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  • This comparison shows the changes necessary to convert path 
    /or1k/tags/or1k-1_0/or1ksim/bpb
    from Rev 249 to Rev 1765
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Rev 249 → Rev 1765

/branch_predict.c
0,0 → 1,199
/* 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 32
 
/* Number of BPB ways (1, 2, 3 etc.). */
#define BPB_WAYS 2
 
/* 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];
 
/* 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 32
 
/* Number of BTIC ways (1, 2, 3 etc.). */
#define BTIC_WAYS 2
 
/* Number of usage states (2, 3, 4 etc.). */
#define BTIC_USTATES 2
 
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];
 
/* 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;
}
}
/branch_predict.h
0,0 → 1,22
/* branch_predict.h -- branch prediction header file
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. */
 
/* more or less useless at the moment */
void bpb_update(unsigned long addr, int taken);

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