src/cpu/minor/decode.hh

   1 /*
   2  * Copyright (c) 2013-2014 ARM Limited
   3  * All rights reserved
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   9  * licensed hereunder.  You may use the software subject to the license
  10  * terms below provided that you ensure that this notice is replicated
  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Redistribution and use in source and binary forms, with or without
  15  * modification, are permitted provided that the following conditions are
  16  * met: redistributions of source code must retain the above copyright
  17  * notice, this list of conditions and the following disclaimer;
  18  * redistributions in binary form must reproduce the above copyright
  19  * notice, this list of conditions and the following disclaimer in the
  20  * documentation and/or other materials provided with the distribution;
  21  * neither the name of the copyright holders nor the names of its
  22  * contributors may be used to endorse or promote products derived from
  23  * this software without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  26  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  27  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  28  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  29  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  30  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  31  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  32  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  33  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  35  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  *
  37  * Authors: Andrew Bardsley
  38  */
  39
  40 /**
  41  * @file
  42  *
  43  *  Decode collects macro-ops from Fetch2 and splits them into micro-ops
  44  *  passed to Execute.
  45  */
  46
  47 #ifndef __CPU_MINOR_DECODE_HH__
  48 #define __CPU_MINOR_DECODE_HH__
  49
  50 #include "cpu/minor/buffers.hh"
  51 #include "cpu/minor/cpu.hh"
  52 #include "cpu/minor/dyn_inst.hh"
  53 #include "cpu/minor/pipe_data.hh"
  54
  55 namespace Minor
  56 {
  57
  58 /* Decode takes instructions from Fetch2 and decomposes them into micro-ops
  59  * to feed to Execute.  It generates a new sequence number for each
  60  * instruction: execSeqNum.
  61  */
  62 class Decode : public Named
  63 {
  64   protected:
  65     /** Pointer back to the containing CPU */
  66     MinorCPU &cpu;
  67
  68     /** Input port carrying macro instructions from Fetch2 */
  69     Latch<ForwardInstData>::Output inp;
  70     /** Output port carrying micro-op decomposed instructions to Execute */
  71     Latch<ForwardInstData>::Input out;
  72
  73     /** Interface to reserve space in the next stage */
  74     std::vector<InputBuffer<ForwardInstData>> &nextStageReserve;
  75
  76     /** Width of output of this stage/input of next in instructions */
  77     unsigned int outputWidth;
  78
  79     /** If true, more than one input word can be processed each cycle if
  80      *  there is room in the output to contain its processed data */
  81     bool processMoreThanOneInput;
  82
  83   public:
  84     /* Public for Pipeline to be able to pass it to Fetch2 */
  85     std::vector<InputBuffer<ForwardInstData>> inputBuffer;
  86
  87   protected:
  88     /** Data members after this line are cycle-to-cycle state */
  89
  90     struct DecodeThreadInfo {
  91
  92         /** Default Constructor */
  93         DecodeThreadInfo() :
  94             inputIndex(0),
  95             inMacroop(false),
  96             execSeqNum(InstId::firstExecSeqNum),
  97             blocked(false)
  98         { }
  99
 100         DecodeThreadInfo(const DecodeThreadInfo& other) :
 101             inputIndex(other.inputIndex),
 102             inMacroop(other.inMacroop),
 103             execSeqNum(other.execSeqNum),
 104             blocked(other.blocked)
 105         { }
 106
 107
 108         /** Index into the inputBuffer's head marking the start of unhandled
 109          *  instructions */
 110         unsigned int inputIndex;
 111
 112         /** True when we're in the process of decomposing a micro-op and
 113          *  microopPC will be valid.  This is only the case when there isn't
 114          *  sufficient space in Executes input buffer to take the whole of a
 115          *  decomposed instruction and some of that instructions micro-ops must
 116          *  be generated in a later cycle */
 117         bool inMacroop;
 118         TheISA::PCState microopPC;
 119
 120         /** Source of execSeqNums to number instructions. */
 121         InstSeqNum execSeqNum;
 122
 123         /** Blocked indication for report */
 124         bool blocked;
 125     };
 126
 127     std::vector<DecodeThreadInfo> decodeInfo;
 128     ThreadID threadPriority;
 129
 130   protected:
 131     /** Get a piece of data to work on, or 0 if there is no data. */
 132     const ForwardInstData *getInput(ThreadID tid);
 133
 134     /** Pop an element off the input buffer, if there are any */
 135     void popInput(ThreadID tid);
 136
 137     /** Use the current threading policy to determine the next thread to
 138      *  decode from. */
 139     ThreadID getScheduledThread();
 140   public:
 141     Decode(const std::string &name,
 142         MinorCPU &cpu_,
 143         MinorCPUParams &params,
 144         Latch<ForwardInstData>::Output inp_,
 145         Latch<ForwardInstData>::Input out_,
 146         std::vector<InputBuffer<ForwardInstData>> &next_stage_input_buffer);
 147
 148   public:
 149     /** Pass on input/buffer data to the output if you can */
 150     void evaluate();
 151
 152     void minorTrace() const;
 153
 154     /** Is this stage drained?  For Decoed, draining is initiated by
 155      *  Execute halting Fetch1 causing Fetch2 to naturally drain
 156      *  into Decode and on to Execute which is responsible for
 157      *  actually killing instructions */
 158     bool isDrained();
 159 };
 160
 161 }
 162
 163 #endif /* __CPU_MINOR_DECODE_HH__ */