btb.cc revision 6226:f1076450ab2b
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 "base/intmath.hh" 32#include "base/trace.hh" 33#include "cpu/pred/btb.hh" 34 35DefaultBTB::DefaultBTB(unsigned _numEntries, 36 unsigned _tagBits, 37 unsigned _instShiftAmt) 38 : numEntries(_numEntries), 39 tagBits(_tagBits), 40 instShiftAmt(_instShiftAmt) 41{ 42 DPRINTF(Fetch, "BTB: Creating BTB object.\n"); 43 44 if (!isPowerOf2(numEntries)) { 45 fatal("BTB entries is not a power of 2!"); 46 } 47 48 btb.resize(numEntries); 49 50 for (int i = 0; i < numEntries; ++i) { 51 btb[i].valid = false; 52 } 53 54 idxMask = numEntries - 1; 55 56 tagMask = (1 << tagBits) - 1; 57 58 tagShiftAmt = instShiftAmt + floorLog2(numEntries); 59} 60 61void 62DefaultBTB::reset() 63{ 64 for (int i = 0; i < numEntries; ++i) { 65 btb[i].valid = false; 66 } 67} 68 69inline 70unsigned 71DefaultBTB::getIndex(const Addr &inst_PC) 72{ 73 // Need to shift PC over by the word offset. 74 return (inst_PC >> instShiftAmt) & idxMask; 75} 76 77inline 78Addr 79DefaultBTB::getTag(const Addr &inst_PC) 80{ 81 return (inst_PC >> tagShiftAmt) & tagMask; 82} 83 84bool 85DefaultBTB::valid(const Addr &inst_PC, ThreadID tid) 86{ 87 unsigned btb_idx = getIndex(inst_PC); 88 89 Addr inst_tag = getTag(inst_PC); 90 91 assert(btb_idx < numEntries); 92 93 if (btb[btb_idx].valid 94 && inst_tag == btb[btb_idx].tag 95 && btb[btb_idx].tid == tid) { 96 return true; 97 } else { 98 return false; 99 } 100} 101 102// @todo Create some sort of return struct that has both whether or not the 103// address is valid, and also the address. For now will just use addr = 0 to 104// represent invalid entry. 105Addr 106DefaultBTB::lookup(const Addr &inst_PC, ThreadID tid) 107{ 108 unsigned btb_idx = getIndex(inst_PC); 109 110 Addr inst_tag = getTag(inst_PC); 111 112 assert(btb_idx < numEntries); 113 114 if (btb[btb_idx].valid 115 && inst_tag == btb[btb_idx].tag 116 && btb[btb_idx].tid == tid) { 117 return btb[btb_idx].target; 118 } else { 119 return 0; 120 } 121} 122 123void 124DefaultBTB::update(const Addr &inst_PC, const Addr &target, ThreadID tid) 125{ 126 unsigned btb_idx = getIndex(inst_PC); 127 128 assert(btb_idx < numEntries); 129 130 btb[btb_idx].tid = tid; 131 btb[btb_idx].valid = true; 132 btb[btb_idx].target = target; 133 btb[btb_idx].tag = getTag(inst_PC); 134} 135