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1 36 fafa1971 
/****************************************************************************************
2 
*
3 
*    File Name:  ddr.v
4 
*      Version:  5.7
5 
*        Model:  BUS Functional
6 
*
7 
* Dependencies:  ddr_parameters.v
8 
*
9 
*  Description:  Micron SDRAM DDR (Double Data Rate)
10 
*
11 
*   Limitation:  - Doesn't check for 8K-cycle refresh.
12 
*                - Doesn't check power-down entry/exit
13 
*                - Doesn't check self-refresh entry/exit.
14 
*
15 
*         Note:  - Set simulator resolution to "ps" accuracy
16 
*                - Set Debug = 0 to disable $display messages
17 
*                - Model assume Clk and Clk# crossing at both edge
18 
*
19 
*   Disclaimer   This software code and all associated documentation, comments or other
20 
*  of Warranty:  information (collectively "Software") is provided "AS IS" without
21 
*                warranty of any kind. MICRON TECHNOLOGY, INC. ("MTI") EXPRESSLY
22 
*                DISCLAIMS ALL WARRANTIES EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
23 
*                TO, NONINFRINGEMENT OF THIRD PARTY RIGHTS, AND ANY IMPLIED WARRANTIES
24 
*                OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. MTI DOES NOT
25 
*                WARRANT THAT THE SOFTWARE WILL MEET YOUR REQUIREMENTS, OR THAT THE
26 
*                OPERATION OF THE SOFTWARE WILL BE UNINTERRUPTED OR ERROR-FREE.
27 
*                FURTHERMORE, MTI DOES NOT MAKE ANY REPRESENTATIONS REGARDING THE USE OR
28 
*                THE RESULTS OF THE USE OF THE SOFTWARE IN TERMS OF ITS CORRECTNESS,
29 
*                ACCURACY, RELIABILITY, OR OTHERWISE. THE ENTIRE RISK ARISING OUT OF USE
30 
*                OR PERFORMANCE OF THE SOFTWARE REMAINS WITH YOU. IN NO EVENT SHALL MTI,
31 
*                ITS AFFILIATED COMPANIES OR THEIR SUPPLIERS BE LIABLE FOR ANY DIRECT,
32 
*                INDIRECT, CONSEQUENTIAL, INCIDENTAL, OR SPECIAL DAMAGES (INCLUDING,
33 
*                WITHOUT LIMITATION, DAMAGES FOR LOSS OF PROFITS, BUSINESS INTERRUPTION,
34 
*                OR LOSS OF INFORMATION) ARISING OUT OF YOUR USE OF OR INABILITY TO USE
35 
*                THE SOFTWARE, EVEN IF MTI HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
36 
*                DAMAGES. Because some jurisdictions prohibit the exclusion or
37 
*                limitation of liability for consequential or incidental damages, the
38 
*                above limitation may not apply to you.
39 
*
40 
*                Copyright 2003 Micron Technology, Inc. All rights reserved.
41 
*
42 
* Rev  Author Date        Changes
43 
* ---  ------ ----------  ---------------------------------------
44 
* 2.1  SPH    03/19/2002  - Second Release
45 
*                         - Fix tWR and several incompatability
46 
*                           between different simulators
47 
* 3.0  TFK    02/18/2003  - Added tDSS and tDSH timing checks.
48 
*                         - Added tDQSH and tDQSL timing checks.
49 
* 3.1  CAH    05/28/2003  - update all models to release version 3.1
50 
*                           (no changes to this model)
51 
* 3.2  JMK    06/16/2003  - updated all DDR400 models to support CAS Latency 3
52 
* 3.3  JMK    09/11/2003  - Added initialization sequence checks.
53 
* 4.0  JMK    12/01/2003  - Grouped parameters into "ddr_parameters.v"
54 
*                         - Fixed tWTR check
55 
* 4.1  JMK    01/14/2004  - Grouped specify parameters by speed grade
56 
*                         - Fixed mem_sizes parameter
57 
* 4.2  JMK    03/19/2004  - Fixed pulse width checking on Dqs
58 
* 4.3  JMK    04/27/2004  - Changed BL wire size in tb module
59 
*                         - Changed Dq_buf size to [15:0]
60 
* 5.0  JMK    06/16/2004  - Added read to write checking.
61 
*                         - Added read with precharge truncation to write checking.
62 
*                         - Added associative memory array to reduce memory consumption.
63 
*                         - Added checking for required DQS edges during write.
64 
* 5.1  JMK    08/16/2004  - Fixed checking for required DQS edges during write.
65 
*                         - Fixed wdqs_valid window.
66 
* 5.2  JMK    09/24/2004  - Read or Write without activate will be ignored.
67 
* 5.3  JMK    10/27/2004  - Added tMRD checking during Auto Refresh and Activate.
68 
*                         - Added tRFC checking during Load Mode and Precharge.
69 
* 5.4  JMK    12/13/2004  - The model will not respond to illegal command sequences.
70 
* 5.5  SPH    01/13/2005  - The model will issue a halt on illegal command sequences.
71 
*      JMK    02/11/2005  - Changed the display format for numbers to hex.
72 
* 5.6  JMK    04/22/2005  - Fixed Write with auto precharge calculation.
73 
* 5.7  JMK    08/05/2005  - Changed conditions for read with precharge truncation error.
74 
*                         - Renamed parameters file with .vh extension.
75 
****************************************************************************************/
76 
 
77 
// DO NOT CHANGE THE TIMESCALE
78 
// MAKE SURE YOUR SIMULATOR USE "PS" RESOLUTION
79 
`timescale 1ns / 1ps
80 
 
81 
module ddr (Dq, Dqs, Addr, Ba, Clk, Clk_n, Cke, Cs_n, Ras_n, Cas_n, We_n, Dm);
82 
 
83 
    `include "ddr_parameters.vh"
84 
 
85 
    // Port Declarations
86 
    inout       [DQ_BITS - 1 : 0] Dq;
87 
    inout      [DQS_BITS - 1 : 0] Dqs;
88 
    input     [ADDR_BITS - 1 : 0] Addr;
89 
    input                 [1 : 0] Ba;
90 
    input                         Clk;
91 
    input                         Clk_n;
92 
    input                         Cke;
93 
    input                         Cs_n;
94 
    input                         Ras_n;
95 
    input                         Cas_n;
96 
    input                         We_n;
97 
    input       [DM_BITS - 1 : 0] Dm;
98 
 
99 
    // Internal Wires (fixed width)
100 
    wire                 [15 : 0] Dq_in;
101 
    wire                  [1 : 0] Dqs_in;
102 
    wire                  [1 : 0] Dm_in;
103 
 
104 
    assign Dq_in   [DQ_BITS - 1 : 0] = Dq;
105 
    assign Dqs_in [DQS_BITS - 1 : 0] = Dqs;
106 
    assign Dm_in   [DM_BITS - 1 : 0] = Dm;
107 
 
108 
    // Data pair
109 
    reg                  [15 : 0] dq_rise;
110 
    reg                   [1 : 0] dm_rise;
111 
    reg                  [15 : 0] dq_fall;
112 
    reg                   [1 : 0] dm_fall;
113 
    reg                   [3 : 0] dm_pair;
114 
    reg                  [15 : 0] Dq_buf;
115 
 
116 
    // Mode Register
117 
    reg       [ADDR_BITS - 1 : 0] Mode_reg;
118 
 
119 
    // Internal System Clock
120 
    reg                           CkeZ, Sys_clk;
121 
 
122 
    // Internal Dqs initialize
123 
    reg                           Dqs_int;
124 
 
125 
    // Dqs buffer
126 
    reg        [DQS_BITS - 1 : 0] Dqs_out;
127 
 
128 
    // Dq buffer
129 
    reg         [DQ_BITS - 1 : 0] Dq_out;
130 
 
131 
    // Read pipeline variables
132 
    reg                           Read_cmnd [0 : 6];
133 
    reg                   [1 : 0] Read_bank [0 : 6];
134 
    reg        [COL_BITS - 1 : 0] Read_cols [0 : 6];
135 
 
136 
    // Write pipeline variables
137 
    reg                           Write_cmnd [0 : 3];
138 
    reg                   [1 : 0] Write_bank [0 : 3];
139 
    reg        [COL_BITS - 1 : 0] Write_cols [0 : 3];
140 
 
141 
    // Auto precharge variables
142 
    reg                           Read_precharge  [0 : 3];
143 
    reg                           Write_precharge [0 : 3];
144 
    integer                       Count_precharge [0 : 3];
145 
 
146 
    // Manual precharge variables
147 
    reg                           A10_precharge  [0 : 6];
148 
    reg                   [1 : 0] Bank_precharge [0 : 6];
149 
    reg                           Cmnd_precharge [0 : 6];
150 
 
151 
    // Burst terminate variables
152 
    reg                           Cmnd_bst [0 : 6];
153 
 
