src/cpu/o3/fetch.hh - public/gem5 - Git at Google

 /*
  * Copyright (c) 2010-2012, 2014 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
  * not be construed as granting a license to any other intellectual
  * property including but not limited to intellectual property relating
  * to a hardware implementation of the functionality of the software
  * licensed hereunder.  You may use the software subject to the license
  * terms below provided that you ensure that this notice is replicated
  * unmodified and in its entirety in all distributions of the software,
  * modified or unmodified, in source code or in binary form.
  *
  * Copyright (c) 2004-2006 The Regents of The University of Michigan
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met: redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer;
  * redistributions in binary form must reproduce the above copyright
  * notice, this list of conditions and the following disclaimer in the
  * documentation and/or other materials provided with the distribution;
  * neither the name of the copyright holders nor the names of its
  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  * Authors: Kevin Lim
  *          Korey Sewell
  */

 #ifndef __CPU_O3_FETCH_HH__
 #define __CPU_O3_FETCH_HH__

 #include "arch/decoder.hh"
 #include "arch/utility.hh"
 #include "base/statistics.hh"
 #include "config/the_isa.hh"
 #include "cpu/pc_event.hh"
 #include "cpu/pred/bpred_unit.hh"
 #include "cpu/timebuf.hh"
 #include "cpu/translation.hh"
 #include "mem/packet.hh"
 #include "mem/port.hh"
 #include "sim/eventq.hh"
 #include "sim/probe/probe.hh"

 struct DerivO3CPUParams;

 /**
  * DefaultFetch class handles both single threaded and SMT fetch. Its
  * width is specified by the parameters; each cycle it tries to fetch
  * that many instructions. It supports using a branch predictor to
  * predict direction and targets.
  * It supports the idling functionality of the CPU by indicating to
  * the CPU when it is active and inactive.
  */
 template <class Impl>
 class DefaultFetch
 {
   public:
     /** Typedefs from Impl. */
     typedef typename Impl::CPUPol CPUPol;
     typedef typename Impl::DynInst DynInst;
     typedef typename Impl::DynInstPtr DynInstPtr;
     typedef typename Impl::O3CPU O3CPU;

     /** Typedefs from the CPU policy. */
     typedef typename CPUPol::FetchStruct FetchStruct;
     typedef typename CPUPol::TimeStruct TimeStruct;

     /** Typedefs from ISA. */
     typedef TheISA::MachInst MachInst;

     class FetchTranslation : public BaseTLB::Translation
     {
       protected:
         DefaultFetch<Impl> *fetch;

       public:
         FetchTranslation(DefaultFetch<Impl> *_fetch)
             : fetch(_fetch)
         {}

         void
         markDelayed()
         {}

         void
         finish(const Fault &fault, const RequestPtr &req, ThreadContext *tc,
                BaseTLB::Mode mode)
         {
             assert(mode == BaseTLB::Execute);
             fetch->finishTranslation(fault, req);
             delete this;
         }
     };

   private:
     /* Event to delay delivery of a fetch translation result in case of
      * a fault and the nop to carry the fault cannot be generated
      * immediately */
     class FinishTranslationEvent : public Event
     {
       private:
         DefaultFetch<Impl> *fetch;
         Fault fault;
         RequestPtr req;

       public:
         FinishTranslationEvent(DefaultFetch<Impl> *_fetch)
             : fetch(_fetch), req(nullptr)
         {}

         void setFault(Fault _fault)
         {
             fault = _fault;
         }

         void setReq(const RequestPtr &_req)
         {
             req = _req;
         }

         /** Process the delayed finish translation */
         void process()
         {
             assert(fetch->numInst < fetch->fetchWidth);
             fetch->finishTranslation(fault, req);
         }

         const char *description() const
         {
             return "FullO3CPU FetchFinishTranslation";
         }
       };

   public:
     /** Overall fetch status. Used to determine if the CPU can
      * deschedule itsef due to a lack of activity.
      */
     enum FetchStatus {
         Active,
         Inactive
     };

     /** Individual thread status. */
     enum ThreadStatus {
         Running,
         Idle,
         Squashing,
         Blocked,
         Fetching,
         TrapPending,
         QuiescePending,
         ItlbWait,
         IcacheWaitResponse,
         IcacheWaitRetry,
         IcacheAccessComplete,
         NoGoodAddr
     };

     /** Fetching Policy, Add new policies here.*/
     enum FetchPriority {
         SingleThread,
         RoundRobin,
         Branch,
         IQ,
         LSQ
     };

   private:
     /** Fetch status. */
     FetchStatus _status;

