/****************************************************************************************
*
*    File Name:  ddr2.v
*      Version:  4.50
*        Model:  BUS Functional
*
* Dependencies:  ddr2_parameters.vh
*
*  Description:  Micron SDRAM DDR2 (Double Data Rate 2)
*
*   Limitation:  - doesn't check for average refresh timings
*                - model assumes clk and clk_n crossing at same edges
*                - positive dqs and dqs_n edges are used to latch data
*                - test mode is not modeled
*
*         Note:  - Set simulator resolution to "ps" accuracy
*                - Set Debug = 0 to disable $display messages
*
*   Disclaimer   This software code and all associated documentation, comments or other 
*  of Warranty:  information (collectively "Software") is provided "AS IS" without 
*                warranty of any kind. MICRON TECHNOLOGY, INC. ("MTI") EXPRESSLY 
*                DISCLAIMS ALL WARRANTIES EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED 
*                TO, NONINFRINGEMENT OF THIRD PARTY RIGHTS, AND ANY IMPLIED WARRANTIES 
*                OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. MTI DOES NOT 
*                WARRANT THAT THE SOFTWARE WILL MEET YOUR REQUIREMENTS, OR THAT THE 
*                OPERATION OF THE SOFTWARE WILL BE UNINTERRUPTED OR ERROR-FREE. 
*                FURTHERMORE, MTI DOES NOT MAKE ANY REPRESENTATIONS REGARDING THE USE OR 
*                THE RESULTS OF THE USE OF THE SOFTWARE IN TERMS OF ITS CORRECTNESS, 
*                ACCURACY, RELIABILITY, OR OTHERWISE. THE ENTIRE RISK ARISING OUT OF USE 
*                OR PERFORMANCE OF THE SOFTWARE REMAINS WITH YOU. IN NO EVENT SHALL MTI, 
*                ITS AFFILIATED COMPANIES OR THEIR SUPPLIERS BE LIABLE FOR ANY DIRECT, 
*                INDIRECT, CONSEQUENTIAL, INCIDENTAL, OR SPECIAL DAMAGES (INCLUDING, 
*                WITHOUT LIMITATION, DAMAGES FOR LOSS OF PROFITS, BUSINESS INTERRUPTION, 
*                OR LOSS OF INFORMATION) ARISING OUT OF YOUR USE OF OR INABILITY TO USE 
*                THE SOFTWARE, EVEN IF MTI HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH 
*                DAMAGES. Because some jurisdictions prohibit the exclusion or 
*                limitation of liability for consequential or incidental damages, the 
*                above limitation may not apply to you.
*
*                Copyright 2003 Micron Technology, Inc. All rights reserved.
*
* Rev   Author   Date        Changes
* ---------------------------------------------------------------------------------------
* 1.00  JMK      07/29/03    Initial Release
* 1.10  JMK      08/09/03    Timing Parameter updates to tIS, tIH, tDS, tDH
* 2.20  JMK      08/07/03    General cleanup
* 2.30  JMK      11/26/03    Added CL_MIN, CL_MAX, wl_min and wl_max parameters.
*                            Added AL_MIN and AL_MAX parameters.
*                            Removed support for OCD.
* 2.40  JMK      01/15/04    Removed verilog 2001 constructs.
* 2.50  JMK      01/29/04    Removed tRP checks during Precharge command.
* 2.60  JMK      04/20/04    Fixed tWTR check.
* 2.70  JMK      04/30/04    Added tRFC maximum check.
*                            Combined Self Refresh and Power Down always blocks.
*                            Added Reset Function (CKE LOW Anytime).
* 2.80  JMK      08/19/04    Precharge is treated as NOP when bank is not active.  
*                            Added checks for tRAS, tWR, tRTP to any bank during Pre-All.
*                            tRFC maximum violation will only display one time.
* 2.90  JMK      11/05/04    Fixed DQS checking during write.
*                            Fixed false tRFC max assertion during power up and self ref.
*                            Added warning for 200us CKE low time during initialization.
*                            Added -3, -3E, and -37V speed grades to ddr2_parameters.v
* 3.00  JMK      04/22/05    Removed ODT off requirement during power down.
*                            Added tAOND, tAOFD, tANPD, tAXPD, tAONPD, and tAOFPD parameters.
*                            Added ODT status messages.
*                            Updated the initialization sequence.
*                            Disable ODT and CLK pins during self refresh.
*                            Disable cmd and addr pins during power down and self refresh.
* 3.10  JMK      06/07/05    Disable trpa checking if the part does not have 8 banks.
*                            Changed tAXPD message from error to a warning.
*                            Added tDSS checking.
*                            Removed tDQSL checking during tWPRE and tWPST.
*                            Fixed a burst order error during writes.
*                            Renamed parameters file with .vh extension.
* 3.20  JMK      07/18/05    Removed 14 tCK requirement from LMR to READ.
* 3.30  JMK      08/03/05    Added check for interrupting a burst with auto precharge.
* 4.00  JMK      11/21/05    Parameter names all UPPERCASE, signal names all lowercase.
*                            Clock jitter can be tolerated within specification range.
*                            Clock frequency is sampled from the CK pin.
*                            Scaleable up to 64 DQ and 16 DQS bits.
*                            Read data can be randomly skewed using RANDOM_OUT_DELAY.
*                            Parameterized read and write DQS, and read DQ.
*                            Initialization can be bypassed using initialize task.
* 4.10  JMK      11/30/05    Fixed compile errors when `MAX_MEM was defined.
* 4.20  JMK      12/09/05    Fixed memory addressing error when `MAX_MEM was defined.
* 4.30  JMK      02/15/06    Added dummy write to initialization sequence.
*                            Removed tWPST maximum checking.
*                            Rising dqs_n edge latches data when enabled in EMR.
*                            Fixed a sign error in the tJIT(cc) calculation.
* 4.40  JMK      02/16/06    Fixed dummy write when`MAX_MEM was defined.
* 4.50  JMK      02/27/06    Fixed extra tDQSS assertions.
*                            Fixed tRCD and tWTR checking.
*                            Errors entering Power Down or Self Refresh will cause reset.
*                            Ignore dqs_n when disabled in EMR.
****************************************************************************************/