154 
    // Memory Banks
155 
`ifdef FULL_MEM
156 
    reg         [DQ_BITS - 1 : 0] mem_array  [0 : (1<<full_mem_bits)-1];
157 
`else
158 
    reg         [DQ_BITS - 1 : 0] mem_array  [0 : (1<<part_mem_bits)-1];
159 
    reg   [full_mem_bits - 1 : 0] addr_array [0 : (1<<part_mem_bits)-1];
160 
    reg   [part_mem_bits     : 0] mem_used;
161 
    initial mem_used = 0;
162 
`endif
163 
 
164 
    // Dqs edge checking
165 
    integer i;
166 
    reg  [1:0] expect_pos_dqs;
167 
    reg  [1:0] expect_neg_dqs;
168 
 
169 
    // Burst counter
170 
    reg        [COL_BITS - 1 : 0] Burst_counter;
171 
 
172 
    // Precharge variables
173 
    reg                           Pc_b0, Pc_b1, Pc_b2, Pc_b3;
174 
 
175 
    // Activate variables
176 
    reg                           Act_b0, Act_b1, Act_b2, Act_b3;
177 
 
178 
    // Data IO variables
179 
    reg                           Data_in_enable;
180 
    reg                           Data_out_enable;
181 
 
182 
    // Internal address mux variables
183 
    reg                   [1 : 0] Prev_bank;
184 
    reg                   [1 : 0] Bank_addr;
185 
    reg        [COL_BITS - 1 : 0] Cols_addr, Cols_brst, Cols_temp;
186 
    reg       [ADDR_BITS - 1 : 0] Rows_addr;
187 
    reg       [ADDR_BITS - 1 : 0] B0_row_addr;
188 
    reg       [ADDR_BITS - 1 : 0] B1_row_addr;
189 
    reg       [ADDR_BITS - 1 : 0] B2_row_addr;
190 
    reg       [ADDR_BITS - 1 : 0] B3_row_addr;
191 
 
192 
    // DLL Reset variable
193 
    reg                           DLL_enable;
194 
    reg                           DLL_reset;
195 
    reg                           DLL_done;
196 
    integer                       DLL_count;
197 
    integer                       aref_count;
198 
    integer                       Prech_count;
199 
    reg                           power_up_done;
200 
 
201 
    // Write DQS for tDSS, tDSH, tDQSH, tDQSL checks
202 
    wire      wdqs_valid = Write_cmnd[2] || Write_cmnd[1] || Data_in_enable;
203 
 
204 
    // Commands Decode
205 
    wire      Active_enable   = ~Cs_n & ~Ras_n &  Cas_n &  We_n;
206 
    wire      Aref_enable     = ~Cs_n & ~Ras_n & ~Cas_n &  We_n;
207 
    wire      Burst_term      = ~Cs_n &  Ras_n &  Cas_n & ~We_n;
208 
    wire      Ext_mode_enable = ~Cs_n & ~Ras_n & ~Cas_n & ~We_n &  Ba[0] & ~Ba[1];
209 
    wire      Mode_reg_enable = ~Cs_n & ~Ras_n & ~Cas_n & ~We_n & ~Ba[0] & ~Ba[1];
210 
    wire      Prech_enable    = ~Cs_n & ~Ras_n &  Cas_n & ~We_n;
211 
    wire      Read_enable     = ~Cs_n &  Ras_n & ~Cas_n &  We_n;
212 
    wire      Write_enable    = ~Cs_n &  Ras_n & ~Cas_n & ~We_n;
213 
 
214 
    // Burst Length Decode
215 
    wire [3:0] burst_length = 1 << (Mode_reg[2:0]);
216 
    reg  [3:0] read_precharge_truncation;
217 
 
218 
    // CAS Latency Decode
219 
//    wire [2:0] cas_latency_x2 = (Mode_reg[6:4] === 3'o6) ? 5 : 2*Mode_reg[6:4];
220 
    wire [2:0] cas_latency_x2 = 5;
221 
 
222 
    // DQS Buffer
223 
    assign    Dqs = Dqs_out;
224 
 
225 
    // DQ Buffer
226 
    assign    Dq  = Dq_out;
227 
 
228 
    // Timing Check
229 
    time      MRD_chk;
230 
    time      RFC_chk;
231 
    time      RRD_chk;
232 
    time      RAS_chk0, RAS_chk1, RAS_chk2, RAS_chk3;
233 
    time      RAP_chk0, RAP_chk1, RAP_chk2, RAP_chk3;
234 
    time      RC_chk0, RC_chk1, RC_chk2, RC_chk3;
235 
    time      RCD_chk0, RCD_chk1, RCD_chk2, RCD_chk3;
236 
    time      RP_chk0, RP_chk1, RP_chk2, RP_chk3;
237 
    time      WR_chk0, WR_chk1, WR_chk2, WR_chk3;
238 
 
239 
    initial begin
240 
        CkeZ = 1'b0;
241 
        Sys_clk = 1'b0;
242 
        {Pc_b0, Pc_b1, Pc_b2, Pc_b3} = 4'b0000;
243 
        {Act_b0, Act_b1, Act_b2, Act_b3} = 4'b1111;
244 
        Dqs_int = 1'b0;
245 
        Dqs_out = {DQS_BITS{1'bz}};
246 
        Dq_out = {DQ_BITS{1'bz}};
247 
        Data_in_enable = 1'b0;
248 
        Data_out_enable = 1'b0;
249 
        DLL_enable = 1'b0;
250 
        DLL_reset = 1'b0;
251 
        DLL_done = 1'b0;
252 
        DLL_count = 0;
253 
        aref_count = 0;
254 
        Prech_count = 0;
255 
        power_up_done = 0;
256 
        MRD_chk = 0;
257 
        RFC_chk = 0;
258 
        RRD_chk = 0;
259 
        {RAS_chk0, RAS_chk1, RAS_chk2, RAS_chk3} = 0;
260 
        {RAP_chk0, RAP_chk1, RAP_chk2, RAP_chk3} = 0;
261 
        {RC_chk0, RC_chk1, RC_chk2, RC_chk3} = 0;
262 
        {RCD_chk0, RCD_chk1, RCD_chk2, RCD_chk3} = 0;
263 
        {RP_chk0, RP_chk1, RP_chk2, RP_chk3} = 0;
264 
        {WR_chk0, WR_chk1, WR_chk2, WR_chk3} = 0;
265 
        $timeformat (-9, 3, " ns", 12);
266 
    end
267 
 
268 
    // System Clock
269 
    always begin
270 
        @ (posedge Clk) begin
271 
            Sys_clk = CkeZ;
272 
            CkeZ = Cke;
273 
        end
274 
        @ (negedge Clk) begin
275 
            Sys_clk = 1'b0;
276 
        end
277 
    end
278 
 
279 
    // Check to make sure that we have a Deselect or NOP command on the bus when CKE is brought high
280 
    always @(Cke) begin
281 
        if (Cke === 1'b1) begin
282 
            if (!((Cs_n) || (~Cs_n &  Ras_n & Cas_n &  We_n))) begin
283 
                $display ("%m: at time %t MEMORY ERROR:  You must have a Deselect or NOP command applied", $time);
284 
                $display ("%m:           when the Clock Enable is brought High.");
285 
            end
286 
        end
287 
    end
288 
 
289 
    // Check the initialization sequence
290 
    initial begin
291 
        @ (posedge Cke) begin
292 
            @ (posedge DLL_enable) begin
293 
                aref_count = 0;
294 
                @ (posedge DLL_reset) begin
295 
                    @ (Prech_count) begin
296 
                        if (aref_count >= 2) begin
297 
                            if (Debug) $display ("%m: at time %t MEMORY:  Power Up and Initialization Sequence is complete", $time);
298 
                            power_up_done = 1;
299 
                        end else begin
300 
                            aref_count = 0;
301 
                            @ (aref_count >= 2) begin
302 
                                if (Debug) $display ("%m: at time %t MEMORY:  Power Up and Initialization Sequence is complete", $time);
303 
                                power_up_done = 1;
304 
                            end
305 
                        end
306 
                    end
307 
                end
308 
            end
309 
        end
310 
    end
311 
 
312 
    // Write Memory
313 
    task write_mem;
314 
        input [full_mem_bits - 1 : 0] addr;
315 
        input       [DQ_BITS - 1 : 0] data;
316 
        reg       [part_mem_bits : 0] i;
317 
        begin
318 
`ifdef FULL_MEM
319 
            mem_array[addr] = data;
320 
`else
321 
            begin : loop
322 
                for (i = 0; i < mem_used; i = i + 1) begin
323 
                    if (addr_array[i] === addr) begin
324 
                        disable loop;
325 
                    end
326 
                end
327 
            end
328 
            if (i === mem_used) begin
329 
                if (i === (1<<part_mem_bits)) begin
330 
                    $display ("At time %t ERROR: Memory overflow.\n  Write to Address %h with Data %h will be lost.\n  You must increase the part_mem_bits parameter or define FULL_MEM.", $time, addr, data);
331 
                end else begin
332 
                    mem_used = mem_used + 1;
333 
                    addr_array[i] = addr;
334 
                end
335 
            end
336 
            mem_array[i] = data;
337 
`endif
338 
        end
339 
    endtask
340 
 