     /** Per-thread status. */
     ThreadStatus fetchStatus[Impl::MaxThreads];

     /** Fetch policy. */
     FetchPriority fetchPolicy;

     /** List that has the threads organized by priority. */
     std::list<ThreadID> priorityList;

     /** Probe points. */
     ProbePointArg<DynInstPtr> *ppFetch;
     /** To probe when a fetch request is successfully sent. */
     ProbePointArg<RequestPtr> *ppFetchRequestSent;

   public:
     /** DefaultFetch constructor. */
     DefaultFetch(O3CPU *_cpu, DerivO3CPUParams *params);

     /** Returns the name of fetch. */
     std::string name() const;

     /** Registers statistics. */
     void regStats();

     /** Registers probes. */
     void regProbePoints();

     /** Sets the main backwards communication time buffer pointer. */
     void setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer);

     /** Sets pointer to list of active threads. */
     void setActiveThreads(std::list<ThreadID> *at_ptr);

     /** Sets pointer to time buffer used to communicate to the next stage. */
     void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);

     /** Initialize stage. */
     void startupStage();

     /** Handles retrying the fetch access. */
     void recvReqRetry();

     /** Processes cache completion event. */
     void processCacheCompletion(PacketPtr pkt);

     /** Resume after a drain. */
     void drainResume();

     /** Perform sanity checks after a drain. */
     void drainSanityCheck() const;

     /** Has the stage drained? */
     bool isDrained() const;

     /** Takes over from another CPU's thread. */
     void takeOverFrom();

     /**
      * Stall the fetch stage after reaching a safe drain point.
      *
      * The CPU uses this method to stop fetching instructions from a
      * thread that has been drained. The drain stall is different from
      * all other stalls in that it is signaled instantly from the
      * commit stage (without the normal communication delay) when it
      * has reached a safe point to drain from.
      */
     void drainStall(ThreadID tid);

     /** Tells fetch to wake up from a quiesce instruction. */
     void wakeFromQuiesce();

     /** For priority-based fetch policies, need to keep update priorityList */
     void deactivateThread(ThreadID tid);
   private:
     /** Reset this pipeline stage */
     void resetStage();

     /** Changes the status of this stage to active, and indicates this
      * to the CPU.
      */
     inline void switchToActive();

     /** Changes the status of this stage to inactive, and indicates
      * this to the CPU.
      */
     inline void switchToInactive();

     /**
      * Looks up in the branch predictor to see if the next PC should be
      * either next PC+=MachInst or a branch target.
      * @param next_PC Next PC variable passed in by reference.  It is
      * expected to be set to the current PC; it will be updated with what
      * the next PC will be.
      * @param next_NPC Used for ISAs which use delay slots.
      * @return Whether or not a branch was predicted as taken.
      */
     bool lookupAndUpdateNextPC(const DynInstPtr &inst, TheISA::PCState &pc);

     /**
      * Fetches the cache line that contains the fetch PC.  Returns any
      * fault that happened.  Puts the data into the class variable
      * fetchBuffer, which may not hold the entire fetched cache line.
      * @param vaddr The memory address that is being fetched from.
      * @param ret_fault The fault reference that will be set to the result of
      * the icache access.
      * @param tid Thread id.
      * @param pc The actual PC of the current instruction.
      * @return Any fault that occured.
      */
     bool fetchCacheLine(Addr vaddr, ThreadID tid, Addr pc);
     void finishTranslation(const Fault &fault, const RequestPtr &mem_req);


     /** Check if an interrupt is pending and that we need to handle
      */
     bool
     checkInterrupt(Addr pc)
     {
         return (interruptPending && (THE_ISA != ALPHA_ISA || !(pc & 0x3)));
     }

     /** Squashes a specific thread and resets the PC. */
     inline void doSquash(const TheISA::PCState &newPC,
                          const DynInstPtr squashInst, ThreadID tid);

     /** Squashes a specific thread and resets the PC. Also tells the CPU to
      * remove any instructions between fetch and decode that should be sqaushed.
      */
     void squashFromDecode(const TheISA::PCState &newPC,
                           const DynInstPtr squashInst,
                           const InstSeqNum seq_num, ThreadID tid);

     /** Checks if a thread is stalled. */
     bool checkStall(ThreadID tid) const;

