PAD => O_MEM_WE_N

    );

  IOB_MEM_OE : iob_reg_o

    generic map (

      INIT   => '1')

    port map (

      CLK => CLK,

      CE  => '1',

      DO  => MEM_OE_N,

      PAD => O_MEM_OE_N

    );

  IOB_MEM_ADDR : iob_reg_o_gen

    generic map (

      DWIDTH => 18)

    port map (

      CLK => CLK,

      CE  => ADDR_CE,

      DO  => ADDR,

      PAD => O_MEM_ADDR

    );

  IOB_MEM_DATA : iob_reg_io_gen

    generic map (

      DWIDTH => 32,

      PULL   => "KEEP")

    port map (

      CLK => CLK,

      CEI => DATA_CEI,

      CEO => DATA_CEO,

      OE  => DATA_OE,

      DI  => DO,

      DO  => DI,

      PAD => IO_MEM_DATA

    );

  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, REQ, WE, BE)

    variable r : regs_type := regs_init;

    variable n : regs_type := regs_init;

    variable ibusy : slbit := '0';

    variable iackw : slbit := '0';

    variable iactr : slbit := '0';

    variable iactw : slbit := '0';

    variable imem_ce : slv2 := "00";

    variable imem_be : slv4 := "0000";

    variable imem_we : slbit := '0';

    variable imem_oe : slbit := '0';

    variable iaddr_ce  : slbit := '0';

    variable idata_cei : slbit := '0';

    variable idata_ceo : slbit := '0';

    variable idata_oe  : slbit := '0';

  begin

    r := R_REGS;

    n := R_REGS;

    n.ackr := '0';

    ibusy := '0';

    iackw := '0';

    iactr := '0';

    iactw := '0';

    imem_ce := "00";

    imem_be := "1111";

    imem_we := '0';

    imem_oe := '0';

    iaddr_ce  := '0';

    idata_cei := '0';

    idata_ceo := '0';

    idata_oe  := '0';

    case r.state is

      when s_idle =>                    -- s_idle: wait for req

        if REQ = '1' then                 -- if IO requested

          if WE = '0' then                  -- if READ requested

            iaddr_ce := '1';                  -- latch address and be's

            imem_ce  := "11";                 -- ce SRAM next cycle

            imem_oe  := '1';                  -- oe SRAM next cycle

            n.state := s_read;                -- next: read

          else                              -- if WRITE requested

            iaddr_ce  := '1';                 -- latch address and be's

            idata_ceo := '1';                 -- latch output data

            idata_oe  := '1';                 -- oe FPGA next cycle

            imem_ce   := "11";                -- ce SRAM next cycle

            imem_be   := BE;                  -- use request BE's

            n.state := s_write1;              -- next: write 1st part

          end if;

        end if;

      when s_read =>                    -- s_read: read cycle

        idata_cei := '1';                 -- latch input data

        iactr := '1';                     -- signal mem read

        n.ackr := '1';                    -- ACK_R next cycle

        if REQ = '1' then                 -- if IO requested

          if WE = '0' then                  -- if READ requested

            iaddr_ce := '1';                  -- latch address and be's

            imem_ce  := "11";                 -- ce SRAM next cycle

            imem_oe  := '1';                  -- oe SRAM next cycle

            n.state := s_read;                -- next: continue read

          else                              -- if WRITE requested

            iaddr_ce  := '1';                 -- latch address and be's

            idata_ceo := '1';                 -- latch output data

            imem_be   := BE;                  -- use request BE's

            n.state := s_bta_r2w;             -- next: bus turn around cycle

          end if;

        else

          n.state := s_idle;              -- next: idle if nothing to do

        end if;

      when s_write1 =>                  -- s_write1: write cycle, 1st half

        ibusy := '1';                     -- signal busy, unable to handle req

        iactw := '1';                     -- signal mem write

        idata_oe := '1';                  -- oe FPGA next cycle

        imem_ce  := "11";                 -- ce SRAM next cycle

        imem_we  := '1';                  -- we SRAM next shifted cycle

        n.state := s_write2;              -- next: write cycle, 2nd half

      when s_write2 =>                  -- s_write2: write cycle, 2nd half

        iactw := '1';                     -- signal mem write

        iackw := '1';                     -- signal write acknowledge

        idata_cei := '1';                 -- latch input data (from SRAM)

        if REQ = '1' then                 -- if IO requested

          if WE = '1' then                  -- if WRITE requested

            iaddr_ce  := '1';                 -- latch address and be's

            idata_ceo := '1';                 -- latch output data

            idata_oe  := '1';                 -- oe FPGA next cycle

            imem_ce   := "11";                -- ce SRAM next cycle

            imem_be   := BE;                  -- use request BE's

            n.state := s_write1;              -- next: continue read

          else                              -- if READ requested

            iaddr_ce := '1';                  -- latch address and be's

            n.state := s_bta_w2r;             -- next: bus turn around cycle

          end if;

        else

          n.state := s_idle;              -- next: idle if nothing to do

        end if;

      when s_bta_r2w =>                 -- s_bta_r2w: bus turn around: r->w

        ibusy := '1';                     -- signal busy, unable to handle req

        iactw := '1';                     -- signal mem write

        imem_ce  := "11";                 -- ce SRAM next cycle

        idata_oe := '1';                  -- oe FPGA next cycle

        n.state := s_write1;              -- next: start write

      when s_bta_w2r =>                 -- s_bta_w2r: bus turn around: w->r

        ibusy := '1';                     -- signal busy, unable to handle req

        iactr := '1';                     -- signal mem read

        imem_ce := "11";                  -- ce SRAM next cycle

        imem_oe := '1';                   -- oe SRAM next cycle

        n.state := s_read;                -- next: start read

      when others => null;

    end case;

    N_REGS <= n;

    MEM_CE_N <= not imem_ce;

    MEM_WE_N <= not imem_we;

    MEM_BE_N <= not imem_be;

    MEM_OE_N <= not imem_oe;

    ADDR_CE  <= iaddr_ce;

    DATA_CEI <= idata_cei;

    DATA_CEO <= idata_ceo;

    DATA_OE  <= idata_oe;

    BUSY  <= ibusy;

    ACK_R <= r.ackr;

    ACK_W <= iackw;

    ACT_R <= iactr;

    ACT_W <= iactw;

  end process proc_next;

end syn;