fetch.hh revision 1689 
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
29// Todo: SMT fetch,
30// Add a way to get a stage's current status.
31
32#ifndef __CPU_BETA_CPU_SIMPLE_FETCH_HH__
33#define __CPU_BETA_CPU_SIMPLE_FETCH_HH__
34
35#include "base/statistics.hh"
36#include "base/timebuf.hh"
37#include "cpu/pc_event.hh"
38#include "mem/mem_interface.hh"
39#include "sim/eventq.hh"
40
41/**
42 * SimpleFetch class to fetch a single instruction each cycle.  SimpleFetch
43 * will stall if there's an Icache miss, but otherwise assumes a one cycle
44 * Icache hit.
45 */
46
47template <class Impl>
48class SimpleFetch
49{
50  public:
51    /** Typedefs from Impl. */
52    typedef typename Impl::ISA ISA;
53    typedef typename Impl::CPUPol CPUPol;
54    typedef typename Impl::DynInst DynInst;
55    typedef typename Impl::DynInstPtr DynInstPtr;
56    typedef typename Impl::FullCPU FullCPU;
57    typedef typename Impl::Params Params;
58
59    typedef typename CPUPol::BPredUnit BPredUnit;
60    typedef typename CPUPol::FetchStruct FetchStruct;
61    typedef typename CPUPol::TimeStruct TimeStruct;
62
63    /** Typedefs from ISA. */
64    typedef typename ISA::MachInst MachInst;
65
66  public:
67    enum Status {
68        Running,
69        Idle,
70        Squashing,
71        Blocked,
72        IcacheMissStall,
73        IcacheMissComplete
74    };
75
76    // May eventually need statuses on a per thread basis.
77    Status _status;
78
79    bool stalled;
80
81  public:
82    class CacheCompletionEvent : public Event
83    {
84      private:
85        SimpleFetch *fetch;
86
87      public:
88        CacheCompletionEvent(SimpleFetch *_fetch);
89
90        virtual void process();
91        virtual const char *description();
92    };
93
94  public:
95    /** SimpleFetch constructor. */
96    SimpleFetch(Params &params);
97
98    void regStats();
99
100    void setCPU(FullCPU *cpu_ptr);
101
102    void setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer);
103
104    void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);
105
106    void processCacheCompletion();
107
108  private:
109    /**
110     * Looks up in the branch predictor to see if the next PC should be
111     * either next PC+=MachInst or a branch target.
112     * @params next_PC Next PC variable passed in by reference.  It is
113     * expected to be set to the current PC; it will be updated with what
114     * the next PC will be.
115     * @return Whether or not a branch was predicted as taken.
116     */
117    bool lookupAndUpdateNextPC(DynInstPtr &inst, Addr &next_PC);
118
119    /**
120     * Fetches the cache line that contains fetch_PC.  Returns any
121     * fault that happened.  Puts the data into the class variable
122     * cacheData.
123     * @params fetch_PC The PC address that is being fetched from.
124     * @return Any fault that occured.
125     */
126    Fault fetchCacheLine(Addr fetch_PC);
127
128    inline void doSquash(const Addr &new_PC);
129
130    void squashFromDecode(const Addr &new_PC, const InstSeqNum &seq_num);
131
132  public:
133    // Figure out PC vs next PC and how it should be updated
134    void squash(const Addr &new_PC);
135
136    void tick();
137
138    void fetch();
139
140    // Align an address (typically a PC) to the start of an I-cache block.
141    // We fold in the PISA 64- to 32-bit conversion here as well.
142    Addr icacheBlockAlignPC(Addr addr)
143    {
144        addr = ISA::realPCToFetchPC(addr);
145        return (addr & ~(cacheBlkMask));
146    }
147
148  private:
149    /** Pointer to the FullCPU. */
150    FullCPU *cpu;
151
152    /** Time buffer interface. */
153    TimeBuffer<TimeStruct> *timeBuffer;
154
155    /** Wire to get decode's information from backwards time buffer. */
156    typename TimeBuffer<TimeStruct>::wire fromDecode;
157
158    /** Wire to get rename's information from backwards time buffer. */
159    typename TimeBuffer<TimeStruct>::wire fromRename;
160
161    /** Wire to get iew's information from backwards time buffer. */
162    typename TimeBuffer<TimeStruct>::wire fromIEW;
163
164    /** Wire to get commit's information from backwards time buffer. */
165    typename TimeBuffer<TimeStruct>::wire fromCommit;
166
167    /** Internal fetch instruction queue. */
168    TimeBuffer<FetchStruct> *fetchQueue;
169
170    //Might be annoying how this name is different than the queue.
171    /** Wire used to write any information heading to decode. */
172    typename TimeBuffer<FetchStruct>::wire toDecode;
173
174    /** Icache interface. */
175    MemInterface *icacheInterface;
176
177    /** BPredUnit. */
178    BPredUnit branchPred;
179
180    /** Memory request used to access cache. */
181    MemReqPtr memReq;
182
183    /** Decode to fetch delay, in ticks. */
184    unsigned decodeToFetchDelay;
185
186    /** Rename to fetch delay, in ticks. */
187    unsigned renameToFetchDelay;
188
189    /** IEW to fetch delay, in ticks. */
190    unsigned iewToFetchDelay;
191
192    /** Commit to fetch delay, in ticks. */
193    unsigned commitToFetchDelay;
194
195    /** The width of fetch in instructions. */
196    unsigned fetchWidth;
197
198    /** Cache block size. */
199    int cacheBlkSize;
200
201    /** Mask to get a cache block's address. */
202    Addr cacheBlkMask;
203
204    /** The cache line being fetched. */
205    uint8_t *cacheData;
206
207    /** Size of instructions. */
208    int instSize;
209
210    /** Icache stall statistics. */
211    Counter lastIcacheStall;
212
213    Stats::Scalar<> icacheStallCycles;
214    Stats::Scalar<> fetchedInsts;
215    Stats::Scalar<> predictedBranches;
216    Stats::Scalar<> fetchCycles;
217    Stats::Scalar<> fetchSquashCycles;
218    Stats::Scalar<> fetchBlockedCycles;
219    Stats::Scalar<> fetchedCacheLines;
220
221    Stats::Distribution<> fetch_nisn_dist;
222};
223
224#endif //__CPU_BETA_CPU_SIMPLE_FETCH_HH__
225