     /** Updates overall fetch stage status; to be called at the end of each
      * cycle. */
     FetchStatus updateFetchStatus();

   public:
     /** Squashes a specific thread and resets the PC. Also tells the CPU to
      * remove any instructions that are not in the ROB. The source of this
      * squash should be the commit stage.
      */
     void squash(const TheISA::PCState &newPC, const InstSeqNum seq_num,
                 DynInstPtr squashInst, ThreadID tid);

     /** Ticks the fetch stage, processing all inputs signals and fetching
      * as many instructions as possible.
      */
     void tick();

     /** Checks all input signals and updates the status as necessary.
      *  @return: Returns if the status has changed due to input signals.
      */
     bool checkSignalsAndUpdate(ThreadID tid);

     /** Does the actual fetching of instructions and passing them on to the
      * next stage.
      * @param status_change fetch() sets this variable if there was a status
      * change (ie switching to IcacheMissStall).
      */
     void fetch(bool &status_change);

     /** Align a PC to the start of a fetch buffer block. */
     Addr fetchBufferAlignPC(Addr addr)
     {
         return (addr & ~(fetchBufferMask));
     }

     /** The decoder. */
     TheISA::Decoder *decoder[Impl::MaxThreads];

   private:
     DynInstPtr buildInst(ThreadID tid, StaticInstPtr staticInst,
                          StaticInstPtr curMacroop, TheISA::PCState thisPC,
                          TheISA::PCState nextPC, bool trace);

     /** Returns the appropriate thread to fetch, given the fetch policy. */
     ThreadID getFetchingThread(FetchPriority &fetch_priority);

     /** Returns the appropriate thread to fetch using a round robin policy. */
     ThreadID roundRobin();

     /** Returns the appropriate thread to fetch using the IQ count policy. */
     ThreadID iqCount();

     /** Returns the appropriate thread to fetch using the LSQ count policy. */
     ThreadID lsqCount();

     /** Returns the appropriate thread to fetch using the branch count
      * policy. */
     ThreadID branchCount();

     /** Pipeline the next I-cache access to the current one. */
     void pipelineIcacheAccesses(ThreadID tid);

     /** Profile the reasons of fetch stall. */
     void profileStall(ThreadID tid);

   private:
     /** Pointer to the O3CPU. */
     O3CPU *cpu;

     /** Time buffer interface. */
     TimeBuffer<TimeStruct> *timeBuffer;

     /** Wire to get decode's information from backwards time buffer. */
     typename TimeBuffer<TimeStruct>::wire fromDecode;

     /** Wire to get rename's information from backwards time buffer. */
     typename TimeBuffer<TimeStruct>::wire fromRename;

     /** Wire to get iew's information from backwards time buffer. */
     typename TimeBuffer<TimeStruct>::wire fromIEW;

     /** Wire to get commit's information from backwards time buffer. */
     typename TimeBuffer<TimeStruct>::wire fromCommit;

     //Might be annoying how this name is different than the queue.
     /** Wire used to write any information heading to decode. */
     typename TimeBuffer<FetchStruct>::wire toDecode;

     /** BPredUnit. */
     BPredUnit *branchPred;

     TheISA::PCState pc[Impl::MaxThreads];

     Addr fetchOffset[Impl::MaxThreads];

     StaticInstPtr macroop[Impl::MaxThreads];

     /** Can the fetch stage redirect from an interrupt on this instruction? */
     bool delayedCommit[Impl::MaxThreads];

     /** Memory request used to access cache. */
     RequestPtr memReq[Impl::MaxThreads];

     /** Variable that tracks if fetch has written to the time buffer this
      * cycle. Used to tell CPU if there is activity this cycle.
      */
     bool wroteToTimeBuffer;

     /** Tracks how many instructions has been fetched this cycle. */
     int numInst;

     /** Source of possible stalls. */
     struct Stalls {
         bool decode;
         bool drain;
     };

     /** Tracks which stages are telling fetch to stall. */
     Stalls stalls[Impl::MaxThreads];

     /** Decode to fetch delay. */
     Cycles decodeToFetchDelay;

     /** Rename to fetch delay. */
     Cycles renameToFetchDelay;

     /** IEW to fetch delay. */
     Cycles iewToFetchDelay;

     /** Commit to fetch delay. */
     Cycles commitToFetchDelay;

     /** The width of fetch in instructions. */
     unsigned fetchWidth;

     /** The width of decode in instructions. */
     unsigned decodeWidth;

     /** Is the cache blocked?  If so no threads can access it. */
     bool cacheBlocked;

