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-- $Id: rbd_bram.vhd 427 2011-11-19 21:04:11Z mueller $

--

-- Copyright 2010-2011 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:    rbd_bram - syn

-- Description:    rbus dev: rbus bram test target

--

-- Dependencies:   memlib/ram_1swsr_wfirst_gen

--

-- Test bench:     rlink/tb/tb_rlink_tba_ttcombo

--

-- Target Devices: generic

-- Tool versions:  xst 12.1, 13.1; ghdl 0.29

--

-- Synthesized (xst):

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

-- 2010-12-26   349 12.1    M53d xc3s1000-4    23   61    -   34 s  6.3

--

-- Revision History: 

-- Date         Rev Version  Comment

-- 2011-11-19   427   1.0.3  now numeric_std clean

-- 2010-12-31   352   1.0.2  simplify irb_ack logic

-- 2010-12-29   351   1.0.1  default addr 1111001x->1111010x

-- 2010-12-26   349   1.0    Initial version 

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

--

-- rbus registers:

--

-- Address   Bits Name        r/w/f  Function

-- bbbbbbb0       cntl        r/w/-  Control register

--          15:10   nbusy     r/w/-    busy cycles

--           9:00   addr      r/w/-    bram address (will auto-increment)

-- bbbbbbb1 15:00 data        r/w/-  Data register (read/write to bram via addr)

--

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.slvtypes.all;

use work.memlib.all;

use work.rblib.all;

entity rbd_bram is                      -- rbus dev: rbus bram test target

                                        -- complete rrirp_aif interface

  generic (

    RB_ADDR : slv8 := slv(to_unsigned(2#11110100#,8)));

  port (

    CLK  : in slbit;                    -- clock

    RESET : in slbit;                   -- reset

    RB_MREQ : in rb_mreq_type;          -- rbus: request

    RB_SRES : out rb_sres_type          -- rbus: response

  );

end entity rbd_bram;

architecture syn of rbd_bram is

  constant rbaddr_cntl : slv1 := "0";   -- cntl address offset

  constant rbaddr_data : slv1 := "1";   -- data address offset

  subtype  cntl_rbf_nbusy   is integer range 15 downto 10;

  subtype  cntl_rbf_addr    is integer range  9 downto  0;

  type regs_type is record              -- state registers

    rbsel : slbit;                      -- rbus select

    addr : slv10;                       -- addr register

    nbusy : slv6;                       -- nbusy setting

    cntbusy : slv6;                     -- busy timer

  end record regs_type;

  constant regs_init : regs_type := (

    '0',                                -- rbsel

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

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

    (others=>'0')                       -- cntbusy

  );

  signal R_REGS : regs_type := regs_init;

  signal N_REGS : regs_type := regs_init;

  signal BRAM_EN : slbit := '0';

  signal BRAM_WE : slbit := '0';

  signal BRAM_DO : slv16 := (others=>'0');

begin

  BRAM : ram_1swsr_wfirst_gen

    generic map (

      AWIDTH => 10,

      DWIDTH => 16)

    port map (

      CLK   => CLK,

      EN    => BRAM_EN,

      WE    => BRAM_WE,

      ADDR  => R_REGS.addr,

      DI    => RB_MREQ.din,

      DO    => BRAM_DO

    );

  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, RB_MREQ, BRAM_DO)

    variable r : regs_type := regs_init;

    variable n : regs_type := regs_init;

    variable irb_ack  : slbit := '0';

    variable irb_busy : slbit := '0';

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

    variable irbena : slbit := '0';

    variable isbusy : slbit := '0';

    variable ibramen : slbit := '0';

    variable ibramwe : slbit := '0';

  begin

    r := R_REGS;

    n := R_REGS;

    irb_ack  := '0';

    irb_busy := '0';

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

    irbena  := RB_MREQ.re or RB_MREQ.we;

    isbusy := '0';

    if unsigned(r.cntbusy) /= 0 then

      isbusy := '1';

    end if;

    ibramen := '0';

    ibramwe := '0';

    -- rbus address decoder

    n.rbsel := '0';

    if RB_MREQ.aval='1' and RB_MREQ.addr(7 downto 1)=RB_ADDR(7 downto 1) then

      n.rbsel := '1';

      ibramen := '1';

      if irbena = '0' then              -- addr valid and selected, but no req

        n.cntbusy := r.nbusy;             -- preset busy timer

      end if;

    end if;

    -- rbus transactions

    if r.rbsel = '1' then

      if irbena = '1' then              -- if request active

        if unsigned(r.cntbusy) /= 0 then  -- if busy timer > 0

          n.cntbusy := slv(unsigned(r.cntbusy) - 1); -- decrement busy timer

        end if;

      end if;

      irb_ack := irbena;                  -- ack all accesses

      case RB_MREQ.addr(0 downto 0) is

        when rbaddr_cntl =>

          if RB_MREQ.we = '1' then

            n.nbusy  := RB_MREQ.din(cntl_rbf_nbusy);

            n.addr   := RB_MREQ.din(cntl_rbf_addr);

          end if;

        when rbaddr_data =>

          irb_busy := irbena and isbusy;

          if isbusy = '0' then

            if RB_MREQ.we = '1' then

              ibramwe := '1';

            end if;

            if irbena = '1' then

              n.addr := slv(unsigned(r.addr) + 1);

            end if;

          end if;

        when others => null;

      end case;

    end if;

    -- rbus output driver

    if r.rbsel = '1' then

      case RB_MREQ.addr(0 downto 0) is

        when rbaddr_cntl =>

          irb_dout(cntl_rbf_nbusy) := r.nbusy;

          irb_dout(cntl_rbf_addr)  := r.addr;

        when rbaddr_data =>

          irb_dout := BRAM_DO;

        when others => null;

      end case;

    end if;

    N_REGS <= n;

    BRAM_EN <= ibramen;

    BRAM_WE <= ibramwe;

    RB_SRES.dout <= irb_dout;

    RB_SRES.ack  <= irb_ack;

    RB_SRES.err  <= '0';

    RB_SRES.busy <= irb_busy;

  end process proc_next;

end syn;