341 
    // Read Memory
342 
    task read_mem;
343 
        input [full_mem_bits - 1 : 0] addr;
344 
        output      [DQ_BITS - 1 : 0] data;
345 
        reg       [part_mem_bits : 0] i;
346 
        begin
347 
`ifdef FULL_MEM
348 
            data = mem_array[addr];
349 
`else
350 
            begin : loop
351 
                for (i = 0; i < mem_used; i = i + 1) begin
352 
                    if (addr_array[i] === addr) begin
353 
                        disable loop;
354 
                    end
355 
                end
356 
            end
357 
            if (i <= mem_used) begin
358 
                data = mem_array[i];
359 
            end
360 
`endif
361 
        end
362 
    endtask
363 
 
364 
    // Burst Decode
365 
    task Burst_Decode;
366 
    begin
367 
 
368 
        // Advance Burst Counter
369 
        if (Burst_counter < burst_length) begin
370 
            Burst_counter = Burst_counter + 1;
371 
        end
372 
 
373 
        // Burst Type
374 
        if (Mode_reg[3] === 1'b0) begin                         // Sequential Burst
375 
            Cols_temp = Cols_addr + 1;
376 
        end else if (Mode_reg[3] === 1'b1) begin                // Interleaved Burst
377 
            Cols_temp[2] =  Burst_counter[2] ^ Cols_brst[2];
378 
            Cols_temp[1] =  Burst_counter[1] ^ Cols_brst[1];
379 
            Cols_temp[0] =  Burst_counter[0] ^ Cols_brst[0];
380 
        end
381 
 
382 
        // Burst Length
383 
        if (burst_length === 2) begin
384 
            Cols_addr [0] = Cols_temp [0];
385 
        end else if (burst_length === 4) begin
386 
            Cols_addr [1 : 0] = Cols_temp [1 : 0];
387 
        end else if (burst_length === 8) begin
388 
            Cols_addr [2 : 0] = Cols_temp [2 : 0];
389 
        end else begin
390 
            Cols_addr = Cols_temp;
391 
        end
392 
 
393 
        // Data Counter
394 
        if (Burst_counter >= burst_length) begin
395 
            Data_in_enable = 1'b0;
396 
            Data_out_enable = 1'b0;
397 
            read_precharge_truncation = 4'h0;
398 
        end
399 
 
400 
    end
401 
    endtask
402 
 
403 
    // Manual Precharge Pipeline
404 
    task Manual_Precharge_Pipeline;
405 
    begin
406 
        // A10 Precharge Pipeline
407 
        A10_precharge[0] = A10_precharge[1];
408 
        A10_precharge[1] = A10_precharge[2];
409 
        A10_precharge[2] = A10_precharge[3];
410 
        A10_precharge[3] = A10_precharge[4];
411 
        A10_precharge[4] = A10_precharge[5];
412 
        A10_precharge[5] = A10_precharge[6];
413 
        A10_precharge[6] = 1'b0;
414 
 
415 
        // Bank Precharge Pipeline
416 
        Bank_precharge[0] = Bank_precharge[1];
417 
        Bank_precharge[1] = Bank_precharge[2];
418 
        Bank_precharge[2] = Bank_precharge[3];
419 
        Bank_precharge[3] = Bank_precharge[4];
420 
        Bank_precharge[4] = Bank_precharge[5];
421 
        Bank_precharge[5] = Bank_precharge[6];
422 
        Bank_precharge[6] = 2'b0;
423 
 
424 
        // Command Precharge Pipeline
425 
        Cmnd_precharge[0] = Cmnd_precharge[1];
426 
        Cmnd_precharge[1] = Cmnd_precharge[2];
427 
        Cmnd_precharge[2] = Cmnd_precharge[3];
428 
        Cmnd_precharge[3] = Cmnd_precharge[4];
429 
        Cmnd_precharge[4] = Cmnd_precharge[5];
430 
        Cmnd_precharge[5] = Cmnd_precharge[6];
431 
        Cmnd_precharge[6] = 1'b0;
432 
 
433 
        // Terminate a Read if same bank or all banks
434 
        if (Cmnd_precharge[0] === 1'b1) begin
435 
            if (Bank_precharge[0] === Bank_addr || A10_precharge[0] === 1'b1) begin
436 
                if (Data_out_enable === 1'b1) begin
437 
                    Data_out_enable = 1'b0;
438 
                    read_precharge_truncation = 4'hF;
439 
                end
440 
            end
441 
        end
442 
    end
443 
    endtask
444 
 
445 
    // Burst Terminate Pipeline
446 
    task Burst_Terminate_Pipeline;
447 
    begin
448 
        // Command Precharge Pipeline
449 
        Cmnd_bst[0] = Cmnd_bst[1];
450 
        Cmnd_bst[1] = Cmnd_bst[2];
451 
        Cmnd_bst[2] = Cmnd_bst[3];
452 
        Cmnd_bst[3] = Cmnd_bst[4];
453 
        Cmnd_bst[4] = Cmnd_bst[5];
454 
        Cmnd_bst[5] = Cmnd_bst[6];
455 
        Cmnd_bst[6] = 1'b0;
456 
 
457 
        // Terminate a Read regardless of banks
458 
        if (Cmnd_bst[0] === 1'b1 && Data_out_enable === 1'b1) begin
459 
            Data_out_enable = 1'b0;
460 
        end
461 
    end
462 
    endtask
463 
 
464 
    // Dq and Dqs Drivers
465 
    task Dq_Dqs_Drivers;
466 
    begin
467 
        // read command pipeline
468 
        Read_cmnd [0] = Read_cmnd [1];
469 
        Read_cmnd [1] = Read_cmnd [2];
470 
        Read_cmnd [2] = Read_cmnd [3];
471 
        Read_cmnd [3] = Read_cmnd [4];
472 
        Read_cmnd [4] = Read_cmnd [5];
473 
        Read_cmnd [5] = Read_cmnd [6];
474 
        Read_cmnd [6] = 1'b0;
475 
 
476 
        // read bank pipeline
477 
        Read_bank [0] = Read_bank [1];
478 
        Read_bank [1] = Read_bank [2];
479 
        Read_bank [2] = Read_bank [3];
480 
        Read_bank [3] = Read_bank [4];
481 
        Read_bank [4] = Read_bank [5];
482 
        Read_bank [5] = Read_bank [6];
483 
        Read_bank [6] = 2'b0;
484 
 
485 
        // read column pipeline
486 
        Read_cols [0] = Read_cols [1];
487 
        Read_cols [1] = Read_cols [2];
488 
        Read_cols [2] = Read_cols [3];
489 
        Read_cols [3] = Read_cols [4];
490 
        Read_cols [4] = Read_cols [5];
491 
        Read_cols [5] = Read_cols [6];
492 
        Read_cols [6] = 0;
493 
 
494 
        // Initialize Read command
495 
        if (Read_cmnd [0] === 1'b1) begin
496 
            Data_out_enable = 1'b1;
497 
            Bank_addr = Read_bank [0];
498 
            Cols_addr = Read_cols [0];
499 
            Cols_brst = Cols_addr [2 : 0];
500 
            Burst_counter = 0;
501 
 
502 
            // Row Address Mux
503 
            case (Bank_addr)
504 
                2'd0    : Rows_addr = B0_row_addr;
505 
                2'd1    : Rows_addr = B1_row_addr;
506 
                2'd2    : Rows_addr = B2_row_addr;
507 
                2'd3    : Rows_addr = B3_row_addr;
508 
                default : $display ("At time %t ERROR: Invalid Bank Address", $time);
509 
            endcase
510 
        end
511 
 
512 
        // Toggle Dqs during Read command
513 
        if (Data_out_enable === 1'b1) begin
514 
            Dqs_int = 1'b0;
515 
            if (Dqs_out === {DQS_BITS{1'b0}}) begin
516 
                Dqs_out = {DQS_BITS{1'b1}};
517 
            end else if (Dqs_out === {DQS_BITS{1'b1}}) begin
518 
                Dqs_out = {DQS_BITS{1'b0}};
519 
            end else begin
520 
                Dqs_out = {DQS_BITS{1'b0}};
521 
            end
522 
        end else if (Data_out_enable === 1'b0 && Dqs_int === 1'b0) begin
523 
            Dqs_out = {DQS_BITS{1'bz}};
524 
        end
525 
 
