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library IEEE, UNISIM;
use IEEE.std_logic_1164.all;
 
package sdram is
 
  -- SDRAM controller
  component sdramCntl
    generic(
      FREQ                 :     natural := 100_000;  -- operating frequency in KHz
      IN_PHASE             :     boolean := true;  -- SDRAM and controller work on same or opposite clock edge
      PIPE_EN              :     boolean := false;  -- if true, enable pipelined read operations
      MAX_NOP              :     natural := 10000;  -- number of NOPs before entering self-refresh
      MULTIPLE_ACTIVE_ROWS :     boolean := false;  -- if true, allow an active row in each bank
      DATA_WIDTH           :     natural := 16;  -- host & SDRAM data width
      NROWS                :     natural := 8192;  -- number of rows in SDRAM array
      NCOLS                :     natural := 512;  -- number of columns in SDRAM array
      HADDR_WIDTH          :     natural := 24;  -- host-side address width
      SADDR_WIDTH          :     natural := 13  -- SDRAM-side address width
      );
    port(
      -- host side
      clk                  : in  std_logic;  -- master clock
      lock                 : in  std_logic;  -- true if clock is stable
      rst                  : in  std_logic;  -- reset
      rd                   : in  std_logic;  -- initiate read operation
      wr                   : in  std_logic;  -- initiate write operation
      uds                  : in  std_logic;  -- upper byte data strobe
      lds                  : in  std_logic;  -- lower byte data strobe
      earlyOpBegun         : out std_logic;  -- read/write/self-refresh op has begun (async)
      opBegun              : out std_logic;  -- read/write/self-refresh op has begun (clocked)
      rdPending            : out std_logic;  -- true if read operation(s) are still in the pipeline
      done                 : out std_logic;  -- read or write operation is done
      rdDone               : out std_logic;  -- read operation is done and data is available
      hAddr                : in  std_logic_vector(HADDR_WIDTH-1 downto 0);  -- address from host to SDRAM
      hDIn                 : in  std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from host       to SDRAM
      hDOut                : out std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from SDRAM to host
      status               : out std_logic_vector(3 downto 0);  -- diagnostic status of the FSM         
      -- SDRAM side
      cke                  : out std_logic;  -- clock-enable to SDRAM
      ce_n                 : out std_logic;  -- chip-select to SDRAM
      ras_n                : out std_logic;  -- SDRAM row address strobe
      cas_n                : out std_logic;  -- SDRAM column address strobe
      we_n                 : out std_logic;  -- SDRAM write enable
      ba                   : out std_logic_vector(1 downto 0);  -- SDRAM bank address
      sAddr                : out std_logic_vector(SADDR_WIDTH-1 downto 0);  -- SDRAM row/column address
      sDIn                 : in  std_logic_vector(DATA_WIDTH-1 downto 0);  -- data to SDRAM
      sDOut                : out std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from SDRAM
      sDOutEn              : out std_logic;  -- true if data is output to SDRAM on sDOut
      dqmh                 : out std_logic;  -- enable upper-byte of SDRAM databus if true
      dqml                 : out std_logic  -- enable lower-byte of SDRAM databus if true
      );
  end component;
 
  -- dual-port interface to the SDRAM controller
  component dualport
    generic(
      PIPE_EN         :    boolean                       := false;  -- enable pipelined read operations
      PORT_TIME_SLOTS :    std_logic_vector(15 downto 0) := "1111000011110000";
      DATA_WIDTH      :    natural                       := 16;  -- host & SDRAM data width
      HADDR_WIDTH     :    natural                       := 23  -- host-side address width
      );
    port(
      clk             : in std_logic;   -- master clock
 
      -- host-side port 0
      rst0          : in  std_logic;    -- reset
      rd0           : in  std_logic;    -- initiate read operation
      wr0           : in  std_logic;    -- initiate write operation
      uds0          : in  std_logic;	 -- upper data strobe
      lds0          : in  std_logic;	 -- lower data strobe
      earlyOpBegun0 : out std_logic;    -- read/write op has begun (async)
      opBegun0      : out std_logic;    -- read/write op has begun (clocked)
      rdPending0    : out std_logic;    -- true if read operation(s) are still in the pipeline
      done0         : out std_logic;    -- read or write operation is done
      rdDone0       : out std_logic;    -- read operation is done and data is available
      hAddr0        : in  std_logic_vector(HADDR_WIDTH-1 downto 0);  -- address from host to SDRAM
      hDIn0         : in  std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from host to SDRAM
      hDOut0        : out std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from SDRAM to host
      status0       : out std_logic_vector(3 downto 0);  -- diagnostic status of the SDRAM controller FSM         
 
      -- host-side port 1
      rst1          : in  std_logic;
      rd1           : in  std_logic;
      wr1           : in  std_logic;
      uds1          : in  std_logic;
      lds1          : in  std_logic;
      earlyOpBegun1 : out std_logic;
      opBegun1      : out std_logic;
      rdPending1    : out std_logic;
      done1         : out std_logic;
      rdDone1       : out std_logic;
      hAddr1        : in  std_logic_vector(HADDR_WIDTH-1 downto 0);
      hDIn1         : in  std_logic_vector(DATA_WIDTH-1 downto 0);
      hDOut1        : out std_logic_vector(DATA_WIDTH-1 downto 0);
      status1       : out std_logic_vector(3 downto 0);
 
      -- SDRAM controller port
      rst          : out std_logic;
      rd           : out std_logic;
      wr           : out std_logic;
      earlyOpBegun : in  std_logic;
      opBegun      : in  std_logic;
      rdPending    : in  std_logic;
      done         : in  std_logic;
      rdDone       : in  std_logic;
      hAddr        : out std_logic_vector(HADDR_WIDTH-1 downto 0);
      hDIn         : out std_logic_vector(DATA_WIDTH-1 downto 0);
      hDOut        : in  std_logic_vector(DATA_WIDTH-1 downto 0);
      status       : in  std_logic_vector(3 downto 0)
      );
  end component;
 
end package sdram;
 
 
 
