src/cpu/inorder/cpu.hh

/*
 * Copyright (c) 2012-2013 ARM Limited
 * Copyright (c) 2013 Advanced Micro Devices, Inc.
 * 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) 2007 MIPS Technologies, Inc.
 * 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: Korey Sewell
 *
 */

#ifndef __CPU_INORDER_CPU_HH__
#define __CPU_INORDER_CPU_HH__

#include <iostream>
#include <list>
#include <queue>
#include <set>
#include <vector>

#include "arch/isa_traits.hh"
#include "arch/registers.hh"
#include "arch/types.hh"
#include "base/statistics.hh"
#include "base/types.hh"
#include "config/the_isa.hh"
#include "cpu/inorder/inorder_dyn_inst.hh"
#include "cpu/inorder/pipeline_stage.hh"
#include "cpu/inorder/pipeline_traits.hh"
#include "cpu/inorder/reg_dep_map.hh"
#include "cpu/inorder/thread_state.hh"
#include "cpu/o3/dep_graph.hh"
#include "cpu/o3/rename_map.hh"
#include "cpu/activity.hh"
#include "cpu/base.hh"
#include "cpu/reg_class.hh"
#include "cpu/simple_thread.hh"
#include "cpu/timebuf.hh"
#include "mem/packet.hh"
#include "mem/port.hh"
#include "mem/request.hh"
#include "sim/eventq.hh"
#include "sim/process.hh"

class CacheUnit;
class ThreadContext;
class MemInterface;
class MemObject;
class Process;
class ResourcePool;

class InOrderCPU : public BaseCPU
{

  protected:
    typedef ThePipeline::Params Params;
    typedef InOrderThreadState Thread;

   //ISA TypeDefs
    typedef TheISA::IntReg IntReg;
    typedef TheISA::FloatReg FloatReg;
    typedef TheISA::FloatRegBits FloatRegBits;
    typedef TheISA::CCReg CCReg;
    typedef TheISA::MiscReg MiscReg;
    typedef TheISA::RegIndex RegIndex;

    //DynInstPtr TypeDefs
    typedef ThePipeline::DynInstPtr DynInstPtr;
    typedef std::list<DynInstPtr>::iterator ListIt;

    //TimeBuffer TypeDefs
    typedef TimeBuffer<InterStageStruct> StageQueue;

    friend class Resource;
    
  public:
    /** Constructs a CPU with the given parameters. */
    InOrderCPU(Params *params);
    /* Destructor */
    ~InOrderCPU();
    
    void verifyMemoryMode() const;

    /** Return a reference to the data port. */
    virtual MasterPort &getDataPort() { return dataPort; }

    /** Return a reference to the instruction port. */
    virtual MasterPort &getInstPort() { return instPort; }

    /** CPU ID */
    int cpu_id;

    // SE Mode ASIDs
    ThreadID asid[ThePipeline::MaxThreads];

    /** Type of core that this is */
    std::string coreType;

    // Only need for SE MODE
    enum ThreadModel {
        Single,
        SMT,
        SwitchOnCacheMiss
    };
    
    ThreadModel threadModel;

    int readCpuId() { return cpu_id; }

    void setCpuId(int val) { cpu_id = val; }

    Params *cpu_params;

  public:
    enum Status {
        Running,
        Idle,
        Halted,
        Blocked,
        SwitchedOut
    };

    /** Overall CPU status. */
    Status _status;
  private:

    /**
     * CachePort class for the in-order CPU, interacting with a
     * specific CacheUnit in the pipeline.
     */
    class CachePort : public MasterPort
    {

      private:
        /** Pointer to cache unit */
        CacheUnit *cacheUnit;

      public:
        /** Default constructor. */
        CachePort(CacheUnit *_cacheUnit, const std::string& name);

      protected:

        /** Timing version of receive */
        bool recvTimingResp(PacketPtr pkt);

        /** Handles doing a retry of a failed timing request. */
        void recvRetry();

        /** Ignoring snoops for now. */
        void recvTimingSnoopReq(PacketPtr pkt) { }
    };

    /** Define TickEvent for the CPU */
    class TickEvent : public Event
    {
      private:
        /** Pointer to the CPU. */
        InOrderCPU *cpu;

      public:
        /** Constructs a tick event. */
        TickEvent(InOrderCPU *c);

        /** Processes a tick event, calling tick() on the CPU. */
        void process();

        /** Returns the description of the tick event. */
        const char *description() const;
    };

    /** The tick event used for scheduling CPU ticks. */
    TickEvent tickEvent;

