3_02ifu

大型risc处理器设计源代码,这是书中的代码 基于流水线的risc cpu设计

  wire          ID_ANNUL,           // present ANNUL bit                         a0447
                BRANCH,             // branch                                    a0448
                TYPE,               // BCC or CALL, if branch                    a0449
                DS_NOW,             // CTR in ID, delay slot in IF               a0450
                TAKEN,              // present branch was taken                  a0451
                KU_MODE,            // kernel/user mode                          a0452
                LAST_KU_MODE,       // last kernel/user mode                     a0453
                IGNORE_HIT,         // ignore cache hit                          a0454
                CCLR,               // clear cache                               a0455
                NEW_FLAGS,          // instruction in ID changes flags           a0456
                NO_ACC,             // no memory access possible                 a0457
                WORK_IF,            // IF is active                              a0458
                DO_IF,              // IF was activated                          a0459
                nRESET,             // reset                                     a0460
                CP;                 // system clock                              a0461
                                                                                 a0462
  // Internal wiring                                                             a0463
  wire [31:0]   DELAYSLOT;          // delay slot from cache                     a0464
  wire [29:0]   TARGET,             // branch target from cache                  a0465
                LAST_TARGET;        // last branch target from PCL               a0466
  wire [3:0]    CCODE,              // condition code from cache                 a0467
                LAST_CCODE;         // last condition code from PCL              a0468
  wire [1:0]    HIBITS,             // history bits from cache                   a0469
                LAST_HIBITS,        // last history bits from PCL                a0470
                NEW_HIBITS;         // new history bits from HUL                 a0471
  wire          WnR,                // write/read signal for cache               a0472
                UPDATE,             // update signal for cache                   a0473
                NOW_TAKEN,          // branch from cache to be taken             a0474
                LAST_TAKEN,         // final branch decision                     a0475
                HITAKEN,            // branch decision based on HIBITS           a0476
                LAST_HITAKEN,       // last heuristic branch decision            a0477
                LAST_NEW_FLAGS,     // last decision was heuristic               a0478
                LAST_HIT,           // there was a hit                           a0479
                ANNUL,              // ANNUL bit from cache                      a0480
                LAST_ANNUL;         // last ANNUL bit from PCL                   a0481
                                                                                 a0482
  // Internal registers                                                          a0483
  reg           TAKE;               // modified TAKEN from CALL write mux        a0484
                                                                                 a0485
  //                                                                             a0486
  // Instances                                                                   a0487
  //                                                                             a0488
                                                                                 a0489
  // Read-write logic                                                            a0490
  rwl     RWL       (WnR, UPDATE,                                                a0491
                     CONFIG[1:0], BRANCH, TYPE, LAST_HIT, LAST_TYPE,             a0492
                     NO_ACC, DO_IF, nRESET, CP);                                 a0493
                                                                                 a0494
  // Branch cache                                                                a0495
  bcache  BCACHE    (BTC_DELAYSLOT, TARGET, CCODE, HIBITS, BTC_HIT, ANNUL,       a0496
                     OPCODE, JPC, LPC, PC, ID_CCODE, NEW_HIBITS, DS_NOW,         a0497
                     ID_ANNUL, TAKE, KU_MODE, LAST_KU_MODE, WnR, UPDATE,         a0498
                     WORK_IF, DO_IF, CCLR, nRESET, CP);                          a0499
                                                                                 a0500
  // Call detection logic                                                        a0501
  cdl     CDL       (BTC_TYPE, CCODE, HITAKEN);                                  a0502
                                                                                 a0503
  // Branch decision logic                                                       a0504
  bdl     NOW_BDL   (NOW_TAKEN, FLAGS_IF, CCODE);                                a0505
                                                                                 a0506
  // History decision logic                                                      a0507
  hil     HIL       (HITAKEN, HIBITS);                                           a0508
                                                                                 a0509
  // Pipeline control logic                                                      a0510
  pcl     PCL       (LAST_TARGET,                                                a0511
                     LAST_HIT, LAST_ANNUL, LAST_HITAKEN, LAST_NEW_FLAGS,         a0512
                     LAST_HIBITS, LAST_CCODE, LAST_TYPE,                         a0513
                     TARGET, BTC_HIT & ~BTC_CORRECT, ANNUL, HITAKEN, NEW_FLAGS,  a0514
                     HIBITS, CCODE, BTC_TYPE, IGNORE_HIT, WORK_IF, CP);          a0515
                                                                                 a0516
  // Branch correction logic                                                     a0517
  bcl     BCL       (BTC_CORRECT, BTC_USE_LAST, BTC_DIS_ALU,                     a0518
                     LAST_HIT, LAST_ANNUL, LAST_HITAKEN, LAST_TAKEN,             a0519
                     LAST_NEW_FLAGS, LAST_TYPE);                                 a0520
