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//*****************************************************************************

//   ____  ____

//  /   /\/   /

// /___/  \  /    Vendor: Xilinx

// \   \   \/     Version: 3.0

//  \   \         Application: MIG

//  /   /         Filename: ddr2_phy_dqs_iob.v

// /___/   /\     Date Last Modified: $Date: 2008/12/23 14:26:00 $

// \   \  /  \    Date Created: Wed Aug 16 2006

//  \___\/\___\

//

//Device: Virtex-5

//Design Name: DDR2

//Purpose:

//   This module places the data strobes in the IOBs.

//Reference:

//Revision History:

//   Rev 1.1 - Parameter HIGH_PERFORMANCE_MODE added. PK. 7/10/08

//   Rev 1.2 - Parameter IODELAY_GRP added and constraint IODELAY_GROUP added

//             on IODELAY primitives. PK. 11/27/08

//*****************************************************************************

`timescale 1ns/1ps

module ddr2_phy_dqs_iob #

  (

   // Following parameters are for 72-bit RDIMM design (for ML561 Reference

   // board design). Actual values may be different. Actual parameters values

   // are passed from design top module ddr2_mig module. Please refer to

   // the ddr2_mig module for actual values.

   parameter DDR_TYPE              = 1,

   parameter HIGH_PERFORMANCE_MODE = "TRUE",

   parameter IODELAY_GRP           = "IODELAY_MIG"

   )

  (

   input        clk0,

   input        clkdiv0,

   input        rst0,

   input        dlyinc_dqs,

   input        dlyce_dqs,

   input        dlyrst_dqs,

   input        dlyinc_gate,

   input        dlyce_gate,

   input        dlyrst_gate,

   input        dqs_oe_n,

   input        dqs_rst_n,

   input        en_dqs,

   inout        ddr_dqs,

   inout        ddr_dqs_n,

   output       dq_ce,

   output       delayed_dqs

   );

  wire                     clk180;

  wire                     dqs_bufio;

  wire                     dqs_ibuf;

  wire                     dqs_idelay;

  wire                     dqs_oe_n_delay;

  wire                     dqs_oe_n_r;

  wire                     dqs_rst_n_delay;

  reg                      dqs_rst_n_r /* synthesis syn_preserve = 1*/;

  wire                     dqs_out;

  wire                     en_dqs_sync /* synthesis syn_keep = 1 */;

  // for simulation only. Synthesis should ignore this delay

  localparam    DQS_NET_DELAY = 0.8;

  assign        clk180 = ~clk0;

  // add delta delay to inputs clocked by clk180 to avoid delta-delay

  // simulation issues

  assign dqs_rst_n_delay = dqs_rst_n;

  assign dqs_oe_n_delay  = dqs_oe_n;

  //***************************************************************************

  // DQS input-side resources:

  //  - IODELAY (pad -> IDELAY)

  //  - BUFIO (IDELAY -> BUFIO)

  //***************************************************************************

  // Route DQS from PAD to IDELAY

  (* IODELAY_GROUP = IODELAY_GRP *) IODELAY #

    (

     .DELAY_SRC("I"),

     .IDELAY_TYPE("VARIABLE"),

     .HIGH_PERFORMANCE_MODE(HIGH_PERFORMANCE_MODE),

     .IDELAY_VALUE(0),

     .ODELAY_VALUE(0)

     )

    u_idelay_dqs

      (

       .DATAOUT (dqs_idelay),

       .C       (clkdiv0),

       .CE      (dlyce_dqs),

       .DATAIN  (),

       .IDATAIN (dqs_ibuf),

       .INC     (dlyinc_dqs),

       .ODATAIN (),

       .RST     (dlyrst_dqs),

       .T       ()

       );

  // From IDELAY to BUFIO

  BUFIO u_bufio_dqs

    (

     .I  (dqs_idelay),

     .O  (dqs_bufio)

     );