 
--------------------------------------------------------------------
-- Company : XESS Corp.
-- Engineer : Dave Vanden Bout
-- Creation Date : 05/17/2005
-- Copyright : 2005, XESS Corp
-- Tool Versions : WebPACK 6.3.03i
--
-- Description:
-- SDRAM controller
--
-- Revision:
-- 1.5.0
--
-- Additional Comments:
-- 1.5.0:
-- John Kent 2008-03-28
-- added upper and lower data strobes.
-- 1.4.0:
-- Added generic parameter to enable/disable independent active rows in each bank.
-- 1.3.0:
-- Modified to allow independently active rows in each bank.
-- 1.2.0:
-- Modified to allow pipelining of read/write operations.
-- 1.1.0:
-- Initial release.
--
-- License:
-- This code can be freely distributed and modified as long as
-- this header is not removed.
--------------------------------------------------------------------
 
library IEEE, UNISIM;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use IEEE.numeric_std.all;
use WORK.common.all;
 
entity sdramCntl is
  generic(
    FREQ                 :     natural := 100_000;  -- operating frequency in KHz
    IN_PHASE             :     boolean := true;  -- SDRAM and controller work on same or opposite clock edge
    PIPE_EN              :     boolean := false;  -- if true, enable pipelined read operations
    MAX_NOP              :     natural := 10000;  -- number of NOPs before entering self-refresh
    MULTIPLE_ACTIVE_ROWS :     boolean := false;  -- if true, allow an active row in each bank
    DATA_WIDTH           :     natural := 16;  -- host & SDRAM data width
    NROWS                :     natural := 8192;  -- number of rows in SDRAM array
    NCOLS                :     natural := 512;  -- number of columns in SDRAM array
    HADDR_WIDTH          :     natural := 24;  -- host-side address width
    SADDR_WIDTH          :     natural := 13  -- SDRAM-side address width
    );
  port(
    -- host side
    clk                  : in  std_logic;  -- master clock
    lock                 : in  std_logic;  -- true if clock is stable
    rst                  : in  std_logic;  -- reset
    rd                   : in  std_logic;  -- initiate read operation
    wr                   : in  std_logic;  -- initiate write operation
    uds                  : in  std_logic;  -- upper data strobe
    lds                  : in  std_logic;  -- lower data strobe
    earlyOpBegun         : out std_logic;  -- read/write/self-refresh op has begun (async)
    opBegun              : out std_logic;  -- read/write/self-refresh op has begun (clocked)
    rdPending            : out std_logic;  -- true if read operation(s) are still in the pipeline
    done                 : out std_logic;  -- read or write operation is done
    rdDone               : out std_logic;  -- read operation is done and data is available
    hAddr                : in  std_logic_vector(HADDR_WIDTH-1 downto 0);  -- address from host to SDRAM
    hDIn                 : in  std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from host       to SDRAM
    hDOut                : out std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from SDRAM to host
    status               : out std_logic_vector(3 downto 0);  -- diagnostic status of the FSM         
 
    -- SDRAM side
    cke     : out std_logic;            -- clock-enable to SDRAM
    ce_n    : out std_logic;            -- chip-select to SDRAM
    ras_n   : out std_logic;            -- SDRAM row address strobe
    cas_n   : out std_logic;            -- SDRAM column address strobe
    we_n    : out std_logic;            -- SDRAM write enable
    ba      : out std_logic_vector(1 downto 0);  -- SDRAM bank address
    sAddr   : out std_logic_vector(SADDR_WIDTH-1 downto 0);  -- SDRAM row/column address
    sDIn    : in  std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from SDRAM
    sDOut   : out std_logic_vector(DATA_WIDTH-1 downto 0);  -- data to SDRAM
    sDOutEn : out std_logic;            -- true if data is output to SDRAM on sDOut
    dqmh    : out std_logic;            -- enable upper-byte of SDRAM databus if true
    dqml    : out std_logic             -- enable lower-byte of SDRAM databus if true
    );
end sdramCntl;
 
 
 
architecture arch of sdramCntl is
 
  constant OUTPUT : std_logic := '1';   -- direction of dataflow w.r.t. this controller
  constant INPUT  : std_logic := '0';
  constant NOP    : std_logic := '0';   -- no operation
  constant READ   : std_logic := '1';   -- read operation
  constant WRITE  : std_logic := '1';   -- write operation
 
  -- SDRAM timing parameters
  constant Tinit : natural := 200;      -- min initialization interval (us)
  constant Tras  : natural := 45;       -- min interval between active to precharge commands (ns)
  constant Trcd  : natural := 20;       -- min interval between active and R/W commands (ns)
  constant Tref  : natural := 64_000_000;  -- maximum refresh interval (ns)
  constant Trfc  : natural := 66;       -- duration of refresh operation (ns)
  constant Trp   : natural := 20;       -- min precharge command duration (ns)
  constant Twr   : natural := 15;       -- write recovery time (ns)
  constant Txsr  : natural := 75;       -- exit self-refresh time (ns)
 
  -- SDRAM timing parameters converted into clock cycles (based on FREQ)
  constant NORM        : natural := 1_000_000;  -- normalize ns * KHz
  constant INIT_CYCLES : natural := 1+((Tinit*FREQ)/1000);  -- SDRAM power-on initialization interval
  constant RAS_CYCLES  : natural := 1+((Tras*FREQ)/NORM);  -- active-to-precharge interval
  constant RCD_CYCLES  : natural := 1+((Trcd*FREQ)/NORM);  -- active-to-R/W interval
  constant REF_CYCLES  : natural := 1+(((Tref/NROWS)*FREQ)/NORM);  -- interval between row refreshes
  constant RFC_CYCLES  : natural := 1+((Trfc*FREQ)/NORM);  -- refresh operation interval
  constant RP_CYCLES   : natural := 1+((Trp*FREQ)/NORM);  -- precharge operation interval
  constant WR_CYCLES   : natural := 1+((Twr*FREQ)/NORM);  -- write recovery time
  constant XSR_CYCLES  : natural := 1+((Txsr*FREQ)/NORM);  -- exit self-refresh time
  constant MODE_CYCLES : natural := 2;  -- mode register setup time
  constant CAS_CYCLES  : natural := 3;  -- CAS latency
  constant RFSH_OPS    : natural := 8;  -- number of refresh operations needed to init SDRAM
 
  -- timer registers that count down times for various SDRAM operations
  signal timer_r, timer_x       : natural range 0 to INIT_CYCLES;  -- current SDRAM op time
  signal rasTimer_r, rasTimer_x : natural range 0 to RAS_CYCLES;  -- active-to-precharge time
  signal wrTimer_r, wrTimer_x   : natural range 0 to WR_CYCLES;  -- write-to-precharge time
  signal refTimer_r, refTimer_x : natural range 0 to REF_CYCLES;  -- time between row refreshes
  signal rfshCntr_r, rfshCntr_x : natural range 0 to NROWS;  -- counts refreshes that are neede
  signal nopCntr_r, nopCntr_x   : natural range 0 to MAX_NOP;  -- counts consecutive NOP operations
 
  signal doSelfRfsh : std_logic;        -- active when the NOP counter hits zero and self-refresh can start
 