     /** The packet that is waiting to be retried. */
     PacketPtr retryPkt;

     /** The thread that is waiting on the cache to tell fetch to retry. */
     ThreadID retryTid;

     /** Cache block size. */
     unsigned int cacheBlkSize;

     /** The size of the fetch buffer in bytes. The fetch buffer
      *  itself may be smaller than a cache line.
      */
     unsigned fetchBufferSize;

     /** Mask to align a fetch address to a fetch buffer boundary. */
     Addr fetchBufferMask;

     /** The fetch data that is being fetched and buffered. */
     uint8_t *fetchBuffer[Impl::MaxThreads];

     /** The PC of the first instruction loaded into the fetch buffer. */
     Addr fetchBufferPC[Impl::MaxThreads];

     /** The size of the fetch queue in micro-ops */
     unsigned fetchQueueSize;

     /** Queue of fetched instructions. Per-thread to prevent HoL blocking. */
     std::deque<DynInstPtr> fetchQueue[Impl::MaxThreads];

     /** Whether or not the fetch buffer data is valid. */
     bool fetchBufferValid[Impl::MaxThreads];

     /** Size of instructions. */
     int instSize;

     /** Icache stall statistics. */
     Counter lastIcacheStall[Impl::MaxThreads];

     /** List of Active Threads */
     std::list<ThreadID> *activeThreads;

     /** Number of threads. */
     ThreadID numThreads;

     /** Number of threads that are actively fetching. */
     ThreadID numFetchingThreads;

     /** Thread ID being fetched. */
     ThreadID threadFetched;

     /** Checks if there is an interrupt pending.  If there is, fetch
      * must stop once it is not fetching PAL instructions.
      */
     bool interruptPending;

     /** Set to true if a pipelined I-cache request should be issued. */
     bool issuePipelinedIfetch[Impl::MaxThreads];

     /** Event used to delay fault generation of translation faults */
     FinishTranslationEvent finishTranslationEvent;

     // @todo: Consider making these vectors and tracking on a per thread basis.
     /** Stat for total number of cycles stalled due to an icache miss. */
     Stats::Scalar icacheStallCycles;
     /** Stat for total number of fetched instructions. */
     Stats::Scalar fetchedInsts;
     /** Total number of fetched branches. */
     Stats::Scalar fetchedBranches;
     /** Stat for total number of predicted branches. */
     Stats::Scalar predictedBranches;
     /** Stat for total number of cycles spent fetching. */
     Stats::Scalar fetchCycles;
     /** Stat for total number of cycles spent squashing. */
     Stats::Scalar fetchSquashCycles;
     /** Stat for total number of cycles spent waiting for translation */
     Stats::Scalar fetchTlbCycles;
     /** Stat for total number of cycles spent blocked due to other stages in
      * the pipeline.
      */
     Stats::Scalar fetchIdleCycles;
     /** Total number of cycles spent blocked. */
     Stats::Scalar fetchBlockedCycles;
     /** Total number of cycles spent in any other state. */
     Stats::Scalar fetchMiscStallCycles;
     /** Total number of cycles spent in waiting for drains. */
     Stats::Scalar fetchPendingDrainCycles;
     /** Total number of stall cycles caused by no active threads to run. */
     Stats::Scalar fetchNoActiveThreadStallCycles;
     /** Total number of stall cycles caused by pending traps. */
     Stats::Scalar fetchPendingTrapStallCycles;
     /** Total number of stall cycles caused by pending quiesce instructions. */
     Stats::Scalar fetchPendingQuiesceStallCycles;
     /** Total number of stall cycles caused by I-cache wait retrys. */
     Stats::Scalar fetchIcacheWaitRetryStallCycles;
     /** Stat for total number of fetched cache lines. */
     Stats::Scalar fetchedCacheLines;
     /** Total number of outstanding icache accesses that were dropped
      * due to a squash.
      */
     Stats::Scalar fetchIcacheSquashes;
     /** Total number of outstanding tlb accesses that were dropped
      * due to a squash.
      */
     Stats::Scalar fetchTlbSquashes;
     /** Distribution of number of instructions fetched each cycle. */
     Stats::Distribution fetchNisnDist;
     /** Rate of how often fetch was idle. */
     Stats::Formula idleRate;
     /** Number of branch fetches per cycle. */
     Stats::Formula branchRate;
     /** Number of instruction fetched per cycle. */
     Stats::Formula fetchRate;
 };