                                                                                 a0521
  // Branch decision logic                                                       a0522
  bdl     LAST_BDL  (LAST_TAKEN, FLAGS_FD, LAST_CCODE);                          a0523
                                                                                 a0524
  // History update logic                                                        a0525
  hul     HUL       (NEW_HIBITS, LAST_HIBITS, LAST_TAKEN);                       a0526
                                                                                 a0527
                                                                                 a0528
  //                                                                             a0529
  // PC multiplexer                                                              a0530
  //                                                                             a0531
  // Depending on a necessary branch correction,                                 a0532
  // the branch target is selected from cache                                    a0533
  // or from last access.                                                        a0534
  //                                                                             a0535
  always @(BTC_USE_LAST or TARGET or LAST_TARGET) begin                          a0536
    casez(BTC_USE_LAST)                                                          a0537
      1'b0    : BTC_PC = TARGET;                    // branch target from cache  a0538
      1'b1    : BTC_PC = LAST_TARGET;               // last branch target        a0539
      default : BTC_PC = 30'bx;                                                  a0540
    endcase                                                                      a0541
  end                                                                            a0542
                                                                                 a0543
  //                                                                             a0544
  // Taken multiplexer                                                           a0545
  //                                                                             a0546
  // If the instruction in the ALU changes the flags,                            a0547
  // indicated by NEW_FLAGS, the branch decision has to be made                  a0548
  // heuristically using the history bits from the cache,                        a0549
  // except for a CALL. If the flags are not changed,                            a0550
  // the decision can be made using the present flags.                           a0551
  //                                                                             a0552
  always @(NEW_FLAGS or BTC_TYPE or HITAKEN or NOW_TAKEN) begin                  a0553
    casez({NEW_FLAGS, BTC_TYPE})                                                 a0554
      2'b0?   : BTC_TAKEN = NOW_TAKEN;                  // normal decision       a0555
      2'b10   : BTC_TAKEN = HITAKEN;                    // heuristic             a0556
      2'b11   : BTC_TAKEN = 1'b1;                       // unconditional (CALL)  a0557
      default : BTC_TAKEN = 1'bx;                                                a0558
    endcase                                                                      a0559
  end                                                                            a0560
                                                                                 a0561
  //                                                                             a0562
  // CALL write multiplexer                                                      a0563
  //                                                                             a0564
  // A CALL is stored in the cache as a BT, i.e.,                                a0565
  // as a conditional branch which is always taken.                              a0566
  // The PCU needs to know whether there is a                                    a0567
  // CALL so that the return address can be saved.                               a0568
  // To save one bit per line, the CALL is stored                                a0569
  // as a non-taken BT. Therefore, the signal TAKEN                              a0570
  // has to be changed for the storage of CALLs.                                 a0571
  //                                                                             a0572
  always @(TYPE or TAKEN) begin                                                  a0573
    casez(TYPE)                                                                  a0574
      1'b0 : TAKE = TAKEN;                              // BCC                   a0575
      1'b1 : TAKE = 1'b0;                               // CALL                  a0576
      default : TAKE = TAKEN;                                                    a0577
    endcase                                                                      a0578
  end                                                                            a0579
                                                                                 a0580
  //                                                                             a0581
  // DIS_IDU multiplexer                                                         a0582
  //                                                                             a0583
  // BTC_DIS_IDU depends on whether there                                        a0584
  // is a hit, a correction, or none of both.                                    a0585
  // The special case of a hit without final flags                               a0586
  // has to be observed. Then BTC_DIS_IDU is not set.                            a0587
  // Instead, the ALU is turned off in the next step.                            a0588
  // Signal DIS_ALU is generated by BCL.                                         a0589
  //                                                                             a0590
  always @(BTC_CORRECT or BTC_HIT or NEW_FLAGS                                   a0591
            or ANNUL or BTC_TAKEN) begin                                         a0592
    casez({BTC_CORRECT, BTC_HIT, NEW_FLAGS})                                     a0593
      3'b00? : BTC_DIS_IDU = 1'b0;                                               a0594
      3'b010 : BTC_DIS_IDU = ANNUL & ~BTC_TAKEN;                                 a0595