526 
        // Initialize dqs for Read command
527 
        if (Read_cmnd [2] === 1'b1) begin
528 
            if (Data_out_enable === 1'b0) begin
529 
                Dqs_int = 1'b1;
530 
                Dqs_out = {DQS_BITS{1'b0}};
531 
            end
532 
        end
533 
 
534 
        // Read latch
535 
        if (Data_out_enable === 1'b1) begin
536 
            // output data
537 
            read_mem({Bank_addr, Rows_addr, Cols_addr}, Dq_out);
538 
            if (Debug) begin
539 
                $display ("At time %t READ : Bank = %h, Row = %h, Col = %h, Data = %h", $time, Bank_addr, Rows_addr, Cols_addr, Dq_out);
540 
            end
541 
        end else begin
542 
            Dq_out = {DQ_BITS{1'bz}};
543 
        end
544 
    end
545 
    endtask
546 
 
547 
    // Write FIFO and DM Mask Logic
548 
    task Write_FIFO_DM_Mask_Logic;
549 
    begin
550 
        // Write command pipeline
551 
        Write_cmnd [0] = Write_cmnd [1];
552 
        Write_cmnd [1] = Write_cmnd [2];
553 
        Write_cmnd [2] = Write_cmnd [3];
554 
        Write_cmnd [3] = 1'b0;
555 
 
556 
        // Write command pipeline
557 
        Write_bank [0] = Write_bank [1];
558 
        Write_bank [1] = Write_bank [2];
559 
        Write_bank [2] = Write_bank [3];
560 
        Write_bank [3] = 2'b0;
561 
 
562 
        // Write column pipeline
563 
        Write_cols [0] = Write_cols [1];
564 
        Write_cols [1] = Write_cols [2];
565 
        Write_cols [2] = Write_cols [3];
566 
        Write_cols [3] = {COL_BITS{1'b0}};
567 
 
568 
        // Initialize Write command
569 
        if (Write_cmnd [0] === 1'b1) begin
570 
            Data_in_enable = 1'b1;
571 
            Bank_addr = Write_bank [0];
572 
            Cols_addr = Write_cols [0];
573 
            Cols_brst = Cols_addr [2 : 0];
574 
            Burst_counter = 0;
575 
 
576 
            // Row address mux
577 
            case (Bank_addr)
578 
                2'd0    : Rows_addr = B0_row_addr;
579 
                2'd1    : Rows_addr = B1_row_addr;
580 
                2'd2    : Rows_addr = B2_row_addr;
581 
                2'd3    : Rows_addr = B3_row_addr;
582 
                default : $display ("At time %t ERROR: Invalid Row Address", $time);
583 
            endcase
584 
        end
585 
 
586 
        // Write data
587 
        if (Data_in_enable === 1'b1) begin
588 
 
589 
            // Data Buffer
590 
            read_mem({Bank_addr, Rows_addr, Cols_addr}, Dq_buf);
591 
 
592 
            // write negedge Dqs on posedge Sys_clk
593 
            if (Sys_clk) begin
594 
                if (!dm_fall[0]) begin
595 
                    Dq_buf [ 7 : 0] = dq_fall [ 7 : 0];
596 
                end
597 
                if (!dm_fall[1]) begin
598 
                    Dq_buf [15 : 8] = dq_fall [15 : 8];
599 
                end
600 
                if (~&dm_fall) begin
601 
                    if (Debug) begin
602 
                        $display ("At time %t WRITE: Bank = %h, Row = %h, Col = %h, Data = %h", $time, Bank_addr, Rows_addr, Cols_addr, Dq_buf[DQ_BITS-1:0]);
603 
                    end
604 
                end
605 
            // write posedge Dqs on negedge Sys_clk
606 
            end else begin
607 
                if (!dm_rise[0]) begin
608 
                    Dq_buf [ 7 : 0] = dq_rise [ 7 : 0];
609 
                end
610 
                if (!dm_rise[1]) begin
611 
                    Dq_buf [15 : 8] = dq_rise [15 : 8];
612 
                end
613 
                if (~&dm_rise) begin
614 
                    if (Debug) begin
615 
                        $display ("At time %t WRITE: Bank = %h, Row = %h, Col = %h, Data = %h", $time, Bank_addr, Rows_addr, Cols_addr, Dq_buf[DQ_BITS-1:0]);
616 
                    end
617 
                end
618 
            end
619 
 
620 
            // Write Data
621 
            write_mem({Bank_addr, Rows_addr, Cols_addr}, Dq_buf);
622 
 
623 
            // tWR start and tWTR check
624 
            if (Sys_clk && &dm_pair === 1'b0)  begin
625 
                case (Bank_addr)
626 
                    2'd0    : WR_chk0 = $time;
627 
                    2'd1    : WR_chk1 = $time;
628 
                    2'd2    : WR_chk2 = $time;
629 
                    2'd3    : WR_chk3 = $time;
630 
                    default : $display ("At time %t ERROR: Invalid Bank Address (tWR)", $time);
631 
                endcase
632 
 
633 
                // tWTR check
634 
                if (Read_enable === 1'b1) begin
635 
                    $display ("At time %t ERROR: tWTR violation during Read", $time);
636 
                end
637 
            end
638 
        end
639 
    end
640 
    endtask
641 
 
642 
    // Auto Precharge Calculation
643 
    task Auto_Precharge_Calculation;
644 
    begin
645 
        // Precharge counter
646 
        if (Read_precharge [0] === 1'b1 || Write_precharge [0] === 1'b1) begin
647 
            Count_precharge [0] = Count_precharge [0] + 1;
648 
        end
649 
        if (Read_precharge [1] === 1'b1 || Write_precharge [1] === 1'b1) begin
650 
            Count_precharge [1] = Count_precharge [1] + 1;
651 
        end
652 
        if (Read_precharge [2] === 1'b1 || Write_precharge [2] === 1'b1) begin
653 
            Count_precharge [2] = Count_precharge [2] + 1;
654 
        end
655 
        if (Read_precharge [3] === 1'b1 || Write_precharge [3] === 1'b1) begin
656 
            Count_precharge [3] = Count_precharge [3] + 1;
657 
        end
658 
 
659 
        // Read with AutoPrecharge Calculation
660 
        //      The device start internal precharge when:
661 
        //          1.  Meet tRAS requirement
662 
        //          2.  BL/2 cycles after command
663 
        if ((Read_precharge[0] === 1'b1) && ($time - RAS_chk0 >= tRAS)) begin
664 
            if (Count_precharge[0] >= burst_length/2) begin
665 
                Pc_b0 = 1'b1;
666 
                Act_b0 = 1'b0;
667 
                RP_chk0 = $time;
668 
                Read_precharge[0] = 1'b0;
669 
            end
670 
        end
671 
        if ((Read_precharge[1] === 1'b1) && ($time - RAS_chk1 >= tRAS)) begin
672 
            if (Count_precharge[1] >= burst_length/2) begin
673 
                Pc_b1 = 1'b1;
674 
                Act_b1 = 1'b0;
675 
                RP_chk1 = $time;
676 
                Read_precharge[1] = 1'b0;
677 
            end
678 
        end
679 
        if ((Read_precharge[2] === 1'b1) && ($time - RAS_chk2 >= tRAS)) begin
680 
            if (Count_precharge[2] >= burst_length/2) begin
681 
                Pc_b2 = 1'b1;
682 
                Act_b2 = 1'b0;
683 
                RP_chk2 = $time;
684 
                Read_precharge[2] = 1'b0;
685 
            end
686 
        end
687 
        if ((Read_precharge[3] === 1'b1) && ($time - RAS_chk3 >= tRAS)) begin
688 
            if (Count_precharge[3] >= burst_length/2) begin
689 
                Pc_b3 = 1'b1;
690 
                Act_b3 = 1'b0;
691 
                RP_chk3 = $time;
692 
                Read_precharge[3] = 1'b0;
693 
            end
694 
        end
695 
 
696 
        // Write with AutoPrecharge Calculation
697 
        //      The device start internal precharge when:
698 
        //          1.  Meet tRAS requirement
699 
        //          2.  Write Latency PLUS BL/2 cycles PLUS tWR after Write command
700 
 