 #endif //__CPU_O3_FETCH_HH__
	/*
	* Copyright (c) 2010-2012, 2014 ARM Limited
	* All rights reserved
	*
	* The license below extends only to copyright in the software and shall
	* not be construed as granting a license to any other intellectual
	* property including but not limited to intellectual property relating
	* to a hardware implementation of the functionality of the software
	* licensed hereunder. You may use the software subject to the license
	* terms below provided that you ensure that this notice is replicated
	* unmodified and in its entirety in all distributions of the software,
	* modified or unmodified, in source code or in binary form.
	*
	* Copyright (c) 2004-2006 The Regents of The University of Michigan
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions are
	* met: redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer;
	* redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution;
	* neither the name of the copyright holders nor the names of its
	* contributors may be used to endorse or promote products derived from
	* this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*
	* Authors: Kevin Lim
	* Korey Sewell
	*/

	#ifndef __CPU_O3_FETCH_HH__
	#define __CPU_O3_FETCH_HH__

	#include "arch/decoder.hh"
	#include "arch/utility.hh"
	#include "base/statistics.hh"
	#include "config/the_isa.hh"
	#include "cpu/pc_event.hh"
	#include "cpu/pred/bpred_unit.hh"
	#include "cpu/timebuf.hh"
	#include "cpu/translation.hh"
	#include "mem/packet.hh"
	#include "mem/port.hh"
	#include "sim/eventq.hh"
	#include "sim/probe/probe.hh"

	struct DerivO3CPUParams;

	/**
	* DefaultFetch class handles both single threaded and SMT fetch. Its
	* width is specified by the parameters; each cycle it tries to fetch
	* that many instructions. It supports using a branch predictor to
	* predict direction and targets.
	* It supports the idling functionality of the CPU by indicating to
	* the CPU when it is active and inactive.
	*/
	template <class Impl>
	class DefaultFetch
	{
	public:
	/** Typedefs from Impl. */
	typedef typename Impl::CPUPol CPUPol;
	typedef typename Impl::DynInst DynInst;
	typedef typename Impl::DynInstPtr DynInstPtr;
	typedef typename Impl::O3CPU O3CPU;

	/** Typedefs from the CPU policy. */
	typedef typename CPUPol::FetchStruct FetchStruct;
	typedef typename CPUPol::TimeStruct TimeStruct;

	/** Typedefs from ISA. */
	typedef TheISA::MachInst MachInst;

	class FetchTranslation : public BaseTLB::Translation
	{
	protected:
	DefaultFetch<Impl> *fetch;

	public:
	FetchTranslation(DefaultFetch<Impl> *_fetch)
	: fetch(_fetch)
	{}

	void
	markDelayed()
	{}

	void
	finish(const Fault &fault, const RequestPtr &req, ThreadContext *tc,
	BaseTLB::Mode mode)
	{
	assert(mode == BaseTLB::Execute);
	fetch->finishTranslation(fault, req);
	delete this;
	}
	};

	private:
	/* Event to delay delivery of a fetch translation result in case of
	* a fault and the nop to carry the fault cannot be generated
	* immediately */
	class FinishTranslationEvent : public Event
	{
	private:
	DefaultFetch<Impl> *fetch;
	Fault fault;
	RequestPtr req;

	public:
	FinishTranslationEvent(DefaultFetch<Impl> *_fetch)
	: fetch(_fetch), req(nullptr)
	{}

	void setFault(Fault _fault)
	{
	fault = _fault;
	}

	void setReq(const RequestPtr &_req)
	{
	req = _req;
	}

	/** Process the delayed finish translation */
	void process()
	{
	assert(fetch->numInst < fetch->fetchWidth);
	fetch->finishTranslation(fault, req);
	}

	const char *description() const
	{
	return "FullO3CPU FetchFinishTranslation";
	}
	};

	public:
	/** Overall fetch status. Used to determine if the CPU can
	* deschedule itsef due to a lack of activity.
	*/
	enum FetchStatus {
	Active,
	Inactive
	};

	/** Individual thread status. */
	enum ThreadStatus {
	Running,
	Idle,
	Squashing,
	Blocked,
	Fetching,
	TrapPending,
	QuiescePending,
	ItlbWait,
	IcacheWaitResponse,
	IcacheWaitRetry,
	IcacheAccessComplete,
	NoGoodAddr
	};

	/** Fetching Policy, Add new policies here.*/
	enum FetchPriority {
	SingleThread,
	RoundRobin,
	Branch,
	IQ,
	LSQ
	};

	private:
	/** Fetch status. */
	FetchStatus _status;