  -- states of the SDRAM controller state machine
  type cntlState is (
    INITWAIT,                           -- initialization - waiting for power-on initialization to complete
    INITPCHG,                           -- initialization - initial precharge of SDRAM banks
    INITSETMODE,                        -- initialization - set SDRAM mode
    INITRFSH,                           -- initialization - do initial refreshes
    RW,                                 -- read/write/refresh the SDRAM
    ACTIVATE,                           -- open a row of the SDRAM for reading/writing
    REFRESHROW,                         -- refresh a row of the SDRAM
    SELFREFRESH                         -- keep SDRAM in self-refresh mode with CKE low
    );
  signal state_r, state_x : cntlState;  -- state register and next state
 
  -- commands that are sent to the SDRAM to make it perform certain operations
  -- commands use these SDRAM input pins (ce_n,ras_n,cas_n,we_n,dqmh,dqml)
--  subtype sdramCmd is unsigned(5 downto 0);
--  constant NOP_CMD    : sdramCmd := "011100";
--  constant ACTIVE_CMD : sdramCmd := "001100";
--  constant READ_CMD   : sdramCmd := "010100";
--  constant WRITE_CMD  : sdramCmd := "010000";
--  constant PCHG_CMD   : sdramCmd := "001011";
--  constant MODE_CMD   : sdramCmd := "000011";
--  constant RFSH_CMD   : sdramCmd := "000111";
 
  -- commands that are sent to the SDRAM to make it perform certain operations
  -- commands use these SDRAM input pins (ce_n,ras_n,cas_n,we_n)
  subtype sdramCmd is unsigned(3 downto 0);
  constant NOP_CMD    : sdramCmd := "0111";
  constant ACTIVE_CMD : sdramCmd := "0011";
  constant READ_CMD   : sdramCmd := "0101";
  constant WRITE_CMD  : sdramCmd := "0100";
  constant PCHG_CMD   : sdramCmd := "0010";
  constant MODE_CMD   : sdramCmd := "0000";
  constant RFSH_CMD   : sdramCmd := "0001";
 
  -- SDRAM mode register
  -- the SDRAM is placed in a non-burst mode (burst length = 1) with a 3-cycle CAS
  subtype sdramMode is std_logic_vector(12 downto 0);
  constant MODE : sdramMode := "000" & "0" & "00" & "011" & "0" & "000";
 
  -- the host address is decomposed into these sets of SDRAM address components
  constant ROW_LEN : natural := log2(NROWS);  -- number of row address bits
  constant COL_LEN : natural := log2(NCOLS);  -- number of column address bits
  signal   bank    : std_logic_vector(ba'range);  -- bank address bits
  signal   row     : std_logic_vector(ROW_LEN - 1 downto 0);  -- row address within bank
  signal   col     : std_logic_vector(sAddr'range);  -- column address within row
 
  -- registers that store the currently active row in each bank of the SDRAM
  constant NUM_ACTIVE_ROWS            : integer := int_select(MULTIPLE_ACTIVE_ROWS = false, 1, 2**ba'length);
  type activeRowType is array(0 to NUM_ACTIVE_ROWS-1) of std_logic_vector(row'range);
  signal   activeRow_r, activeRow_x   : activeRowType;
  signal   activeFlag_r, activeFlag_x : std_logic_vector(0 to NUM_ACTIVE_ROWS-1);  -- indicates that some row in a bank is active
  signal   bankIndex                  : natural range 0 to NUM_ACTIVE_ROWS-1;  -- bank address bits
  signal   activeBank_r, activeBank_x : std_logic_vector(ba'range);  -- indicates the bank with the active row
  signal   doActivate                 : std_logic;  -- indicates when a new row in a bank needs to be activated
 
  -- there is a command bit embedded within the SDRAM column address
  constant CMDBIT_POS    : natural   := 10;  -- position of command bit
  constant AUTO_PCHG_ON  : std_logic := '1';  -- CMDBIT value to auto-precharge the bank
  constant AUTO_PCHG_OFF : std_logic := '0';  -- CMDBIT value to disable auto-precharge
  constant ONE_BANK      : std_logic := '0';  -- CMDBIT value to select one bank
  constant ALL_BANKS     : std_logic := '1';  -- CMDBIT value to select all banks
 
  -- status signals that indicate when certain operations are in progress
  signal wrInProgress       : std_logic;  -- write operation in progress
  signal rdInProgress       : std_logic;  -- read operation in progress
  signal activateInProgress : std_logic;  -- row activation is in progress
 
  -- these registers track the progress of read and write operations
  signal rdPipeline_r, rdPipeline_x : std_logic_vector(CAS_CYCLES+1 downto 0);  -- pipeline of read ops in progress
  signal wrPipeline_r, wrPipeline_x : std_logic_vector(0 downto 0);  -- pipeline of write ops (only need 1 cycle)
 
  -- registered outputs to host
  signal opBegun_r, opBegun_x             : std_logic;  -- true when SDRAM read or write operation is started
  signal hDOut_r, hDOut_x                 : std_logic_vector(hDOut'range);  -- holds data read from SDRAM and sent to the host
  signal hDOutOppPhase_r, hDOutOppPhase_x : std_logic_vector(hDOut'range);  -- holds data read from SDRAM   on opposite clock edge
 
  -- registered outputs to SDRAM
  signal cke_r, cke_x           : std_logic;  -- clock enable 
  signal cmd_r, cmd_x           : sdramCmd;  -- SDRAM command bits
  signal ba_r, ba_x             : std_logic_vector(ba'range);  -- SDRAM bank address bits
  signal sAddr_r, sAddr_x       : std_logic_vector(sAddr'range);  -- SDRAM row/column address
  signal sData_r, sData_x       : std_logic_vector(sDOut'range);  -- SDRAM out databus
  signal dqmh_r, dqmh_x         : std_logic;  -- SDRAM upper data mask
  signal dqml_r, dqml_x         : std_logic;  -- SDRAM lower data mask
  signal sDataDir_r, sDataDir_x : std_logic;  -- SDRAM databus direction control bit
 
begin
 
assign_single_port : process( cmd_r, dqmh_r, dqml_r, cke_r, 
                              ba_r, sAddr_r, 
							         sData_r, sDataDir_r,
                              hDOut_r, opBegun_r )
begin
  -----------------------------------------------------------
  -- attach some internal signals to the I/O ports 
  -----------------------------------------------------------
 
  -- attach registered SDRAM control signals to SDRAM input pins
  (ce_n, ras_n, cas_n, we_n) <= cmd_r;  -- SDRAM operation control bits
  dqmh				           <= dqmh_r;
  dqml                       <= dqml_r;
  cke                        <= cke_r;  -- SDRAM clock enable
  ba                         <= ba_r;  -- SDRAM bank address
  sAddr                      <= sAddr_r;  -- SDRAM address
  sDOut                      <= sData_r;  -- SDRAM output data bus
  if sDataDir_r = OUTPUT then
     sDOutEn                 <= YES; 
  else 
     sDOutEn                 <= NO;  -- output databus enable
  end if;
  -- attach some port signals
  hDOut   <= hDOut_r;                   -- data back to host
  opBegun <= opBegun_r;                 -- true if requested operation has begun
end process;
 