701 
        if ((Write_precharge[0] === 1'b1) && ($time - RAS_chk0 >= tRAS)) begin
702 
            if ((Count_precharge[0] >= burst_length/2+1) && ($time - WR_chk0 >= tWR)) begin
703 
                Pc_b0 = 1'b1;
704 
                Act_b0 = 1'b0;
705 
                RP_chk0 = $time;
706 
                Write_precharge[0] = 1'b0;
707 
            end
708 
        end
709 
        if ((Write_precharge[1] === 1'b1) && ($time - RAS_chk1 >= tRAS)) begin
710 
            if ((Count_precharge[1] >= burst_length/2+1) && ($time - WR_chk1 >= tWR)) begin
711 
                Pc_b1 = 1'b1;
712 
                Act_b1 = 1'b0;
713 
                RP_chk1 = $time;
714 
                Write_precharge[1] = 1'b0;
715 
            end
716 
        end
717 
        if ((Write_precharge[2] === 1'b1) && ($time - RAS_chk2 >= tRAS)) begin
718 
            if ((Count_precharge[2] >= burst_length/2+1) && ($time - WR_chk2 >= tWR)) begin
719 
                Pc_b2 = 1'b1;
720 
                Act_b2 = 1'b0;
721 
                RP_chk2 = $time;
722 
                Write_precharge[2] = 1'b0;
723 
            end
724 
        end
725 
        if ((Write_precharge[3] === 1'b1) && ($time - RAS_chk3 >= tRAS)) begin
726 
            if ((Count_precharge[3] >= burst_length/2+1) && ($time - WR_chk3 >= tWR)) begin
727 
                Pc_b3 = 1'b1;
728 
                Act_b3 = 1'b0;
729 
                RP_chk3 = $time;
730 
                Write_precharge[3] = 1'b0;
731 
            end
732 
        end
733 
    end
734 
    endtask
735 
 
736 
    // DLL Counter
737 
    task DLL_Counter;
738 
    begin
739 
        if (DLL_reset === 1'b1 && DLL_done === 1'b0) begin
740 
            DLL_count = DLL_count + 1;
741 
            if (DLL_count >= 200) begin
742 
                DLL_done = 1'b1;
743 
            end
744 
        end
745 
    end
746 
    endtask
747 
 
748 
    // Control Logic
749 
    task Control_Logic;
750 
    begin
751 
        // Auto Refresh
752 
        if (Aref_enable === 1'b1) begin
753 
            // Display Debug Message
754 
            if (Debug) begin
755 
                $display ("At time %t AREF : Auto Refresh", $time);
756 
            end
757 
 
758 
            // Precharge to Auto Refresh
759 
            if (($time - RP_chk0 < tRP) || ($time - RP_chk1 < tRP) ||
760 
                ($time - RP_chk2 < tRP) || ($time - RP_chk3 < tRP)) begin
761 
                $display ("At time %t ERROR: tRP violation during Auto Refresh", $time);
762 
            end
763 
 
764 
            // LMR/EMR to Auto Refresh
765 
            if ($time - MRD_chk < tMRD) begin
766 
                $display ("At time %t ERROR: tMRD violation during Auto Refresh", $time);
767 
            end
768 
 
769 
            // Auto Refresh to Auto Refresh
770 
            if ($time - RFC_chk < tRFC) begin
771 
                $display ("At time %t ERROR: tRFC violation during Auto Refresh", $time);
772 
            end
773 
 
774 
            // Precharge to Auto Refresh
775 
            if (Pc_b0 === 1'b0 || Pc_b1 === 1'b0 || Pc_b2 === 1'b0 || Pc_b3 === 1'b0) begin
776 
                $display ("At time %t ERROR: All banks must be Precharged before Auto Refresh", $time);
777 
                if (!no_halt) $stop (0);
778 
            end else begin
779 
                aref_count = aref_count + 1;
780 
                RFC_chk = $time;
781 
            end
782 
        end
783 
 
784 
        // Extended Mode Register
785 
        if (Ext_mode_enable === 1'b1) begin
786 
            if (Debug) begin
787 
                $display ("At time %t EMR  : Extended Mode Register", $time);
788 
            end
789 
 
790 
            // Precharge to LMR/EMR
791 
            if (($time - RP_chk0 < tRP) || ($time - RP_chk1 < tRP) ||
792 
                ($time - RP_chk2 < tRP) || ($time - RP_chk3 < tRP)) begin
793 
                $display ("At time %t ERROR: tRP violation during Extended Mode Register", $time);
794 
            end
795 
 
796 
            // LMR/EMR to LMR/EMR
797 
            if ($time - MRD_chk < tMRD) begin
798 
                $display ("At time %t ERROR: tMRD violation during Extended Mode Register", $time);
799 
            end
800 
 
801 
            // Auto Refresh to LMR/EMR
802 
            if ($time - RFC_chk < tRFC) begin
803 
                $display ("At time %t ERROR: tRFC violation during Extended Mode Register", $time);
804 
            end
805 
 
806 
            // Precharge to LMR/EMR
807 
            if (Pc_b0 === 1'b0 || Pc_b1 === 1'b0 || Pc_b2 === 1'b0 || Pc_b3 === 1'b0) begin
808 
                $display ("At time %t ERROR: all banks must be Precharged before Extended Mode Register", $time);
809 
                if (!no_halt) $stop (0);
810 
            end else begin
811 
                if (Addr[0] === 1'b0) begin
812 
                    DLL_enable = 1'b1;
813 
                    if (Debug) begin
814 
                        $display ("At time %t EMR  : Enable DLL", $time);
815 
                    end
816 
                end else begin
817 
                    DLL_enable = 1'b0;
818 
                    if (Debug) begin
819 
                        $display ("At time %t EMR  : Disable DLL", $time);
820 
                    end
821 
                end
822 
                MRD_chk = $time;
823 
            end
824 
        end
825 
 
826 
        // Load Mode Register
827 
        if (Mode_reg_enable === 1'b1) begin
828 
            if (Debug) begin
829 
                $display ("At time %t LMR  : Load Mode Register", $time);
830 
            end
831 
 
832 
            // Precharge to LMR/EMR
833 
            if (($time - RP_chk0 < tRP) || ($time - RP_chk1 < tRP) ||
834 
                ($time - RP_chk2 < tRP) || ($time - RP_chk3 < tRP)) begin
835 
                $display ("At time %t ERROR: tRP violation during Load Mode Register", $time);
836 
            end
837 
 
838 
            // LMR/EMR to LMR/EMR
839 
            if ($time - MRD_chk < tMRD) begin
840 
                $display ("At time %t ERROR: tMRD violation during Load Mode Register", $time);
841 
            end
842 
 
843 
            // Auto Refresh to LMR/EMR
844 
            if ($time - RFC_chk < tRFC) begin
845 
                $display ("At time %t ERROR: tRFC violation during Load Mode Register", $time);
846 
            end
847 
 
848 
            // Precharge to LMR/EMR
849 
            if (Pc_b0 === 1'b0 || Pc_b1 === 1'b0 || Pc_b2 === 1'b0 || Pc_b3 === 1'b0) begin
850 
                $display ("At time %t ERROR: all banks must be Precharged before Load Mode Register", $time);
851 
            end else begin
852 
                // Register Mode
853 
                Mode_reg = Addr;
854 
 
855 
                // DLL Reset
856 
                if (DLL_enable === 1'b1 && Addr [8] === 1'b1) begin
857 
                    DLL_reset = 1'b1;
858 
                    DLL_done = 1'b0;
859 
                    DLL_count = 0;
860 
                end else if (DLL_enable === 1'b1 && DLL_reset === 1'b0 && Addr [8] === 1'b0) begin
861 
                    $display ("At time %t ERROR: DLL is ENABLE: DLL RESET is required.", $time);
862 
                end else if (DLL_enable === 1'b0 && Addr [8] === 1'b1) begin
863 
                    $display ("At time %t ERROR: DLL is DISABLE: DLL RESET will be ignored.", $time);
864 
                end
865 
 
866 
                // Burst Length
867 
                case (Addr [2 : 0])
868 
                    3'b001  : $display ("At time %t LMR  : Burst Length = 2", $time);
869 
                    3'b010  : $display ("At time %t LMR  : Burst Length = 4", $time);
870 
                    3'b011  : $display ("At time %t LMR  : Burst Length = 8", $time);
871 
                    default : $display ("At time %t ERROR: Burst Length not supported", $time);
872 
                endcase
873 
 
874 
                // CAS Latency
875 
                case (Addr [6 : 4])
876 
                    3'b010  : $display ("At time %t LMR  : CAS Latency = 2", $time);
877 
                    3'b110  : $display ("At time %t LMR  : CAS Latency = 2.5", $time);
878 
                    3'b011  : $display ("At time %t LMR  : CAS Latency = 3", $time);
879 
                    default : $display ("At time %t ERROR: CAS Latency not supported", $time);
880 
                endcase
881 
 
882 
                // Record current tMRD time
883 
                MRD_chk = $time;
884 
            end
885 
        end
886 
 
887 
        // Activate Block
888 
        if (Active_enable === 1'b1) begin
889 
            if (!(power_up_done)) begin
890 
                $display ("%m: at time %t ERROR: Power Up and Initialization Sequence not completed before executing Activate command", $time);
891 
            end
892 
            // Display Debug Message
893 
            if (Debug) begin
894 
                $display ("At time %t ACT  : Bank = %h, Row = %h", $time, Ba, Addr);
895 
            end
896 
 