	/** Per-thread status. */
	ThreadStatus fetchStatus[Impl::MaxThreads];

	/** Fetch policy. */
	FetchPriority fetchPolicy;

	/** List that has the threads organized by priority. */
	std::list<ThreadID> priorityList;

	/** Probe points. */
	ProbePointArg<DynInstPtr> *ppFetch;
	/** To probe when a fetch request is successfully sent. */
	ProbePointArg<RequestPtr> *ppFetchRequestSent;

	public:
	/** DefaultFetch constructor. */
	DefaultFetch(O3CPU _cpu, DerivO3CPUParams params);

	/** Returns the name of fetch. */
	std::string name() const;

	/** Registers statistics. */
	void regStats();

	/** Registers probes. */
	void regProbePoints();

	/** Sets the main backwards communication time buffer pointer. */
	void setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer);

	/** Sets pointer to list of active threads. */
	void setActiveThreads(std::list<ThreadID> *at_ptr);

	/** Sets pointer to time buffer used to communicate to the next stage. */
	void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);

	/** Initialize stage. */
	void startupStage();

	/** Handles retrying the fetch access. */
	void recvReqRetry();

	/** Processes cache completion event. */
	void processCacheCompletion(PacketPtr pkt);

	/** Resume after a drain. */
	void drainResume();

	/** Perform sanity checks after a drain. */
	void drainSanityCheck() const;

	/** Has the stage drained? */
	bool isDrained() const;

	/** Takes over from another CPU's thread. */
	void takeOverFrom();

	/**
	* Stall the fetch stage after reaching a safe drain point.
	*
	* The CPU uses this method to stop fetching instructions from a
	* thread that has been drained. The drain stall is different from
	* all other stalls in that it is signaled instantly from the
	* commit stage (without the normal communication delay) when it
	* has reached a safe point to drain from.
	*/
	void drainStall(ThreadID tid);

	/** Tells fetch to wake up from a quiesce instruction. */
	void wakeFromQuiesce();

	/** For priority-based fetch policies, need to keep update priorityList */
	void deactivateThread(ThreadID tid);
	private:
	/** Reset this pipeline stage */
	void resetStage();

	/** Changes the status of this stage to active, and indicates this
	* to the CPU.
	*/
	inline void switchToActive();

	/** Changes the status of this stage to inactive, and indicates
	* this to the CPU.
	*/
	inline void switchToInactive();

	/**
	* Looks up in the branch predictor to see if the next PC should be
	* either next PC+=MachInst or a branch target.
	* @param next_PC Next PC variable passed in by reference. It is
	* expected to be set to the current PC; it will be updated with what
	* the next PC will be.
	* @param next_NPC Used for ISAs which use delay slots.
	* @return Whether or not a branch was predicted as taken.
	*/
	bool lookupAndUpdateNextPC(const DynInstPtr &inst, TheISA::PCState &pc);

	/**
	* Fetches the cache line that contains the fetch PC. Returns any
	* fault that happened. Puts the data into the class variable
	* fetchBuffer, which may not hold the entire fetched cache line.
	* @param vaddr The memory address that is being fetched from.
	* @param ret_fault The fault reference that will be set to the result of
	* the icache access.
	* @param tid Thread id.
	* @param pc The actual PC of the current instruction.
	* @return Any fault that occured.
	*/
	bool fetchCacheLine(Addr vaddr, ThreadID tid, Addr pc);
	void finishTranslation(const Fault &fault, const RequestPtr &mem_req);


	/** Check if an interrupt is pending and that we need to handle
	*/
	bool
	checkInterrupt(Addr pc)
	{
	return (interruptPending && (THE_ISA != ALPHA_ISA \|\| !(pc & 0x3)));
	}

	/** Squashes a specific thread and resets the PC. */
	inline void doSquash(const TheISA::PCState &newPC,
	const DynInstPtr squashInst, ThreadID tid);

	/** Squashes a specific thread and resets the PC. Also tells the CPU to
	* remove any instructions between fetch and decode that should be sqaushed.
	*/
	void squashFromDecode(const TheISA::PCState &newPC,
	const DynInstPtr squashInst,
	const InstSeqNum seq_num, ThreadID tid);

	/** Checks if a thread is stalled. */
	bool checkStall(ThreadID tid) const;