    /** Schedule tick event, regardless of its current state. */
    void scheduleTickEvent(Cycles delay)
    {
        assert(!tickEvent.scheduled() || tickEvent.squashed());
        reschedule(&tickEvent, clockEdge(delay), true);
    }

    /** Unschedule tick event, regardless of its current state. */
    void unscheduleTickEvent()
    {
        if (tickEvent.scheduled())
            tickEvent.squash();
    }

  public:
    // List of Events That can be scheduled from
    // within the CPU.
    // NOTE(1): The Resource Pool also uses this event list
    // to schedule events broadcast to all resources interfaces
    // NOTE(2): CPU Events usually need to schedule a corresponding resource
    // pool event.
    enum CPUEventType {
        ActivateThread,
        ActivateNextReadyThread,
        DeactivateThread,
        HaltThread,
        SuspendThread,
        Trap,
        Syscall,
        SquashFromMemStall,
        UpdatePCs,
        NumCPUEvents
    };

    static std::string eventNames[NumCPUEvents];

    enum CPUEventPri {
        InOrderCPU_Pri                 = Event::CPU_Tick_Pri,
        Syscall_Pri                    = Event::CPU_Tick_Pri + 9,
        ActivateNextReadyThread_Pri    = Event::CPU_Tick_Pri + 10
    };

    /** Define CPU Event */
    class CPUEvent : public Event
    {
      protected:
        InOrderCPU *cpu;

      public:
        CPUEventType cpuEventType;
        ThreadID tid;
        DynInstPtr inst;
        Fault fault;
        unsigned vpe;
        short syscall_num;
        
      public:
        /** Constructs a CPU event. */
        CPUEvent(InOrderCPU *_cpu, CPUEventType e_type, const Fault &fault,
                 ThreadID _tid, DynInstPtr inst, CPUEventPri event_pri);

        /** Set Type of Event To Be Scheduled */
        void setEvent(CPUEventType e_type, const Fault &_fault, ThreadID _tid,
                      DynInstPtr _inst)
        {
            fault = _fault;
            cpuEventType = e_type;
            tid = _tid;
            inst = _inst;
            vpe = 0;            
        }

        /** Processes a CPU event. */
        void process();

        /** Returns the description of the CPU event. */
        const char *description() const;

        /** Schedule Event */
        void scheduleEvent(Cycles delay);

        /** Unschedule This Event */
        void unscheduleEvent();
    };

    /** Schedule a CPU Event */
    void scheduleCpuEvent(CPUEventType cpu_event, const Fault &fault,
                          ThreadID tid,
                          DynInstPtr inst, Cycles delay = Cycles(0),
                          CPUEventPri event_pri = InOrderCPU_Pri);

  public:

    /** Width (processing bandwidth) of each stage */
    int stageWidth;

    /** Interface between the CPU and CPU resources. */
    ResourcePool *resPool;

    /** Instruction used to signify that there is no *real* instruction in 
        buffer slot */
    DynInstPtr dummyInst[ThePipeline::MaxThreads];
    DynInstPtr dummyBufferInst;
    DynInstPtr dummyReqInst;
    DynInstPtr dummyTrapInst[ThePipeline::MaxThreads];

    /** Used by resources to signify a denied access to a resource. */
    ResourceRequest *dummyReq[ThePipeline::MaxThreads];

    /** The Pipeline Stages for the CPU */
    PipelineStage *pipelineStage[ThePipeline::NumStages];

    /** Program Counters */
    TheISA::PCState pc[ThePipeline::MaxThreads];

    /** Last Committed PC */
    TheISA::PCState lastCommittedPC[ThePipeline::MaxThreads];

    /** The Register File for the CPU */
    union {
        FloatReg f[ThePipeline::MaxThreads][TheISA::NumFloatRegs];
        FloatRegBits i[ThePipeline::MaxThreads][TheISA::NumFloatRegs];
    } floatRegs;
    TheISA::IntReg intRegs[ThePipeline::MaxThreads][TheISA::NumIntRegs];
#ifdef ISA_HAS_CC_REGS
    TheISA::CCReg ccRegs[ThePipeline::MaxThreads][TheISA::NumCCRegs];
#endif

    /** ISA state */
    std::vector<TheISA::ISA *> isa;

    /** Dependency Tracker for Integer & Floating Point Regs */
    RegDepMap archRegDepMap[ThePipeline::MaxThreads];

    /** Global communication structure */
    TimeBuffer<TimeStruct> timeBuffer;

    /** Communication structure that sits in between pipeline stages */
    StageQueue *stageQueue[ThePipeline::NumStages-1];