897 
            // Activate to Activate (different bank)
898 
            if ((Prev_bank != Ba) && ($time - RRD_chk < tRRD)) begin
899 
                $display ("At time %t ERROR: tRRD violation during Activate bank %h", $time, Ba);
900 
            end
901 
 
902 
            // LMR/EMR to Activate
903 
            if ($time - MRD_chk < tMRD) begin
904 
                $display ("At time %t ERROR: tMRD violation during Activate bank %h", $time, Ba);
905 
            end
906 
 
907 
            // AutoRefresh to Activate
908 
            if ($time - RFC_chk < tRFC) begin
909 
                $display ("At time %t ERROR: tRFC violation during Activate bank %h", $time, Ba);
910 
            end
911 
 
912 
            // Precharge to Activate
913 
            if ((Ba === 2'b00 && Pc_b0  === 1'b0) || (Ba === 2'b01 && Pc_b1  === 1'b0) ||
914 
                (Ba === 2'b10 && Pc_b2  === 1'b0) || (Ba === 2'b11 && Pc_b3  === 1'b0)) begin
915 
                $display ("At time %t ERROR: Bank = %h is already activated - Command Ignored", $time, Ba);
916 
                if (!no_halt) $stop (0);
917 
            end else begin
918 
                // Activate Bank 0
919 
                if (Ba === 2'b00 && Pc_b0 === 1'b1) begin
920 
                    // Activate to Activate (same bank)
921 
                    if ($time - RC_chk0 < tRC) begin
922 
                        $display ("At time %t ERROR: tRC violation during Activate bank %h", $time, Ba);
923 
                    end
924 
 
925 
                    // Precharge to Activate
926 
                    if ($time - RP_chk0 < tRP) begin
927 
                        $display ("At time %t ERROR: tRP violation during Activate bank %h", $time, Ba);
928 
                    end
929 
 
930 
                    // Record variables for checking violation
931 
                    Act_b0 = 1'b1;
932 
                    Pc_b0 = 1'b0;
933 
                    B0_row_addr = Addr;
934 
                    RC_chk0  = $time;
935 
                    RCD_chk0 = $time;
936 
                    RAS_chk0 = $time;
937 
                    RAP_chk0 = $time;
938 
                end
939 
 
940 
                // Activate Bank 1
941 
                if (Ba === 2'b01 && Pc_b1 === 1'b1) begin
942 
                    // Activate to Activate (same bank)
943 
                    if ($time - RC_chk1 < tRC) begin
944 
                        $display ("At time %t ERROR: tRC violation during Activate bank %h", $time, Ba);
945 
                    end
946 
 
947 
                    // Precharge to Activate
948 
                    if ($time - RP_chk1 < tRP) begin
949 
                        $display ("At time %t ERROR: tRP violation during Activate bank %h", $time, Ba);
950 
                    end
951 
 
952 
                    // Record variables for checking violation
953 
                    Act_b1 = 1'b1;
954 
                    Pc_b1 = 1'b0;
955 
                    B1_row_addr = Addr;
956 
                    RC_chk1  = $time;
957 
                    RCD_chk1 = $time;
958 
                    RAS_chk1 = $time;
959 
                    RAP_chk1 = $time;
960 
                end
961 
 
962 
                // Activate Bank 2
963 
                if (Ba === 2'b10 && Pc_b2 === 1'b1) begin
964 
                    // Activate to Activate (same bank)
965 
                    if ($time - RC_chk2 < tRC) begin
966 
                        $display ("At time %t ERROR: tRC violation during Activate bank %h", $time, Ba);
967 
                    end
968 
 
969 
                    // Precharge to Activate
970 
                    if ($time - RP_chk2 < tRP) begin
971 
                        $display ("At time %t ERROR: tRP violation during Activate bank %h", $time, Ba);
972 
                    end
973 
 
974 
                    // Record variables for checking violation
975 
                    Act_b2 = 1'b1;
976 
                    Pc_b2 = 1'b0;
977 
                    B2_row_addr = Addr;
978 
                    RC_chk2  = $time;
979 
                    RCD_chk2 = $time;
980 
                    RAS_chk2 = $time;
981 
                    RAP_chk2 = $time;
982 
                end
983 
 
984 
                // Activate Bank 3
985 
                if (Ba === 2'b11 && Pc_b3 === 1'b1) begin
986 
                    // Activate to Activate (same bank)
987 
                    if ($time - RC_chk3 < tRC) begin
988 
                        $display ("At time %t ERROR: tRC violation during Activate bank %h", $time, Ba);
989 
                    end
990 
 
991 
                    // Precharge to Activate
992 
                    if ($time - RP_chk3 < tRP) begin
993 
                        $display ("At time %t ERROR: tRP violation during Activate bank %h", $time, Ba);
994 
                    end
995 
 
996 
                    // Record variables for checking violation
997 
                    Act_b3 = 1'b1;
998 
                    Pc_b3 = 1'b0;
999 
                    B3_row_addr = Addr;
1000 
                    RC_chk3  = $time;
1001 
                    RCD_chk3 = $time;
1002 
                    RAS_chk3 = $time;
1003 
                    RAP_chk3 = $time;
1004 
                end
1005 
                // Record variable for checking violation
1006 
                RRD_chk = $time;
1007 
                Prev_bank = Ba;
1008 
                read_precharge_truncation[Ba] = 1'b0;
1009 
            end
1010 
        end
1011 
 
1012 
        // Precharge Block - consider NOP if bank already precharged or in process of precharging
1013 
        if (Prech_enable === 1'b1) begin
1014 
            // Display Debug Message
1015 
            if (Debug) begin
1016 
                $display ("At time %t PRE  : Addr[10] = %b, Bank = %b", $time, Addr[10], Ba);
1017 
            end
1018 
 
1019 
            // LMR/EMR to Precharge
1020 
            if ($time - MRD_chk < tMRD) begin
1021 
                $display ("At time %t ERROR: tMRD violation during Precharge", $time);
1022 
            end
1023 
 
1024 
            // AutoRefresh to Precharge
1025 
            if ($time - RFC_chk < tRFC) begin
1026 
                $display ("At time %t ERROR: tRFC violation during Precharge", $time);
1027 
            end
1028 
 
1029 
            // Precharge bank 0
1030 
            if ((Addr[10] === 1'b1 || (Addr[10] === 1'b0 && Ba === 2'b00)) && Act_b0 === 1'b1) begin
1031 
                Act_b0 = 1'b0;
1032 
                Pc_b0 = 1'b1;
1033 
                RP_chk0 = $time;
1034 
 
1035 
                // Activate to Precharge Bank
1036 
                if ($time - RAS_chk0 < tRAS) begin
1037 
                    $display ("At time %t ERROR: tRAS violation during Precharge", $time);
1038 
                end
1039 
 
1040 
                // tWR violation check for Write
1041 
                if ($time - WR_chk0 < tWR) begin
1042 
                    $display ("At time %t ERROR: tWR violation during Precharge", $time);
1043 
                end
1044 
            end
1045 
 
1046 
            // Precharge bank 1
1047 
            if ((Addr[10] === 1'b1 || (Addr[10] === 1'b0 && Ba === 2'b01)) && Act_b1 === 1'b1) begin
1048 
                Act_b1 = 1'b0;
1049 
                Pc_b1 = 1'b1;
1050 
                RP_chk1 = $time;
1051 
 
1052 
                // Activate to Precharge Bank 1
1053 
                if ($time - RAS_chk1 < tRAS) begin
1054 
                    $display ("At time %t ERROR: tRAS violation during Precharge", $time);
1055 
                end
1056 
 
1057 
                // tWR violation check for Write
1058 
                if ($time - WR_chk1 < tWR) begin
1059 
                    $display ("At time %t ERROR: tWR violation during Precharge", $time);
1060 
                end
1061 
            end
1062 
 
1063 
            // Precharge bank 2
1064 
            if ((Addr[10] === 1'b1 || (Addr[10] === 1'b0 && Ba === 2'b10)) && Act_b2 === 1'b1) begin
1065 
                Act_b2 = 1'b0;
1066 
                Pc_b2 = 1'b1;
1067 
                RP_chk2 = $time;
1068 
 
1069 
                // Activate to Precharge Bank 2
1070 
                if ($time - RAS_chk2 < tRAS) begin
1071 
                    $display ("At time %t ERROR: tRAS violation during Precharge", $time);
1072 
                end
1073 
 
1074 
                // tWR violation check for Write
1075 
                if ($time - WR_chk2 < tWR) begin
1076 
                    $display ("At time %t ERROR: tWR violation during Precharge", $time);
1077 
                end
1078 
            end
1079 
 
1080 
            // Precharge bank 3
1081 
            if ((Addr[10] === 1'b1 || (Addr[10] === 1'b0 && Ba === 2'b11)) && Act_b3 === 1'b1) begin
1082 
                Act_b3 = 1'b0;
1083 
                Pc_b3 = 1'b1;
1084 
                RP_chk3 = $time;
1085 
 