 
  -----------------------------------------------------------
  -- compute the next state and outputs 
  -----------------------------------------------------------
 
  combinatorial : process(rd, wr, hAddr, hDIn, hDOut_r, sDIn, state_r, opBegun_x,
                          activeFlag_r, activeRow_r, rdPipeline_r, wrPipeline_r,
                          hDOutOppPhase_r, nopCntr_r, lock, rfshCntr_r, timer_r, rasTimer_r,
                          wrTimer_r, refTimer_r, cmd_r, uds, lds, cke_r, activeBank_r, ba_r )
  begin
 
    -----------------------------------------------------------
    -- setup default values for signals 
    -----------------------------------------------------------
 
    opBegun_x    <= NO;                 -- no operations have begun
    earlyOpBegun <= opBegun_x;
    cke_x        <= YES;                -- enable SDRAM clock
    cmd_x        <= NOP_CMD;            -- set SDRAM command to no-operation
    dqmh_x       <= '0';
	 dqml_x       <= '0';
    sDataDir_x   <= INPUT;              -- accept data from the SDRAM
    sData_x      <= hDIn(sData_x'range);  -- output data from host to SDRAM
    state_x      <= state_r;            -- reload these registers and flags
    activeFlag_x <= activeFlag_r;       --              with their existing values
    activeRow_x  <= activeRow_r;
    activeBank_x <= activeBank_r;
    rfshCntr_x   <= rfshCntr_r;
 
    -----------------------------------------------------------
    -- setup default value for the SDRAM address 
    -----------------------------------------------------------
 
    -- extract bank field from host address
    ba_x                    <= hAddr(ba'length + ROW_LEN + COL_LEN - 1 downto ROW_LEN + COL_LEN);
    if MULTIPLE_ACTIVE_ROWS = true then
      bank                  <= (others => '0');
      bankIndex             <= CONV_INTEGER(ba_x);
    else
      bank                  <= ba_x;
      bankIndex             <= 0;
    end if;
    -- extract row, column fields from host address
    row                     <= hAddr(ROW_LEN + COL_LEN - 1 downto COL_LEN);
    -- extend column (if needed) until it is as large as the (SDRAM address bus - 1)
    col                     <= (others => '0');  -- set it to all zeroes
    col(COL_LEN-1 downto 0) <= hAddr(COL_LEN-1 downto 0);
    -- by default, set SDRAM address to the column address with interspersed
    -- command bit set to disable auto-precharge
    sAddr_x                 <= col(col'high downto CMDBIT_POS+1) & AUTO_PCHG_OFF
                               & col(CMDBIT_POS-1 downto 0);
 
    -----------------------------------------------------------
    -- manage the read and write operation pipelines
    -----------------------------------------------------------
 
    -- determine if read operations are in progress by the presence of
    -- READ flags in the read pipeline 
    if rdPipeline_r(rdPipeline_r'high downto 1) /= 0 then
      rdInProgress <= YES;
    else
      rdInProgress <= NO;
    end if;
    rdPending      <= rdInProgress;     -- tell the host if read operations are in progress
 
    -- enter NOPs into the read and write pipeline shift registers by default
    rdPipeline_x    <= NOP & rdPipeline_r(rdPipeline_r'high downto 1);
    wrPipeline_x(0) <= NOP;
 
    -- transfer data from SDRAM to the host data register if a read flag has exited the pipeline
    -- (the transfer occurs 1 cycle before we tell the host the read operation is done)
    if rdPipeline_r(1) = READ then
      hDOutOppPhase_x <= sDIn(hDOut'range);  -- gets value on the SDRAM databus on the opposite phase
      if IN_PHASE then
        -- get the SDRAM data for the host directly from the SDRAM if the controller and SDRAM are in-phase
        hDOut_x       <= sDIn(hDOut'range);
      else
        -- otherwise get the SDRAM data that was gathered on the previous opposite clock edge
        hDOut_x       <= hDOutOppPhase_r(hDOut'range);
      end if;
    else
      -- retain contents of host data registers if no data from the SDRAM has arrived yet
      hDOutOppPhase_x <= hDOutOppPhase_r;
      hDOut_x         <= hDOut_r;
    end if;
 
    done   <= rdPipeline_r(0) or wrPipeline_r(0);  -- a read or write operation is done
    rdDone <= rdPipeline_r(0);          -- SDRAM data available when a READ flag exits the pipeline 
 
    -----------------------------------------------------------
    -- manage row activation
    -----------------------------------------------------------
 
    -- request a row activation operation if the row of the current address
    -- does not match the currently active row in the bank, or if no row
    -- in the bank is currently active
    if (bank /= activeBank_r) or (row /= activeRow_r(bankIndex)) or (activeFlag_r(bankIndex) = NO) then
      doActivate <= YES;
    else
      doActivate <= NO;
    end if;
 
    -----------------------------------------------------------
    -- manage self-refresh
    -----------------------------------------------------------
 
    -- enter self-refresh if neither a read or write is requested for MAX_NOP consecutive cycles.
    if (rd = YES) or (wr = YES) then
      -- any read or write resets NOP counter and exits self-refresh state
      nopCntr_x  <= 0;
      doSelfRfsh <= NO;
    elsif nopCntr_r /= MAX_NOP then
      -- increment NOP counter whenever there is no read or write operation 
      nopCntr_x  <= nopCntr_r + 1;
      doSelfRfsh <= NO;
    else
      -- start self-refresh when counter hits maximum NOP count and leave counter unchanged
      nopCntr_x  <= nopCntr_r;
      doSelfRfsh <= YES;
    end if;
 
    -----------------------------------------------------------
    -- update the timers 
    -----------------------------------------------------------
 
    -- row activation timer
    if rasTimer_r /= 0 then
      -- decrement a non-zero timer and set the flag
      -- to indicate the row activation is still inprogress
      rasTimer_x         <= rasTimer_r - 1;
      activateInProgress <= YES;
    else
      -- on timeout, keep the timer at zero     and reset the flag
      -- to indicate the row activation operation is done
      rasTimer_x         <= rasTimer_r;
      activateInProgress <= NO;
    end if;
 
    -- write operation timer            
    if wrTimer_r /= 0 then
      -- decrement a non-zero timer and set the flag
      -- to indicate the write operation is still inprogress
      wrTimer_x    <= wrTimer_r - 1;
      wrInPRogress <= YES;
    else
      -- on timeout, keep the timer at zero and reset the flag that
      -- indicates a write operation is in progress
      wrTimer_x    <= wrTimer_r;
      wrInPRogress <= NO;
    end if;
 