    TheISA::TLB *getITBPtr();
    TheISA::TLB *getDTBPtr();

    TheISA::Decoder *getDecoderPtr(unsigned tid);

    /** Accessor Type for the SkedCache */
    typedef uint32_t SkedID;

    /** Cache of Instruction Schedule using the instruction's name as a key */
    static m5::hash_map<SkedID, ThePipeline::RSkedPtr> skedCache;

    typedef m5::hash_map<SkedID, ThePipeline::RSkedPtr>::iterator SkedCacheIt;

    /** Initialized to last iterator in map, signifying a invalid entry
        on map searches
    */
    SkedCacheIt endOfSkedIt;

    ThePipeline::RSkedPtr frontEndSked;
    ThePipeline::RSkedPtr faultSked;

    /** Add a new instruction schedule to the schedule cache */
    void addToSkedCache(DynInstPtr inst, ThePipeline::RSkedPtr inst_sked)
    {
        SkedID sked_id = genSkedID(inst);
        assert(skedCache.find(sked_id) == skedCache.end());
        skedCache[sked_id] = inst_sked;
    }


    /** Find a instruction schedule */
    ThePipeline::RSkedPtr lookupSked(DynInstPtr inst)
    {
        SkedID sked_id = genSkedID(inst);
        SkedCacheIt lookup_it = skedCache.find(sked_id);

        if (lookup_it != endOfSkedIt) {
            return (*lookup_it).second;
        } else {
            return NULL;
        }
    }

    static const uint8_t INST_OPCLASS                       = 26;
    static const uint8_t INST_LOAD                          = 25;
    static const uint8_t INST_STORE                         = 24;
    static const uint8_t INST_CONTROL                       = 23;
    static const uint8_t INST_NONSPEC                       = 22;
    static const uint8_t INST_DEST_REGS                     = 18;
    static const uint8_t INST_SRC_REGS                      = 14;
    static const uint8_t INST_SPLIT_DATA                    = 13;

    inline SkedID genSkedID(DynInstPtr inst)
    {
        SkedID id = 0;
        id = (inst->opClass() << INST_OPCLASS) |
            (inst->isLoad() << INST_LOAD) |
            (inst->isStore() << INST_STORE) |
            (inst->isControl() << INST_CONTROL) |
            (inst->isNonSpeculative() << INST_NONSPEC) |
            (inst->numDestRegs() << INST_DEST_REGS) |
            (inst->numSrcRegs() << INST_SRC_REGS) |
            (inst->splitInst << INST_SPLIT_DATA);
        return id;
    }

    ThePipeline::RSkedPtr createFrontEndSked();
    ThePipeline::RSkedPtr createFaultSked();
    ThePipeline::RSkedPtr createBackEndSked(DynInstPtr inst);

    class StageScheduler {
      private:
        ThePipeline::RSkedPtr rsked;
        int stageNum;
        int nextTaskPriority;

      public:
        StageScheduler(ThePipeline::RSkedPtr _rsked, int stage_num)
            : rsked(_rsked), stageNum(stage_num),
              nextTaskPriority(0)
        { }

        void needs(int unit, int request) {
            rsked->push(new ScheduleEntry(
                            stageNum, nextTaskPriority++, unit, request
                            ));
        }

        void needs(int unit, int request, int param) {
            rsked->push(new ScheduleEntry(
                            stageNum, nextTaskPriority++, unit, request, param
                            ));
        }
    };

  private:

    /** Data port. Note that it has to appear after the resPool. */
    CachePort dataPort;

    /** Instruction port. Note that it has to appear after the resPool. */
    CachePort instPort;

  public:

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

    /** Ticks CPU, calling tick() on each stage, and checking the overall
     *  activity to see if the CPU should deschedule itself.
     */
    void tick();

    /** Initialize the CPU */
    void init();

    /** HW return from error interrupt. */
    Fault hwrei(ThreadID tid);

    bool simPalCheck(int palFunc, ThreadID tid);

    void checkForInterrupts();

    /** Returns the Fault for any valid interrupt. */
    Fault getInterrupts();

    /** Processes any an interrupt fault. */
    void processInterrupts(const Fault &interrupt);

    /** Halts the CPU. */
    void halt() { panic("Halt not implemented!\n"); }

    /** Check if this address is a valid instruction address. */
    bool validInstAddr(Addr addr) { return true; }

    /** Check if this address is a valid data address. */
    bool validDataAddr(Addr addr) { return true; }