1086 
                // Activate to Precharge Bank 3
1087 
                if ($time - RAS_chk3 < tRAS) begin
1088 
                    $display ("At time %t ERROR: tRAS violation during Precharge", $time);
1089 
                end
1090 
 
1091 
                // tWR violation check for Write
1092 
                if ($time - WR_chk3 < tWR) begin
1093 
                    $display ("At time %t ERROR: tWR violation during Precharge", $time);
1094 
                end
1095 
            end
1096 
 
1097 
            // Prech_count is to make sure we have met part of the initialization sequence
1098 
            Prech_count = Prech_count + 1;
1099 
 
1100 
            // Pipeline for READ
1101 
            A10_precharge [cas_latency_x2] = Addr[10];
1102 
            Bank_precharge[cas_latency_x2] = Ba;
1103 
            Cmnd_precharge[cas_latency_x2] = 1'b1;
1104 
        end
1105 
 
1106 
        // Burst terminate
1107 
        if (Burst_term === 1'b1) begin
1108 
            // Display Debug Message
1109 
            if (Debug) begin
1110 
                $display ("At time %t BST  : Burst Terminate",$time);
1111 
            end
1112 
 
1113 
            if (Data_in_enable === 1'b1) begin
1114 
                // Illegal to burst terminate a Write
1115 
                $display ("At time %t ERROR: It's illegal to burst terminate a Write", $time);
1116 
                if (!no_halt) $stop (0);
1117 
            end else if (Read_precharge[0] === 1'b1 || Read_precharge[1] === 1'b1 ||
1118 
                // Illegal to burst terminate a Read with Auto Precharge
1119 
                Read_precharge[2] === 1'b1 || Read_precharge[3] === 1'b1) begin
1120 
                $display ("At time %t ERROR: It's illegal to burst terminate a Read with Auto Precharge", $time);
1121 
                if (!no_halt) $stop (0);
1122 
            end else begin
1123 
                // Burst Terminate Command Pipeline for Read
1124 
                Cmnd_bst[cas_latency_x2] = 1'b1;
1125 
            end
1126 
 
1127 
        end
1128 
 
1129 
        // Read Command
1130 
        if (Read_enable === 1'b1) begin
1131 
            if (!(power_up_done)) begin
1132 
                $display ("%m: at time %t ERROR: Power Up and Initialization Sequence not completed before executing Read Command", $time);
1133 
            end
1134 
            // Check for DLL reset before Read
1135 
            if (DLL_reset === 1 && DLL_done === 0) begin
1136 
                $display ("%m: at time %t ERROR: You need to wait 200 tCK after DLL Reset Enable to Read, Not %0d clocks.", $time, DLL_count);
1137 
            end
1138 
            // Display Debug Message
1139 
            if (Debug) begin
1140 
                $display ("At time %t READ : Bank = %h, Col = %h", $time, Ba, {Addr [11], Addr [9 : 0]});
1141 
            end
1142 
 
1143 
            // Terminate a Write
1144 
            if (Data_in_enable === 1'b1) begin
1145 
                Data_in_enable = 1'b0;
1146 
            end
1147 
 
1148 
            // Activate to Read without Auto Precharge
1149 
            if ((Addr [10] === 1'b0 && Ba === 2'b00 && $time - RCD_chk0 < tRCD) ||
1150 
                (Addr [10] === 1'b0 && Ba === 2'b01 && $time - RCD_chk1 < tRCD) ||
1151 
                (Addr [10] === 1'b0 && Ba === 2'b10 && $time - RCD_chk2 < tRCD) ||
1152 
                (Addr [10] === 1'b0 && Ba === 2'b11 && $time - RCD_chk3 < tRCD)) begin
1153 
                $display("At time %t ERROR: tRCD violation during Read", $time);
1154 
            end
1155 
 
1156 
            // Activate to Read with Auto Precharge
1157 
            if ((Addr [10] === 1'b1 && Ba === 2'b00 && $time - RAP_chk0 < tRAP) ||
1158 
                (Addr [10] === 1'b1 && Ba === 2'b01 && $time - RAP_chk1 < tRAP) ||
1159 
                (Addr [10] === 1'b1 && Ba === 2'b10 && $time - RAP_chk2 < tRAP) ||
1160 
                (Addr [10] === 1'b1 && Ba === 2'b11 && $time - RAP_chk3 < tRAP)) begin
1161 
                $display ("At time %t ERROR: tRAP violation during Read", $time);
1162 
            end
1163 
 
1164 
            // Interrupt a Read with Auto Precharge (same bank only)
1165 
            if (Read_precharge [Ba] === 1'b1) begin
1166 
                $display ("At time %t ERROR: It's illegal to interrupt a Read with Auto Precharge", $time);
1167 
                if (!no_halt) $stop (0);
1168 
                // Cancel Auto Precharge
1169 
                if (Addr[10] === 1'b0) begin
1170 
                    Read_precharge [Ba]= 1'b0;
1171 
                end
1172 
            end
1173 
            // Activate to Read
1174 
            if ((Ba === 2'b00 && Pc_b0 === 1'b1) || (Ba === 2'b01 && Pc_b1 === 1'b1) ||
1175 
                (Ba === 2'b10 && Pc_b2 === 1'b1) || (Ba === 2'b11 && Pc_b3 === 1'b1)) begin
1176 
                $display("At time %t ERROR: Bank is not Activated for Read", $time);
1177 
                if (!no_halt) $stop (0);
1178 
            end else begin
1179 
                // CAS Latency pipeline
1180 
                Read_cmnd[cas_latency_x2] = 1'b1;
1181 
                Read_bank[cas_latency_x2] = Ba;
1182 
                Read_cols[cas_latency_x2] = {Addr [ADDR_BITS - 1 : 11], Addr [9 : 0]};
1183 
                // Auto Precharge
1184 
                if (Addr[10] === 1'b1) begin
1185 
                    Read_precharge [Ba]= 1'b1;
1186 
                    Count_precharge [Ba]= 0;
1187 
                end
1188 
            end
1189 
        end
1190 
 
1191 
        // Write Command
1192 
        if (Write_enable === 1'b1) begin
1193 
            if (!(power_up_done)) begin
1194 
                $display ("%m: at time %t ERROR: Power Up and Initialization Sequence not completed before executing Write Command", $time);
1195 
                if (!no_halt) $stop (0);
1196 
            end
1197 
            // display debug message
1198 
            if (Debug) begin
1199 
                $display ("At time %t WRITE: Bank = %h, Col = %h", $time, Ba, {Addr [ADDR_BITS - 1 : 11], Addr [9 : 0]});
1200 
            end
1201 
 
1202 
            // Activate to Write
1203 
            if ((Ba === 2'b00 && $time - RCD_chk0 < tRCD) ||
1204 
                (Ba === 2'b01 && $time - RCD_chk1 < tRCD) ||
1205 
                (Ba === 2'b10 && $time - RCD_chk2 < tRCD) ||
1206 
                (Ba === 2'b11 && $time - RCD_chk3 < tRCD)) begin
1207 
                $display("At time %t ERROR: tRCD violation during Write to Bank %h", $time, Ba);
1208 
            end
1209 
 
1210 
            // Read to Write
1211 
            if (Read_cmnd[0] || Read_cmnd[1] || Read_cmnd[2] || Read_cmnd[3] ||
1212 
                Read_cmnd[4] || Read_cmnd[5] || Read_cmnd[6] || (Burst_counter < burst_length)) begin
1213 
                if (Data_out_enable || read_precharge_truncation[Ba]) begin
1214 
                    $display("At time %t ERROR: Read to Write violation", $time);
1215 
                end
1216 
            end
1217 
 
1218 
            // Interrupt a Write with Auto Precharge (same bank only)
1219 
            if (Write_precharge [Ba] === 1'b1) begin
1220 
                $display ("At time %t ERROR: it's illegal to interrupt a Write with Auto Precharge", $time);
1221 
                if (!no_halt) $stop (0);
1222 
                // Cancel Auto Precharge
1223 
                if (Addr[10] === 1'b0) begin
1224 
                    Write_precharge [Ba]= 1'b0;
1225 
                end
1226 
            end
1227 
            // Activate to Write
1228 
            if ((Ba === 2'b00 && Pc_b0 === 1'b1) || (Ba === 2'b01 && Pc_b1 === 1'b1) ||
1229 
                (Ba === 2'b10 && Pc_b2 === 1'b1) || (Ba === 2'b11 && Pc_b3 === 1'b1)) begin
1230 
                $display("At time %t ERROR: Bank is not Activated for Write", $time);
1231 
                if (!no_halt) $stop (0);
1232 
            end else begin
1233 
                // Pipeline for Write
1234 
                Write_cmnd [3] = 1'b1;
1235 
                Write_bank [3] = Ba;
1236 
                Write_cols [3] = {Addr [ADDR_BITS - 1 : 11], Addr [9 : 0]};
1237 
                // Auto Precharge
1238 
                if (Addr[10] === 1'b1) begin
1239 
                    Write_precharge [Ba]= 1'b1;
1240 
                    Count_precharge [Ba]= 0;
1241 
                end
1242 
            end
1243 
        end
1244 
    end
1245 
    endtask
1246 
 