    -- refresh timer            
    if refTimer_r /= 0 then
      refTimer_x <= refTimer_r - 1;
    else
      -- on timeout, reload the timer with the interval between row refreshes
      -- and increment the counter for the number of row refreshes that are needed
      refTimer_x <= REF_CYCLES;
      rfshCntr_x <= rfshCntr_r + 1;
    end if;
 
    -- main timer for sequencing SDRAM operations               
    if timer_r /= 0 then
      -- decrement the timer and do nothing else since the previous operation has not completed yet.
      timer_x <= timer_r - 1;
      status  <= "0000";
    else
      -- the previous operation has completed once the timer hits zero
      timer_x <= timer_r;               -- by default, leave the timer at zero
 
      -----------------------------------------------------------
      -- compute the next state and outputs 
      -----------------------------------------------------------
      case state_r is
 
        -----------------------------------------------------------
        -- let clock stabilize and then wait for the SDRAM to initialize 
        -----------------------------------------------------------
        when INITWAIT =>
          if lock = YES then
                                        -- wait for SDRAM power-on initialization once the clock is stable
            timer_x <= INIT_CYCLES;     -- set timer for initialization duration
            state_x <= INITPCHG;
          else
                                        -- disable SDRAM clock and return to this state if the clock is not stable
                                        -- this insures the clock is stable before enabling the SDRAM
                                        -- it also insures a clean startup if the SDRAM is currently in self-refresh mode
            cke_x   <= NO;
          end if;
          status    <= "0001";
 
          -----------------------------------------------------------
          -- precharge all SDRAM banks after power-on initialization 
          -----------------------------------------------------------
        when INITPCHG =>
          cmd_x               <= PCHG_CMD;
			 dqmh_x              <= '1';
			 dqml_x              <= '1';
          sAddr_x(CMDBIT_POS) <= ALL_BANKS;  -- precharge all banks
          timer_x             <= RP_CYCLES;  -- set timer for precharge operation duration
          rfshCntr_x          <= RFSH_OPS;  -- set counter for refresh ops needed after precharge
          state_x             <= INITRFSH;
          status              <= "0010";
 
          -----------------------------------------------------------
          -- refresh the SDRAM a number of times after initial precharge 
          -----------------------------------------------------------
        when INITRFSH =>
          cmd_x      <= RFSH_CMD;
			 dqmh_x     <= '1';
			 dqml_x     <= '1';
          timer_x    <= RFC_CYCLES;     -- set timer to refresh operation duration
          rfshCntr_x <= rfshCntr_r - 1;  -- decrement refresh operation counter
          if rfshCntr_r = 1 then
            state_x  <= INITSETMODE;    -- set the SDRAM mode once all refresh ops are done
          end if;
          status     <= "0011";
 
          -----------------------------------------------------------
          -- set the mode register of the SDRAM 
          -----------------------------------------------------------
        when INITSETMODE =>
          cmd_x   <= MODE_CMD;
			 dqmh_x  <= '1';
			 dqml_x  <= '1';
          sAddr_x <= MODE;              -- output mode register bits on the SDRAM address bits
          timer_x <= MODE_CYCLES;       -- set timer for mode setting operation duration
          state_x <= RW;
          status  <= "0100";
 
          -----------------------------------------------------------
          -- process read/write/refresh operations after initialization is done 
          -----------------------------------------------------------
        when RW                                      =>
          -----------------------------------------------------------
          -- highest priority operation: row refresh 
          -- do a refresh operation if the refresh counter is non-zero
          -----------------------------------------------------------
          if rfshCntr_r /= 0 then
                                        -- wait for any row activations, writes or reads to finish before doing a precharge
            if (activateInProgress = NO) and (wrInProgress = NO) and (rdInProgress = NO) then
              cmd_x                       <= PCHG_CMD;  -- initiate precharge of the SDRAM
              dqmh_x                      <= '1';
              dqml_x                      <= '1';
              sAddr_x(CMDBIT_POS)         <= ALL_BANKS;  -- precharge all banks
              timer_x                     <= RP_CYCLES;  -- set timer for this operation
              activeFlag_x                <= (others => NO);  -- all rows are inactive after a precharge operation
              state_x                     <= REFRESHROW;  -- refresh the SDRAM after the precharge
            end if;
            status                        <= "0101";
            -----------------------------------------------------------
            -- do a host-initiated read operation 
            -----------------------------------------------------------
          elsif rd = YES then
					  -- Wait one clock cycle if the bank address has just changed and each bank has its own active row.
            -- This gives extra time for the row activation circuitry.
            if (ba_x = ba_r) or (MULTIPLE_ACTIVE_ROWS=false) then
                                        -- activate a new row if the current read is outside the active row or bank
              if doActivate = YES then
                                        -- activate new row only if all previous activations, writes, reads are done
                if (activateInProgress = NO) and (wrInProgress = NO) and (rdInProgress = NO) then
                  cmd_x                   <= PCHG_CMD;  -- initiate precharge of the SDRAM
                  dqmh_x                  <= '1';
                  dqml_x                  <= '1';
                  sAddr_x(CMDBIT_POS)     <= ONE_BANK;  -- precharge this bank
                  timer_x                 <= RP_CYCLES;  -- set timer for this operation
                  activeFlag_x(bankIndex) <= NO;  -- rows in this bank are inactive after a precharge operation
                  state_x                 <= ACTIVATE;  -- activate the new row after the precharge is done
                end if;
                                        -- read from the currently active row if no previous read operation
                                        -- is in progress or if pipeline reads are enabled
                                        -- we can always initiate a read even if a write is already in progress
              elsif (rdInProgress = NO) or PIPE_EN then
                cmd_x                     <= READ_CMD;  -- initiate a read of the SDRAM
                                        -- insert a flag into the pipeline shift register that will exit the end
                                        -- of the shift register when the data from the SDRAM is available
                dqmh_x                    <= not uds;
                dqml_x                    <= not lds;
                rdPipeline_x              <= READ & rdPipeline_r(rdPipeline_r'high downto 1);
                opBegun_x                 <= YES;  -- tell the host the requested operation has begun
              end if;
            end if;
            status                        <= "0110";
            -----------------------------------------------------------
            -- do a host-initiated write operation 
            -----------------------------------------------------------
          elsif wr = YES then
					  -- Wait one clock cycle if the bank address has just changed and each bank has its own active row.
            -- This gives extra time for the row activation circuitry.
            if (ba_x = ba_r) or (MULTIPLE_ACTIVE_ROWS=false) then
                                        -- activate a new row if the current write is outside the active row or bank
              if doActivate = YES then
                                        -- activate new row only if all previous activations, writes, reads are done
                if (activateInProgress = NO) and (wrInProgress = NO) and (rdInProgress = NO) then
                  cmd_x                   <= PCHG_CMD;  -- initiate precharge of the SDRAM
                  dqmh_x                  <= '1';
                  dqml_x                  <= '1';
                  sAddr_x(CMDBIT_POS)     <= ONE_BANK;  -- precharge this bank
                  timer_x                 <= RP_CYCLES;  -- set timer for this operation
                  activeFlag_x(bankIndex) <= NO;  -- rows in this bank are inactive after a precharge operation
                  state_x                 <= ACTIVATE;  -- activate the new row after the precharge is done
                end if;
                                        -- write to the currently active row if no previous read operations are in progress
              elsif rdInProgress = NO then
                cmd_x                     <= WRITE_CMD;  -- initiate the write operation
                dqmh_x                    <= not uds;
                dqml_x                    <= not lds;
                sDataDir_x                <= OUTPUT;  -- turn on drivers to send data to SDRAM
                                        -- set timer so precharge doesn't occur too soon after write operation
                wrTimer_x                 <= WR_CYCLES;
                                        -- insert a flag into the 1-bit pipeline shift register that will exit on the
                                        -- next cycle.  The write into SDRAM is not actually done by that time, but
                                        -- this doesn't matter to the host
                wrPipeline_x(0)           <= WRITE;
                opBegun_x                 <= YES;  -- tell the host the requested operation has begun
              end if;
            end if;
            status                        <= "0111";
            -----------------------------------------------------------
            -- do a host-initiated self-refresh operation 
            -----------------------------------------------------------
          elsif doSelfRfsh = YES then
                                        -- wait until all previous activations, writes, reads are done
            if (activateInProgress = NO) and (wrInProgress = NO) and (rdInProgress = NO) then
              cmd_x                       <= PCHG_CMD;  -- initiate precharge of the SDRAM
              dqmh_x                       <= '1';
              dqml_x                       <= '1';
              sAddr_x(CMDBIT_POS)         <= ALL_BANKS;  -- precharge all banks
              timer_x                     <= RP_CYCLES;  -- set timer for this operation
              activeFlag_x                <= (others => NO);  -- all rows are inactive after a precharge operation
              state_x                     <= SELFREFRESH;  -- self-refresh the SDRAM after the precharge
            end if;
            status                        <= "1000";
            -----------------------------------------------------------
            -- no operation
            -----------------------------------------------------------
          else
            state_x                       <= RW;  -- continue to look for SDRAM operations to execute
            status                        <= "1001";
          end if;
 
