1/*
2 * Copyright (c) 2004-2005 The Regents of The University of Michigan
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Kevin Lim
29 */
30
31#include "cpu/pred/btb.hh"
32
33#include "base/intmath.hh"
34#include "base/trace.hh"
33#include "cpu/pred/btb.hh"
35#include "debug/Fetch.hh"
36
37DefaultBTB::DefaultBTB(unsigned _numEntries,
38 unsigned _tagBits,
39 unsigned _instShiftAmt,
40 unsigned _num_threads)
41 : numEntries(_numEntries),
42 tagBits(_tagBits),
43 instShiftAmt(_instShiftAmt),
44 log2NumThreads(floorLog2(_num_threads))
45{
46 DPRINTF(Fetch, "BTB: Creating BTB object.\n");
47
48 if (!isPowerOf2(numEntries)) {
49 fatal("BTB entries is not a power of 2!");
50 }
51
52 btb.resize(numEntries);
53
54 for (unsigned i = 0; i < numEntries; ++i) {
55 btb[i].valid = false;
56 }
57
58 idxMask = numEntries - 1;
59
60 tagMask = (1 << tagBits) - 1;
61
62 tagShiftAmt = instShiftAmt + floorLog2(numEntries);
63}
64
65void
66DefaultBTB::reset()
67{
68 for (unsigned i = 0; i < numEntries; ++i) {
69 btb[i].valid = false;
70 }
71}
72
73inline
74unsigned
75DefaultBTB::getIndex(Addr instPC, ThreadID tid)
76{
77 // Need to shift PC over by the word offset.
78 return ((instPC >> instShiftAmt)
79 ^ (tid << (tagShiftAmt - instShiftAmt - log2NumThreads)))
80 & idxMask;
81}
82
83inline
84Addr
85DefaultBTB::getTag(Addr instPC)
86{
87 return (instPC >> tagShiftAmt) & tagMask;
88}
89
90bool
91DefaultBTB::valid(Addr instPC, ThreadID tid)
92{
93 unsigned btb_idx = getIndex(instPC, tid);
94
95 Addr inst_tag = getTag(instPC);
96
97 assert(btb_idx < numEntries);
98
99 if (btb[btb_idx].valid
100 && inst_tag == btb[btb_idx].tag
101 && btb[btb_idx].tid == tid) {
102 return true;
103 } else {
104 return false;
105 }
106}
107
108// @todo Create some sort of return struct that has both whether or not the
109// address is valid, and also the address. For now will just use addr = 0 to
110// represent invalid entry.
111TheISA::PCState
112DefaultBTB::lookup(Addr instPC, ThreadID tid)
113{
114 unsigned btb_idx = getIndex(instPC, tid);
115
116 Addr inst_tag = getTag(instPC);
117
118 assert(btb_idx < numEntries);
119
120 if (btb[btb_idx].valid
121 && inst_tag == btb[btb_idx].tag
122 && btb[btb_idx].tid == tid) {
123 return btb[btb_idx].target;
124 } else {
125 return 0;
126 }
127}
128
129void
130DefaultBTB::update(Addr instPC, const TheISA::PCState &target, ThreadID tid)
131{
132 unsigned btb_idx = getIndex(instPC, tid);
133
134 assert(btb_idx < numEntries);
135
136 btb[btb_idx].tid = tid;
137 btb[btb_idx].valid = true;
138 btb[btb_idx].target = target;
139 btb[btb_idx].tag = getTag(instPC);
140}