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;

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30
31#include "base/intmath.hh"
32#include "base/trace.hh"
33#include "cpu/pred/btb.hh"
34#include "debug/Fetch.hh"
35
36DefaultBTB::DefaultBTB(unsigned _numEntries,
37 unsigned _tagBits,
38 unsigned _instShiftAmt)
39 : numEntries(_numEntries),
40 tagBits(_tagBits),
41 instShiftAmt(_instShiftAmt)
42{
43 DPRINTF(Fetch, "BTB: Creating BTB object.\n");
44
45 if (!isPowerOf2(numEntries)) {
46 fatal("BTB entries is not a power of 2!");
47 }
48
49 btb.resize(numEntries);

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64{
65 for (unsigned i = 0; i < numEntries; ++i) {
66 btb[i].valid = false;
67 }
68}
69
70inline
71unsigned
72DefaultBTB::getIndex(Addr instPC)
73{
74 // Need to shift PC over by the word offset.
75 return (instPC >> instShiftAmt) & idxMask;
76}
77
78inline
79Addr
80DefaultBTB::getTag(Addr instPC)
81{
82 return (instPC >> tagShiftAmt) & tagMask;
83}
84
85bool
86DefaultBTB::valid(Addr instPC, ThreadID tid)
87{
88 unsigned btb_idx = getIndex(instPC);
89
90 Addr inst_tag = getTag(instPC);
91
92 assert(btb_idx < numEntries);
93
94 if (btb[btb_idx].valid
95 && inst_tag == btb[btb_idx].tag
96 && btb[btb_idx].tid == tid) {

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101}
102
103// @todo Create some sort of return struct that has both whether or not the
104// address is valid, and also the address. For now will just use addr = 0 to
105// represent invalid entry.
106TheISA::PCState
107DefaultBTB::lookup(Addr instPC, ThreadID tid)
108{
109 unsigned btb_idx = getIndex(instPC);
110
111 Addr inst_tag = getTag(instPC);
112
113 assert(btb_idx < numEntries);
114
115 if (btb[btb_idx].valid
116 && inst_tag == btb[btb_idx].tag
117 && btb[btb_idx].tid == tid) {
118 return btb[btb_idx].target;
119 } else {
120 return 0;
121 }
122}
123
124void
125DefaultBTB::update(Addr instPC, const TheISA::PCState &target, ThreadID tid)
126{
127 unsigned btb_idx = getIndex(instPC);
128
129 assert(btb_idx < numEntries);
130
131 btb[btb_idx].tid = tid;
132 btb[btb_idx].valid = true;
133 btb[btb_idx].target = target;
134 btb[btb_idx].tag = getTag(instPC);
135}