1247 
    task check_neg_dqs;
1248 
    begin
1249 
        if (Write_cmnd[2] || Write_cmnd[1] || Data_in_enable) begin
1250 
            for (i=0; i<DQS_BITS; i=i+1) begin
1251 
                if (expect_neg_dqs[i]) begin
1252 
                    $display ("At time %t ERROR: Negative DQS[%1d] transition required.", $time, i);
1253 
                end
1254 
                expect_neg_dqs[i] = 1'b1;
1255 
            end
1256 
        end else begin
1257 
            expect_pos_dqs = 0;
1258 
            expect_neg_dqs = 0;
1259 
        end
1260 
    end
1261 
    endtask
1262 
 
1263 
    task check_pos_dqs;
1264 
    begin
1265 
        if (Write_cmnd[2] || Write_cmnd[1] || Data_in_enable) begin
1266 
            for (i=0; i<DQS_BITS; i=i+1) begin
1267 
                if (expect_pos_dqs[i]) begin
1268 
                    $display ("At time %t ERROR: Positive DQS[%1d] transition required.", $time, i);
1269 
                end
1270 
                expect_pos_dqs[i] = 1'b1;
1271 
            end
1272 
        end else begin
1273 
            expect_pos_dqs = 0;
1274 
            expect_neg_dqs = 0;
1275 
        end
1276 
    end
1277 
    endtask
1278 
 
1279 
    // Main Logic
1280 
    always @ (posedge Sys_clk) begin
1281 
        Manual_Precharge_Pipeline;
1282 
        Burst_Terminate_Pipeline;
1283 
        Dq_Dqs_Drivers;
1284 
        Write_FIFO_DM_Mask_Logic;
1285 
        Burst_Decode;
1286 
        check_neg_dqs;
1287 
        Auto_Precharge_Calculation;
1288 
        DLL_Counter;
1289 
        Control_Logic;
1290 
    end
1291 
 
1292 
    always @ (negedge Sys_clk) begin
1293 
        Manual_Precharge_Pipeline;
1294 
        Burst_Terminate_Pipeline;
1295 
        Dq_Dqs_Drivers;
1296 
        Write_FIFO_DM_Mask_Logic;
1297 
        Burst_Decode;
1298 
        check_pos_dqs;
1299 
    end
1300 
 
1301 
    // Dqs Receiver
1302 
    always @ (posedge Dqs_in[0]) begin
1303 
        // Latch data at posedge Dqs
1304 
        dq_rise[7 : 0] = Dq_in[7 : 0];
1305 
        dm_rise[0] = Dm_in[0];
1306 
        expect_pos_dqs[0] = 0;
1307 
    end
1308 
 
1309 
    always @ (posedge Dqs_in[1]) begin
1310 
        // Latch data at posedge Dqs
1311 
        dq_rise[15 : 8] = Dq_in[15 : 8];
1312 
        dm_rise[1] = Dm_in [1];
1313 
        expect_pos_dqs[1] = 0;
1314 
    end
1315 
 
1316 
    always @ (negedge Dqs_in[0]) begin
1317 
        // Latch data at negedge Dqs
1318 
        dq_fall[7 : 0] = Dq_in[7 : 0];
1319 
        dm_fall[0] = Dm_in[0];
1320 
        dm_pair[1:0]  = {dm_rise[0], dm_fall[0]};
1321 
        expect_neg_dqs[0] = 0;
1322 
    end
1323 
 
1324 
    always @ (negedge Dqs_in[1]) begin
1325 
        // Latch data at negedge Dqs
1326 
        dq_fall[15: 8] = Dq_in[15 : 8];
1327 
        dm_fall[1] = Dm_in[1];
1328 
        dm_pair[3:2]  = {dm_rise[1], dm_fall[1]};
1329 
        expect_neg_dqs[1] = 0;
1330 
    end
1331 
 
1332 
    specify
1333 
                                              // SYMBOL UNITS DESCRIPTION
1334 
                                              // ------ ----- -----------
1335 
//`ifdef sg5B                                   //              specparams for -5B (CL = 3)
1336 
//        specparam tDSS             =     1.0; // tDSS   ns    DQS falling edge to CLK rising (setup time) = 0.2*tCK
1337 
//        specparam tDSH             =     1.0; // tDSH   ns    DQS falling edge from CLK rising (hold time) = 0.2*tCK
1338 
//        specparam tIH              =   0.600; // tIH    ns    Input Hold Time
1339 
//        specparam tIS              =   0.600; // tIS    ns    Input Setup Time
1340 
//        specparam tDQSH            =    1.75; // tDQSH  ns    DQS input High Pulse Width = 0.35*tCK
1341 
//        specparam tDQSL            =    1.75; // tDQSL  ns    DQS input Low Pulse Width = 0.35*tCK
1342 
//`else `ifdef sg6                              //              specparams for -6 (CL = 2.5)
1343 
        specparam tDSS             =     1.2; // tDSS   ns    DQS falling edge to CLK rising (setup time) = 0.2*tCK
1344 
        specparam tDSH             =     1.2; // tDSH   ns    DQS falling edge from CLK rising (hold time) = 0.2*tCK
1345 
        specparam tIH              =   0.750; // tIH    ns    Input Hold Time
1346 
        specparam tIS              =   0.750; // tIS    ns    Input Setup Time
1347 
        specparam tDQSH            =     2.1; // tDQSH  ns    DQS input High Pulse Width = 0.35*tCK
1348 
        specparam tDQSL            =     2.1; // tDQSL  ns    DQS input Low Pulse Width = 0.35*tCK
1349 
//`else `ifdef sg75E                            //              specparams for -75E (CL = 2)
1350 
//        specparam tDSS             =     1.5; // tDSS   ns    DQS falling edge to CLK rising (setup time) = 0.2*tCK
1351 
//        specparam tDSH             =     1.5; // tDSH   ns    DQS falling edge from CLK rising (hold time) = 0.2*tCK
1352 
//        specparam tIH              =   0.900; // tIH    ns    Input Hold Time
1353 
//        specparam tIS              =   0.900; // tIS    ns    Input Setup Time
1354 
//        specparam tDQSH            =   2.625; // tDQSH  ns    DQS input High Pulse Width = 0.35*tCK
1355 
//        specparam tDQSL            =   2.625; // tDQSL  ns    DQS input Low Pulse Width = 0.35*tCK
1356 
//`else
1357 
//`define sg75Z                           //              specparams for -75Z (CL = 2)
1358 
//        specparam tDSS             =     1.5; // tDSS   ns    DQS falling edge to CLK rising (setup time) = 0.2*tCK
1359 
//        specparam tDSH             =     1.5; // tDSH   ns    DQS falling edge from CLK rising (hold time) = 0.2*tCK
1360 
//        specparam tIH              =   0.900; // tIH    ns    Input Hold Time
1361 
//        specparam tIS              =   0.900; // tIS    ns    Input Setup Time
1362 
//        specparam tDQSH            =   2.625; // tDQSH  ns    DQS input High Pulse Width = 0.35*tCK
1363 
//        specparam tDQSL            =   2.625; // tDQSL  ns    DQS input Low Pulse Width = 0.35*tCK
1364 
//`endif `endif `endif
1365 
        $width    (posedge Dqs_in[0] &&& wdqs_valid, tDQSH);
1366 
        $width    (posedge Dqs_in[1] &&& wdqs_valid, tDQSH);
1367 
        $width    (negedge Dqs_in[0] &&& wdqs_valid, tDQSL);
1368 
        $width    (negedge Dqs_in[1] &&& wdqs_valid, tDQSL);
1369 
        $setuphold(posedge Clk,   Cke,   tIS, tIH);
1370 
        $setuphold(posedge Clk,   Cs_n,  tIS, tIH);
1371 
        $setuphold(posedge Clk,   Cas_n, tIS, tIH);
1372 
        $setuphold(posedge Clk,   Ras_n, tIS, tIH);
1373 
        $setuphold(posedge Clk,   We_n,  tIS, tIH);
1374 
        $setuphold(posedge Clk,   Addr,  tIS, tIH);
1375 
        $setuphold(posedge Clk,   Ba,    tIS, tIH);
1376 
        $setuphold(posedge Clk, negedge Dqs &&& wdqs_valid, tDSS, tDSH);
1377 
    endspecify
1378 
 
1379 
endmodule

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