          -----------------------------------------------------------
          -- activate a row of the SDRAM 
          -----------------------------------------------------------
        when ACTIVATE                        =>
          cmd_x                   <= ACTIVE_CMD;
          dqmh_x                  <= '0';
          dqml_x                  <= '0';
          sAddr_x                 <= (others => '0');  -- output the address for the row to be activated
          sAddr_x(row'range)      <= row;
          activeBank_x            <= bank;
          activeRow_x(bankIndex)  <= row;  -- store the new active SDRAM row address
          activeFlag_x(bankIndex) <= YES;  -- the SDRAM is now active
          rasTimer_x              <= RAS_CYCLES;  -- minimum time before another precharge can occur 
          timer_x                 <= RCD_CYCLES;  -- minimum time before a read/write operation can occur
          state_x                 <= RW;  -- return to do read/write operation that initiated this activation
          status                  <= "1010";
 
          -----------------------------------------------------------
          -- refresh a row of the SDRAM         
          -----------------------------------------------------------
        when REFRESHROW =>
          cmd_x      <= RFSH_CMD;
          dqmh_x     <= '1';
          dqml_x     <= '1';
          timer_x    <= RFC_CYCLES;     -- refresh operation interval
          rfshCntr_x <= rfshCntr_r - 1;  -- decrement the number of needed row refreshes
          state_x    <= RW;             -- process more SDRAM operations after refresh is done
          status     <= "1011";
 
          -----------------------------------------------------------
          -- place the SDRAM into self-refresh and keep it there until further notice           
          -----------------------------------------------------------
        when SELFREFRESH            =>
          if (doSelfRfsh = YES) or (lock = NO) then
                                        -- keep the SDRAM in self-refresh mode as long as requested and until there is a stable clock
            cmd_x        <= RFSH_CMD;   -- output the refresh command; this is only needed on the first clock cycle
            dqmh_x       <= '1';
            dqml_x       <= '1';
            cke_x        <= NO;         -- disable the SDRAM clock
          else
                                        -- else exit self-refresh mode and start processing read and write operations
            cke_x        <= YES;        -- restart the SDRAM clock
            rfshCntr_x   <= 0;          -- no refreshes are needed immediately after leaving self-refresh
            activeFlag_x <= (others => NO);  -- self-refresh deactivates all rows
            timer_x      <= XSR_CYCLES;  -- wait this long until read and write operations can resume
            state_x      <= RW;
          end if;
          status         <= "1100";
 
          -----------------------------------------------------------
          -- unknown state
          -----------------------------------------------------------
        when others =>
          state_x <= INITWAIT;          -- reset state if in erroneous state
          status  <= "1101";
 
      end case;
    end if;
  end process combinatorial;
 
 
  -----------------------------------------------------------
  -- update registers on the appropriate clock edge     
  -----------------------------------------------------------
 
  update : process(rst, clk)
  begin
 
    if rst = YES then
      -- asynchronous reset
      state_r      <= INITWAIT;
      activeFlag_r <= (others => NO);
      rfshCntr_r   <= 0;
      timer_r      <= 0;
      refTimer_r   <= REF_CYCLES;
      rasTimer_r   <= 0;
      wrTimer_r    <= 0;
      nopCntr_r    <= 0;
      opBegun_r    <= NO;
      rdPipeline_r <= (others => '0');
      wrPipeline_r <= (others => '0');
      cke_r        <= NO;
      cmd_r        <= NOP_CMD;
		dqmh_r       <= '1';
		dqml_r       <= '1';
      ba_r         <= (others => '0');
      sAddr_r      <= (others => '0');
      sData_r      <= (others => '0');
      sDataDir_r   <= INPUT;
      hDOut_r      <= (others => '0');
    elsif rising_edge(clk) then
      state_r      <= state_x;
      activeBank_r <= activeBank_x;
      activeRow_r  <= activeRow_x;
      activeFlag_r <= activeFlag_x;
      rfshCntr_r   <= rfshCntr_x;
      timer_r      <= timer_x;
      refTimer_r   <= refTimer_x;
      rasTimer_r   <= rasTimer_x;
      wrTimer_r    <= wrTimer_x;
      nopCntr_r    <= nopCntr_x;
      opBegun_r    <= opBegun_x;
      rdPipeline_r <= rdPipeline_x;
      wrPipeline_r <= wrPipeline_x;
      cke_r        <= cke_x;
      cmd_r        <= cmd_x;
		dqmh_r       <= dqmh_x;
		dqml_r       <= dqml_x;
      ba_r         <= ba_x;
      sAddr_r      <= sAddr_x;
      sData_r      <= sData_x;
      sDataDir_r   <= sDataDir_x;
      hDOut_r      <= hDOut_x;
    end if;
 