	/** Updates overall fetch stage status; to be called at the end of each
	* cycle. */
	FetchStatus updateFetchStatus();

	public:
	/** Squashes a specific thread and resets the PC. Also tells the CPU to
	* remove any instructions that are not in the ROB. The source of this
	* squash should be the commit stage.
	*/
	void squash(const TheISA::PCState &newPC, const InstSeqNum seq_num,
	DynInstPtr squashInst, ThreadID tid);

	/** Ticks the fetch stage, processing all inputs signals and fetching
	* as many instructions as possible.
	*/
	void tick();

	/** Checks all input signals and updates the status as necessary.
	* @return: Returns if the status has changed due to input signals.
	*/
	bool checkSignalsAndUpdate(ThreadID tid);

	/** Does the actual fetching of instructions and passing them on to the
	* next stage.
	* @param status_change fetch() sets this variable if there was a status
	* change (ie switching to IcacheMissStall).
	*/
	void fetch(bool &status_change);

	/** Align a PC to the start of a fetch buffer block. */
	Addr fetchBufferAlignPC(Addr addr)
	{
	return (addr & ~(fetchBufferMask));
	}

	/** The decoder. */
	TheISA::Decoder *decoder[Impl::MaxThreads];

	private:
	DynInstPtr buildInst(ThreadID tid, StaticInstPtr staticInst,
	StaticInstPtr curMacroop, TheISA::PCState thisPC,
	TheISA::PCState nextPC, bool trace);

	/** Returns the appropriate thread to fetch, given the fetch policy. */
	ThreadID getFetchingThread(FetchPriority &fetch_priority);

	/** Returns the appropriate thread to fetch using a round robin policy. */
	ThreadID roundRobin();

	/** Returns the appropriate thread to fetch using the IQ count policy. */
	ThreadID iqCount();

	/** Returns the appropriate thread to fetch using the LSQ count policy. */
	ThreadID lsqCount();

	/** Returns the appropriate thread to fetch using the branch count
	* policy. */
	ThreadID branchCount();

	/** Pipeline the next I-cache access to the current one. */
	void pipelineIcacheAccesses(ThreadID tid);

	/** Profile the reasons of fetch stall. */
	void profileStall(ThreadID tid);

	private:
	/** Pointer to the O3CPU. */
	O3CPU *cpu;

	/** Time buffer interface. */
	TimeBuffer<TimeStruct> *timeBuffer;

	/** Wire to get decode's information from backwards time buffer. */
	typename TimeBuffer<TimeStruct>::wire fromDecode;

	/** Wire to get rename's information from backwards time buffer. */
	typename TimeBuffer<TimeStruct>::wire fromRename;

	/** Wire to get iew's information from backwards time buffer. */
	typename TimeBuffer<TimeStruct>::wire fromIEW;

	/** Wire to get commit's information from backwards time buffer. */
	typename TimeBuffer<TimeStruct>::wire fromCommit;

	//Might be annoying how this name is different than the queue.
	/** Wire used to write any information heading to decode. */
	typename TimeBuffer<FetchStruct>::wire toDecode;

	/** BPredUnit. */
	BPredUnit *branchPred;

	TheISA::PCState pc[Impl::MaxThreads];

	Addr fetchOffset[Impl::MaxThreads];

	StaticInstPtr macroop[Impl::MaxThreads];

	/** Can the fetch stage redirect from an interrupt on this instruction? */
	bool delayedCommit[Impl::MaxThreads];

	/** Memory request used to access cache. */
	RequestPtr memReq[Impl::MaxThreads];

	/** Variable that tracks if fetch has written to the time buffer this
	* cycle. Used to tell CPU if there is activity this cycle.
	*/
	bool wroteToTimeBuffer;

	/** Tracks how many instructions has been fetched this cycle. */
	int numInst;

	/** Source of possible stalls. */
	struct Stalls {
	bool decode;
	bool drain;
	};

	/** Tracks which stages are telling fetch to stall. */
	Stalls stalls[Impl::MaxThreads];

	/** Decode to fetch delay. */
	Cycles decodeToFetchDelay;

	/** Rename to fetch delay. */
	Cycles renameToFetchDelay;

	/** IEW to fetch delay. */
	Cycles iewToFetchDelay;

	/** Commit to fetch delay. */
	Cycles commitToFetchDelay;

	/** The width of fetch in instructions. */
	unsigned fetchWidth;

	/** The width of decode in instructions. */
	unsigned decodeWidth;

	/** Is the cache blocked? If so no threads can access it. */
	bool cacheBlocked;

