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/* branch_predict.c -- branch prediction simulation

   Copyright (C) 1999 Damjan Lampret, lampret@opencores.org

This file is part of OpenRISC 1000 Architectural Simulator.

This program is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2 of the License, or

(at your option) any later version.

This program is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

GNU General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */

/* Branch prediction functions.

   At the moment this functions only simulate functionality of branch

   prediction and do not influence on fetche/decode/execute stages.

   They are here only to verify performance of various branch

   prediction configurations.

 */

#include <stdio.h>

#include <string.h>

#include <errno.h>

#include <stdarg.h>

#include "branch_predict.h"

#include "abstract.h"

#include "stats.h"

/* Branch prediction buffer */

/* Length of BPB */

#define BPB_LEN 64

/* Number of BPB ways (1, 2, 3 etc.). */

#define BPB_WAYS 1

/* Number of prediction states (2, 4, 8 etc.). */

#define BPB_PSTATES 2

/* Number of usage states (2, 3, 4 etc.). */

#define BPB_USTATES 2

/* branch prediction buffer entry */

struct bpb_entry {

        struct {

                unsigned long addr;     /* address of a branch insn */

                int taken;              /* taken == 1, not taken == 0  OR */

                                        /* strongly taken == 3, taken == 2,

                                           not taken == 1, strongly not taken == 0 */

                int lru;                /* least recently == 0 */

        } way[BPB_WAYS];

} bpb[BPB_LEN];

void bpb_info()

{

        printf("BPB %d bytes: ", BPB_LEN * BPB_WAYS * (BPB_PSTATES + BPB_USTATES) / 8);

        printf("%d ways, %d sets, %d bits/prediction\n", BPB_WAYS, BPB_LEN, BPB_PSTATES + BPB_USTATES);

}

/* First check if branch is already in the cache and if it is:

    - increment BPB hit stats,

    - set 'lru' at this way to BPB_USTATES - 1 and

      decrement 'lru' of other ways unless they have reached 0,

    - increment correct/incorrect stats according to BPB 'taken' field

      and 'taken' variable,

    - increment or decrement BPB taken field according to 'taken' variable

   and if not:

    - increment BPB miss stats

    - find lru way and entry and replace old address with 'addr' and

      'taken' field with (BPB_PSTATES/2 - 1) + 'taken'

    - set 'lru' with BPB_USTATES - 1 and decrement 'lru' of other

      ways unless they have reached 0

*/

void bpb_update(unsigned long addr, int taken)

{

        int entry, way = -1;

        int i;

        /* Calc entry. */

        entry = addr % BPB_LEN;

        /* Scan all ways and try to find our addr. */

        for (i = 0; i < BPB_WAYS; i++)

                if (bpb[entry].way[i].addr == addr)

                        way = i;

        /* Did we find our cached branch? */

        if (way >= 0) { /* Yes, we did. */

                mstats.bpb.hit++;

                for (i = 0; i < BPB_WAYS; i++)

                        if (bpb[entry].way[i].lru)

                                bpb[entry].way[i].lru--;

                bpb[entry].way[way].lru = BPB_USTATES - 1;

                if (bpb[entry].way[way].taken / (BPB_PSTATES / 2) == taken)

                        mstats.bpb.correct++;

                else

                        mstats.bpb.incorrect++;

                if (taken && (bpb[entry].way[way].taken < BPB_PSTATES - 1))

                        bpb[entry].way[way].taken++;

                else

                if (!taken && (bpb[entry].way[way].taken))

                        bpb[entry].way[way].taken--;

        }

        else {  /* No, we didn't. */

                int minlru = BPB_USTATES - 1;

                int minway = 0;

                mstats.bpb.miss++;

                for (i = 0; i < BPB_WAYS; i++)

                        if (bpb[entry].way[i].lru < minlru)

                                minway = i;

                bpb[entry].way[minway].addr = addr;

                bpb[entry].way[minway].taken = (BPB_PSTATES / 2 - 1) + taken;

                for (i = 0; i < BPB_WAYS; i++)

                        if (bpb[entry].way[i].lru)

                                bpb[entry].way[i].lru--;

                bpb[entry].way[minway].lru = BPB_USTATES - 1;

        }

}

/* Branch target instruction cache */

/* Length of BTIC */

#define BTIC_LEN 128

/* Number of BTIC ways (1, 2, 3 etc.). */

#define BTIC_WAYS 2

/* Number of usage states (2, 3, 4 etc.). */

#define BTIC_USTATES 2

/* Target block size in bytes. */

#define BTIC_BLOCKSIZE 4

struct btic_entry {

        struct {

                unsigned long addr;     /* cached target address of a branch */

                int lru;                /* least recently used */

                char *insn;             /* cached insn at target address (not used currently) */

        } way[BTIC_WAYS];

} btic[BTIC_LEN];

void btic_info()

{

        printf("BTIC %d bytes: ", BTIC_LEN * BTIC_WAYS * (BTIC_USTATES + BTIC_BLOCKSIZE * 8) / 8);

        printf("%d ways, %d sets, %d bits/target\n", BTIC_WAYS, BTIC_LEN, BTIC_USTATES + BTIC_BLOCKSIZE * 8);

}

/* First check if target addr is already in the cache and if it is:

    - increment BTIC hit stats,

    - set 'lru' at this way to BTIC_USTATES - 1 and

      decrement 'lru' of other ways unless they have reached 0,

   and if not:

    - increment BTIC miss stats

    - find lru way and entry and replace old address with 'addr' and

      'insn' with NULL

    - set 'lru' with BTIC_USTATES - 1 and decrement 'lru' of other

      ways unless they have reached 0

*/

void btic_update(unsigned long targetaddr)

{

        int entry, way = -1;

        int i;

        /* Calc entry. */

        entry = targetaddr % BTIC_LEN;

        /* Scan all ways and try to find our addr. */

        for (i = 0; i < BTIC_WAYS; i++)

                if (btic[entry].way[i].addr == targetaddr)

                        way = i;

        /* Did we find our cached branch? */

        if (way >= 0) { /* Yes, we did. */

                mstats.btic.hit++;

                for (i = 0; i < BTIC_WAYS; i++)

                        if (btic[entry].way[i].lru)

                                btic[entry].way[i].lru--;

                btic[entry].way[way].lru = BTIC_USTATES - 1;

        }

        else {  /* No, we didn't. */

                int minlru = BTIC_USTATES - 1;

                int minway = 0;

                mstats.btic.miss++;

                for (i = 0; i < BTIC_WAYS; i++)

                        if (btic[entry].way[i].lru < minlru)

                                minway = i;

                btic[entry].way[minway].addr = targetaddr;

                btic[entry].way[minway].insn = NULL;

                for (i = 0; i < BTIC_WAYS; i++)

                        if (btic[entry].way[i].lru)

                                btic[entry].way[i].lru--;

                btic[entry].way[minway].lru = BTIC_USTATES - 1;

        }

}