    -- the register that gets data from the SDRAM and holds it for the host
    -- is clocked on the opposite edge.  We don't use this register if IN_PHASE=TRUE.
    if rst = YES then
      hDOutOppPhase_r <= (others => '0');
    elsif falling_edge(clk) then
      hDOutOppPhase_r <= hDOutOppPhase_x;
    end if;
 
  end process update;
 
end arch;
 
 
 
 
--------------------------------------------------------------------
-- Company : XESS Corp.
-- Engineer : Dave Vanden Bout
-- Creation Date : 06/01/2005
-- Copyright : 2005, XESS Corp
-- Tool Versions : WebPACK 6.3.03i
--
-- Description:
-- Dual-port front-end for SDRAM controller. Supports two
-- independent I/O ports to the SDRAM.
--
-- Revision:
-- 1.2.0:
--     added upper and lower data strobe
--     John Kent - 2008-03-23
--
-- 1.0.0
--     Dave Vanden Bout - 2005-01-06
--
-- Additional Comments:
--
-- License:
-- This code can be freely distributed and modified as long as
-- this header is not removed.
--------------------------------------------------------------------
 
library IEEE, UNISIM;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use IEEE.numeric_std.all;
use WORK.common.all;
 
entity dualport is
  generic(
    PIPE_EN         :    boolean                       := false;  -- enable pipelined read operations
    PORT_TIME_SLOTS :    std_logic_vector(15 downto 0) := "1111000011110000";
    DATA_WIDTH      :    natural                       := 16;  -- host & SDRAM data width
    HADDR_WIDTH     :    natural                       := 23  -- host-side address width
    );
  port(
    clk             : in std_logic;     -- master clock
 
    -- host-side port 0
    rst0          : in  std_logic;      -- reset
    rd0           : in  std_logic;      -- initiate read operation
    wr0           : in  std_logic;      -- initiate write operation
    uds0          : in  std_logic;      -- upper data strobe
    lds0          : in  std_logic;      -- lower data strobe
    earlyOpBegun0 : out std_logic;      -- read/write op has begun (async)
    opBegun0      : out std_logic;      -- read/write op has begun (clocked)
    rdPending0    : out std_logic;      -- true if read operation(s) are still in the pipeline
    done0         : out std_logic;      -- read or write operation is done
    rdDone0       : out std_logic;      -- read operation is done and data is available
    hAddr0        : in  std_logic_vector(HADDR_WIDTH-1 downto 0);  -- address from host to SDRAM
    hDIn0         : in  std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from host to SDRAM
    hDOut0        : out std_logic_vector(DATA_WIDTH-1 downto 0);  -- data from SDRAM to host
    status0       : out std_logic_vector(3 downto 0);  -- diagnostic status of the SDRAM controller FSM         
 
    -- host-side port 1
    rst1          : in  std_logic;
    rd1           : in  std_logic;
    wr1           : in  std_logic;
    uds1          : in  std_logic;      -- upper data strobe
    lds1          : in  std_logic;      -- lower data strobe
    earlyOpBegun1 : out std_logic;
    opBegun1      : out std_logic;
    rdPending1    : out std_logic;
    done1         : out std_logic;
    rdDone1       : out std_logic;
    hAddr1        : in  std_logic_vector(HADDR_WIDTH-1 downto 0);
    hDIn1         : in  std_logic_vector(DATA_WIDTH-1 downto 0);
    hDOut1        : out std_logic_vector(DATA_WIDTH-1 downto 0);
    status1       : out std_logic_vector(3 downto 0);
 
    -- SDRAM controller port
    rst          : out std_logic;
    rd           : out std_logic;
    wr           : out std_logic;
    uds          : out std_logic;      -- upper data strobe
    lds          : out std_logic;      -- lower data strobe
    earlyOpBegun : in  std_logic;
    opBegun      : in  std_logic;
    rdPending    : in  std_logic;
    done         : in  std_logic;
    rdDone       : in  std_logic;
    hAddr        : out std_logic_vector(HADDR_WIDTH-1 downto 0);
    hDIn         : out std_logic_vector(DATA_WIDTH-1 downto 0);
    hDOut        : in  std_logic_vector(DATA_WIDTH-1 downto 0);
    status       : in  std_logic_vector(3 downto 0)
    );
end dualport;
 
 
 
architecture arch of dualport is
  -- The door signal controls whether the read/write signal from the active port
  -- is allowed through to the read/write inputs of the SDRAM controller.
  type doorState is (OPENED, CLOSED);
  signal door_r, door_x : doorState;
 
  -- The port signal indicates which port is connected to the SDRAM controller.
  type portState is (PORT0, PORT1);
  signal port_r, port_x : portState;
 
  signal switch                           : std_logic;  -- indicates that the active port should be switched
  signal inProgress                       : std_logic;  -- the active port has a read/write op in-progress
  signal rd_i                             : std_logic;  -- read signal to the SDRAM controller (internal copy)
  signal wr_i                             : std_logic;  -- write signal to the SDRAM controller (internal copy)
  signal earlyOpBegun0_i, earlyOpBegun1_i : std_logic;  -- (internal copies)
  signal slot_r, slot_x                   : std_logic_vector(PORT_TIME_SLOTS'range);  -- time-slot allocation shift-register
begin
 
assign_dual_ports : process( port_r, hAddr0, hAddr1, hDIn0, hDIn1, uds0, uds1, lds0, lds1,
                             hDout, status, rst0, rst1, rd0, rd1, wr0, wr1, door_r,
                             earlyOpBegun, earlyOpBegun0_i, earlyOpBegun1_i,
                             rdPending, Done, rdDone, rd_i, wr_i, slot_r )
begin
  ----------------------------------------------------------------------------
  -- multiplex the SDRAM controller port signals to/from the dual host-side ports  
  ----------------------------------------------------------------------------
 