// DO NOT CHANGE THE TIMESCALE
// MAKE SURE YOUR SIMULATOR USES "PS" RESOLUTION
`timescale 1ps / 1ps

module ddr2 (
    ck,
    ck_n,
    cke,
    cs_n,
    ras_n,
    cas_n,
    we_n,
    dm_rdqs,
    ba,
    addr,
    dq,
    dqs,
    dqs_n,
    rdqs_n,
    odt
);

    `include "ddr2_parameters.vh"

    // text macros
    `define DQ_PER_DQS DQ_BITS/DQS_BITS
    `define BANKS      (1<<BA_BITS)
    `define MAX_BITS   (BA_BITS+ROW_BITS+COL_BITS-BL_BITS)
    `define MAX_SIZE   (1<<(BA_BITS+ROW_BITS+COL_BITS-BL_BITS))
    `define MEM_SIZE   (1<<MEM_BITS)
    `define MAX_PIPE   2*(AL_MAX + CL_MAX)

    // Declare Ports
    input   ck;
    input   ck_n;
    input   cke;
    input   cs_n;
    input   ras_n;
    input   cas_n;
    input   we_n;
    inout   [DM_BITS-1:0]   dm_rdqs;
    input   [BA_BITS-1:0]   ba;
    input   [ADDR_BITS-1:0] addr;
    inout   [DQ_BITS-1:0]   dq;
    inout   [DQS_BITS-1:0]  dqs;
    inout   [DQS_BITS-1:0]  dqs_n;
    output  [DQS_BITS-1:0]  rdqs_n;
    input   odt;
                            
    // clock jitter
    real    tck_avg;
    time    tck_sample [TDLLK-1:0];
    time    tch_sample [TDLLK-1:0];
    time    tcl_sample [TDLLK-1:0];
    time    tck_i;
    time    tch_i;
    time    tcl_i;
    real    tch_avg;
    real    tcl_avg;
    time    tm_ck_pos;
    time    tm_ck_neg;
    real    tjit_per_rtime;
    integer tjit_cc_time;
    real    terr_nper_rtime;

    // clock skew
    real    out_delay;
    integer dqsck [DQS_BITS-1:0];
    integer dqsck_min;
    integer dqsck_max;
    integer dqsq_min;
    integer dqsq_max;
    integer seed;

    // Mode Registers
    reg     burst_order;
    reg     [BL_BITS:0] burst_length;
    integer cas_latency;
    integer additive_latency;
    reg     dll_reset;
    reg     dll_locked;
    reg     dll_en;
    integer write_recovery;
    reg     low_power;
    reg     [1:0] odt_rtt;
    reg     odt_en;
    reg     [2:0] ocd;
    reg     dqs_n_en;
    reg     rdqs_en;
    reg     out_en;
    integer read_latency;
    integer write_latency;

    // cmd encoding
    parameter
        LOAD_MODE = 4'b0000,
        REFRESH   = 4'b0001,
        PRECHARGE = 4'b0010,
        ACTIVATE  = 4'b0011,
        WRITE     = 4'b0100,
        READ      = 4'b0101,
        NOP       = 4'b0111,
        PWR_DOWN  = 4'b1000,
        SELF_REF  = 4'b1001
    ;

    reg [8*9-1:0] cmd_string [9:0];
    initial begin
        cmd_string[LOAD_MODE] = "Load Mode";
        cmd_string[REFRESH  ] = "Refresh  ";
        cmd_string[PRECHARGE] = "Precharge";
        cmd_string[ACTIVATE ] = "Activate ";
        cmd_string[WRITE    ] = "Write    ";
        cmd_string[READ     ] = "Read     ";
        cmd_string[NOP      ] = "No Op    ";
        cmd_string[PWR_DOWN ] = "Pwr Down ";
        cmd_string[SELF_REF ] = "Self Ref ";
    end

    // command state
    reg     [`BANKS-1:0] active_bank;
    reg     [`BANKS-1:0] auto_precharge_bank;
    reg     [`BANKS-1:0] write_precharge_bank;
    reg     [`BANKS-1:0] read_precharge_bank;
    reg     [ROW_BITS-1:0] active_row [`BANKS-1:0];
    reg     in_power_down;
    reg     in_self_refresh;
    reg     precharge_all;
    reg     [3:0] init_mode_reg;
    reg     init_done;
    integer init_step;
    reg     er_trfc_max;
    reg     odt_state;
    reg     prev_odt;

    // cmd timers/counters