	/** The packet that is waiting to be retried. */
	PacketPtr retryPkt;

	/** The thread that is waiting on the cache to tell fetch to retry. */
	ThreadID retryTid;

	/** Cache block size. */
	unsigned int cacheBlkSize;

	/** The size of the fetch buffer in bytes. The fetch buffer
	* itself may be smaller than a cache line.
	*/
	unsigned fetchBufferSize;

	/** Mask to align a fetch address to a fetch buffer boundary. */
	Addr fetchBufferMask;

	/** The fetch data that is being fetched and buffered. */
	uint8_t *fetchBuffer[Impl::MaxThreads];

	/** The PC of the first instruction loaded into the fetch buffer. */
	Addr fetchBufferPC[Impl::MaxThreads];

	/** The size of the fetch queue in micro-ops */
	unsigned fetchQueueSize;

	/** Queue of fetched instructions. Per-thread to prevent HoL blocking. */
	std::deque<DynInstPtr> fetchQueue[Impl::MaxThreads];

	/** Whether or not the fetch buffer data is valid. */
	bool fetchBufferValid[Impl::MaxThreads];

	/** Size of instructions. */
	int instSize;

	/** Icache stall statistics. */
	Counter lastIcacheStall[Impl::MaxThreads];

	/** List of Active Threads */
	std::list<ThreadID> *activeThreads;

	/** Number of threads. */
	ThreadID numThreads;

	/** Number of threads that are actively fetching. */
	ThreadID numFetchingThreads;

	/** Thread ID being fetched. */
	ThreadID threadFetched;

	/** Checks if there is an interrupt pending. If there is, fetch
	* must stop once it is not fetching PAL instructions.
	*/
	bool interruptPending;

	/** Set to true if a pipelined I-cache request should be issued. */
	bool issuePipelinedIfetch[Impl::MaxThreads];

	/** Event used to delay fault generation of translation faults */
	FinishTranslationEvent finishTranslationEvent;

	// @todo: Consider making these vectors and tracking on a per thread basis.
	/** Stat for total number of cycles stalled due to an icache miss. */
	Stats::Scalar icacheStallCycles;
	/** Stat for total number of fetched instructions. */
	Stats::Scalar fetchedInsts;
	/** Total number of fetched branches. */
	Stats::Scalar fetchedBranches;
	/** Stat for total number of predicted branches. */
	Stats::Scalar predictedBranches;
	/** Stat for total number of cycles spent fetching. */
	Stats::Scalar fetchCycles;
	/** Stat for total number of cycles spent squashing. */
	Stats::Scalar fetchSquashCycles;
	/** Stat for total number of cycles spent waiting for translation */
	Stats::Scalar fetchTlbCycles;
	/** Stat for total number of cycles spent blocked due to other stages in
	* the pipeline.
	*/
	Stats::Scalar fetchIdleCycles;
	/** Total number of cycles spent blocked. */
	Stats::Scalar fetchBlockedCycles;
	/** Total number of cycles spent in any other state. */
	Stats::Scalar fetchMiscStallCycles;
	/** Total number of cycles spent in waiting for drains. */
	Stats::Scalar fetchPendingDrainCycles;
	/** Total number of stall cycles caused by no active threads to run. */
	Stats::Scalar fetchNoActiveThreadStallCycles;
	/** Total number of stall cycles caused by pending traps. */
	Stats::Scalar fetchPendingTrapStallCycles;
	/** Total number of stall cycles caused by pending quiesce instructions. */
	Stats::Scalar fetchPendingQuiesceStallCycles;
	/** Total number of stall cycles caused by I-cache wait retrys. */
	Stats::Scalar fetchIcacheWaitRetryStallCycles;
	/** Stat for total number of fetched cache lines. */
	Stats::Scalar fetchedCacheLines;
	/** Total number of outstanding icache accesses that were dropped
	* due to a squash.
	*/
	Stats::Scalar fetchIcacheSquashes;
	/** Total number of outstanding tlb accesses that were dropped
	* due to a squash.
	*/
	Stats::Scalar fetchTlbSquashes;
	/** Distribution of number of instructions fetched each cycle. */
	Stats::Distribution fetchNisnDist;
	/** Rate of how often fetch was idle. */
	Stats::Formula idleRate;
	/** Number of branch fetches per cycle. */
	Stats::Formula branchRate;
	/** Number of instruction fetched per cycle. */
	Stats::Formula fetchRate;
	};

	#endif //__CPU_O3_FETCH_HH__