  // To model additional delay of DQS BUFIO + gating network

  // for behavioral simulation. Make sure to select a delay number smaller

  // than half clock cycle (otherwise output will not track input changes

  // because of inertial delay). Duplicate to avoid delta delay issues.

  assign #(DQS_NET_DELAY) i_delayed_dqs = dqs_bufio;

  assign #(DQS_NET_DELAY) delayed_dqs   = dqs_bufio;

  //***************************************************************************

  // DQS gate circuit (not supported for all controllers)

  //***************************************************************************

  // Gate routing:

  //   en_dqs -> IDELAY -> en_dqs_sync -> IDDR.S -> dq_ce ->

  //   capture IDDR.CE

  // Delay CE control so that it's in phase with delayed DQS

  (* IODELAY_GROUP = IODELAY_GRP *) IODELAY #

    (

     .DELAY_SRC             ("DATAIN"),

     .IDELAY_TYPE           ("VARIABLE"),

     .HIGH_PERFORMANCE_MODE (HIGH_PERFORMANCE_MODE),

     .IDELAY_VALUE          (0),

     .ODELAY_VALUE          (0)

     )

    u_iodelay_dq_ce

      (

       .DATAOUT (en_dqs_sync),

       .C       (clkdiv0),

       .CE      (dlyce_gate),

       .DATAIN  (en_dqs),

       .IDATAIN (),

       .INC     (dlyinc_gate),

       .ODATAIN (),

       .RST     (dlyrst_gate),

       .T       ()

       );

  // Generate sync'ed CE to DQ IDDR's using an IDDR clocked by DQS

  // We could also instantiate a negative-edge SDR flop here

  IDDR #

    (

     .DDR_CLK_EDGE ("OPPOSITE_EDGE"),

     .INIT_Q1      (1'b0),

     .INIT_Q2      (1'b0),

     .SRTYPE       ("ASYNC")

     )

    u_iddr_dq_ce

      (

       .Q1 (),

       .Q2 (dq_ce),           // output on falling edge

       .C  (i_delayed_dqs),

       .CE (1'b1),

       .D  (en_dqs_sync),

       .R  (1'b0),

       .S  (en_dqs_sync)

       );

  //***************************************************************************

  // DQS output-side resources

  //***************************************************************************

  // synthesis attribute keep of dqs_rst_n_r is "true"

  always @(posedge clk180)

    dqs_rst_n_r <= dqs_rst_n_delay;

  ODDR #

    (

     .SRTYPE("SYNC"),

     .DDR_CLK_EDGE("OPPOSITE_EDGE")

     )

    u_oddr_dqs

      (

       .Q  (dqs_out),

       .C  (clk180),

       .CE (1'b1),

       .D1 (dqs_rst_n_r),      // keep output deasserted for write preamble

       .D2 (1'b0),

       .R  (1'b0),

       .S  (1'b0)

       );

  (* IOB = "FORCE" *) FDP u_tri_state_dqs

    (

     .D   (dqs_oe_n_delay),

     .Q   (dqs_oe_n_r),

     .C   (clk180),

     .PRE (rst0)

     ) /* synthesis syn_useioff = 1 */;

  //***************************************************************************

  // use either single-ended (for DDR1) or differential (for DDR2) DQS input

  generate

    if (DDR_TYPE > 0) begin: gen_dqs_iob_ddr2

      IOBUFDS u_iobuf_dqs

        (

         .O   (dqs_ibuf),

         .IO  (ddr_dqs),

         .IOB (ddr_dqs_n),

         .I   (dqs_out),

         .T   (dqs_oe_n_r)

         );

    end else begin: gen_dqs_iob_ddr1

      IOBUF u_iobuf_dqs

        (

         .O   (dqs_ibuf),

         .IO  (ddr_dqs),

         .I   (dqs_out),

         .T   (dqs_oe_n_r)

         );

    end

  endgenerate

endmodule