  -- send the SDRAM controller the address and data from the currently active port
  if port_r = PORT0 then
    hAddr   <= hAddr0; 
    hDIn    <= hDIn0;  
    uds     <= uds0;   
    lds     <= lds0;   
  -- send the SDRAM controller status to the active port and give the inactive port an inactive status code
    status0 <= status;
	 status1 <= "1111";
  -- apply the read and write signals from the active port to the SDRAM controller only if the door is open.
	 if door_r = OPENED then
	   rd_i <= rd0;
		wr_i <= wr0;
	 else
	   rd_i <= NO;
		wr_i <= NO;
    end if; 
    earlyOpBegun0_i <= earlyOpBegun;
    earlyOpBegun1_i <= NO;
    rdPending0      <= rdPending;
    rdPending1      <= NO;
    done0           <= done;
    done1           <= NO;
    rdDone0         <= rdDone;
    rdDone1         <= NO;
  else 
    hAddr   <= hAddr1; 
    hDIn    <= hDIn1;  
    uds     <= uds1;   
    lds     <= lds1;
  -- send the SDRAM controller status to the active port and give the inactive port an inactive status code
	 status0 <= "1111";
    status1 <= status;
  -- apply the read and write signals from the active port to the SDRAM controller only if the door is open.
	 if door_r = OPENED then
	   rd_i <= rd1;
	   wr_i <= wr1;
	 else
	   rd_i <= NO;
	   wr_i <= NO;
    end if; 
    earlyOpBegun0_i <= NO;
    earlyOpBegun1_i <= earlyOpBegun;
    rdPending0      <= NO;
    rdPending1      <= rdPending;
    done0           <= NO;
    done1           <= done;
    rdDone0         <= NO;
    rdDone1         <= rdDone;
 end if;   
 
  -- both ports get the data from the SDRAM but only the active port will use it
  hDOut0 <= hDOut;
  hDOut1 <= hDOut;
 
 
  -- either port can reset the SDRAM controller
  rst <= rst0 or rst1;
 
  rd   <= rd_i;
  wr   <= wr_i;
 
  ----------------------------------------------------------------------------
  -- Indicate when the active port needs to be switched.  A switch occurs if
  -- a read or write operation is requested on the port that is not currently active and:
  -- 1) no R/W operation is being performed on the active port or 
  -- 2) a R/W operation is in progress on the active port, but the time-slot allocation 
  --    register is giving precedence to the inactive port.  (The R/W operation on the
  --    active port will be completed before the switch is made.)
  -- This rule keeps the active port from hogging all the bandwidth.
  ----------------------------------------------------------------------------
 
  if port_r = PORT0 then
    if (((rd0 = NO) and (wr0 = NO)) or (slot_r(0) = '1')) then
      switch <= (rd1 or wr1);
    else 
      switch <= NO;
    end if;
  else
    if (((rd1 = NO) and (wr1 = NO)) or (slot_r(0) = '0')) then
      switch <= (rd0 or wr0);
    else
	   switch  <= NO;
    end if;
  end if;
 
  -- send the status signals for various SDRAM controller operations back to the active port
  earlyOpBegun0   <= earlyOpBegun0_i;
  earlyOpBegun1   <= earlyOpBegun1_i;
 
  ----------------------------------------------------------------------------
  -- Indicate when an operation on the active port is in-progress and
  -- can't be interrupted by a switch to the other port.  (Only read operations
  -- are looked at since write operations always complete in one cycle once they
  -- are initiated.)
  ----------------------------------------------------------------------------
  inProgress <= rdPending or (rd_i and earlyOpBegun);
 
  ----------------------------------------------------------------------------
  -- Update the time-slot allocation shift-register.  The port with priority is indicated by the
  -- least-significant bit of the register.  The register is rotated right if:
  -- 1) the current R/W operation has started, and
  -- 2) both ports are requesting R/W operations (indicating contention), and
  -- 3) the currently active port matches the port that currently has priority.
  -- Under these conditions, the current time slot port allocation has been used so
  -- the shift register is rotated right to bring the next port time-slot allocation
  -- bit into play.
  ----------------------------------------------------------------------------
  if (earlyOpBegun = YES) and
     ( ((rd0 = YES) or (wr0 = YES)) and ((rd1 = YES) or (wr1 = YES)) ) and
     ( ((port_r = PORT0) and (slot_r(0) = '0')) or ((port_r = PORT1) and (slot_r(0) = '1')) ) then
    slot_x <= slot_r(0) & slot_r(slot_r'high downto 1); 
  else 
    slot_x <= slot_r;
  end if;
 
end process;
 
  ----------------------------------------------------------------------------
  -- Determine which port will be active on the next cycle.  The active port is switched if:
  -- 1) the currently active port has finished its current R/W operation, and
  -- 2) there are no pending operations in progress, and
  -- 3) the port switch indicator is active.
  ----------------------------------------------------------------------------
  port_process : process(port_r, inProgress, switch, done)
  begin
    port_x       <= port_r;             -- by default, the active port is not changed
    case port_r is
      when PORT0  =>
        if (inProgress = NO) and (switch = YES) and (PIPE_EN or (done = YES)) then
          port_x <= PORT1;
        end if;
      when PORT1  =>
        if (inProgress = NO) and (switch = YES) and (PIPE_EN or (done = YES)) then
          port_x <= PORT0;
        end if;
      when others =>
        port_x   <= port_r;
    end case;
  end process port_process;
 
  -----------------------------------------------------------
  -- Determine if the door is open for the active port to initiate new R/W operations to
  -- the SDRAM controller.  If the door is open and R/W operations are in progress but
  -- a switch to the other port is indicated, then the door is closed to prevent any
  -- further R/W operations from the active port.  The door is re-opened once all
  -- in-progress operations are completed, at which time the switch to the other port
  -- is also completed so it can issue its own R/W commands.
  -----------------------------------------------------------
  door_process : process(door_r, inProgress, switch)
  begin
    door_x       <= door_r;             -- by default, the door remains as it is
    case door_r is
      when OPENED =>
        if (inProgress = YES) and (switch = YES) then
          door_x <= CLOSED;
        end if;
      when CLOSED =>
        if inProgress = NO then
          door_x <= OPENED;
        end if;
      when others =>
        door_x   <= door_r;
    end case;
  end process door_process;
 
  -----------------------------------------------------------
  -- update registers on the appropriate clock edge     
  -----------------------------------------------------------
  update : process(rst0, rst1, clk)
  begin
    if (rst0 = YES) or (rst1 = YES) then
      -- asynchronous reset
      door_r   <= CLOSED;
      port_r   <= PORT0;
      slot_r   <= PORT_TIME_SLOTS;
      opBegun0 <= NO;
      opBegun1 <= NO;
    elsif rising_edge(clk) then
      door_r   <= door_x;
      port_r   <= port_x;
      slot_r   <= slot_x;
      -- opBegun signals are cycle-delayed versions of earlyOpBegun signals.
      -- We can't use the actual opBegun signal from the SDRAM controller
      -- because it would be turned off if the active port was switched on the
      -- cycle immediately after earlyOpBegun went active.
      opBegun0 <= earlyOpBegun0_i;
      opBegun1 <= earlyOpBegun1_i;
    end if;
  end process update;
 
end arch;