    /** Schedule a syscall on the CPU */
    void syscallContext(const Fault &fault, ThreadID tid, DynInstPtr inst,
                        Cycles delay = Cycles(0));

    /** Executes a syscall.*/
    void syscall(int64_t callnum, ThreadID tid);

    /** Schedule a trap on the CPU */
    void trapContext(const Fault &fault, ThreadID tid, DynInstPtr inst,
                     Cycles delay = Cycles(0));

    /** Perform trap to Handle Given Fault */
    void trap(const Fault &fault, ThreadID tid, DynInstPtr inst);

    /** Schedule thread activation on the CPU */
    void activateContext(ThreadID tid);

    /** Add Thread to Active Threads List. */
    void activateThread(ThreadID tid);

    /** Activate Thread In Each Pipeline Stage */
    void activateThreadInPipeline(ThreadID tid);
    
    /** Schedule Thread Activation from Ready List */
    void activateNextReadyContext();

    /** Add Thread From Ready List to Active Threads List. */
    void activateNextReadyThread();

    /** Schedule a thread deactivation on the CPU */
    void deactivateContext(ThreadID tid);

    /** Remove from Active Thread List */
    void deactivateThread(ThreadID tid);

    /** Schedule a thread suspension on the CPU */
  void suspendContext(ThreadID tid);

    /** Suspend Thread, Remove from Active Threads List, Add to Suspend List */
    void suspendThread(ThreadID tid);

    /** Schedule a thread halt on the CPU */
    void haltContext(ThreadID tid);

    /** Halt Thread, Remove from Active Thread List, Place Thread on Halted 
     *  Threads List 
     */
    void haltThread(ThreadID tid);

    /** squashFromMemStall() - sets up a squash event
     *  squashDueToMemStall() - squashes pipeline
     *  @note: maybe squashContext/squashThread would be better?
     */
    void squashFromMemStall(DynInstPtr inst, ThreadID tid,
                            Cycles delay = Cycles(0));
    void squashDueToMemStall(int stage_num, InstSeqNum seq_num, ThreadID tid);    

    void removePipelineStalls(ThreadID tid);
    void squashThreadInPipeline(ThreadID tid);
    void squashBehindMemStall(int stage_num, InstSeqNum seq_num, ThreadID tid);    

    PipelineStage* getPipeStage(int stage_num);

    int
    contextId()
    {
        hack_once("return a bogus context id");
        return 0;
    }

    /** Update The Order In Which We Process Threads. */
    void updateThreadPriority();

    /** Switches a Pipeline Stage to Active. (Unused currently) */
    void switchToActive(int stage_idx)
    { /*pipelineStage[stage_idx]->switchToActive();*/ }

    /** Get the current instruction sequence number, and increment it. */
    InstSeqNum getAndIncrementInstSeq(ThreadID tid)
    { return globalSeqNum[tid]++; }

    /** Get the current instruction sequence number, and increment it. */
    InstSeqNum nextInstSeqNum(ThreadID tid)
    { return globalSeqNum[tid]; }

    /** Increment Instruction Sequence Number */
    void incrInstSeqNum(ThreadID tid)
    { globalSeqNum[tid]++; }

    /** Set Instruction Sequence Number */
    void setInstSeqNum(ThreadID tid, InstSeqNum seq_num)
    {
        globalSeqNum[tid] = seq_num;
    }

    /** Get & Update Next Event Number */
    InstSeqNum getNextEventNum()
    {
#ifdef DEBUG
        return cpuEventNum++;
#else
        return 0;
#endif
    }

    /** Register file accessors  */
    uint64_t readIntReg(RegIndex reg_idx, ThreadID tid);

    FloatReg readFloatReg(RegIndex reg_idx, ThreadID tid);

    FloatRegBits readFloatRegBits(RegIndex reg_idx, ThreadID tid);

    CCReg readCCReg(RegIndex reg_idx, ThreadID tid);

    void setIntReg(RegIndex reg_idx, uint64_t val, ThreadID tid);

    void setFloatReg(RegIndex reg_idx, FloatReg val, ThreadID tid);

    void setFloatRegBits(RegIndex reg_idx, FloatRegBits val,  ThreadID tid);

    void setCCReg(RegIndex reg_idx, CCReg val, ThreadID tid);

    RegIndex flattenRegIdx(RegIndex reg_idx, RegClass &reg_type, ThreadID tid);

    /** Reads a miscellaneous register. */
    MiscReg readMiscRegNoEffect(int misc_reg, ThreadID tid = 0);

    /** Reads a misc. register, including any side effects the read
     * might have as defined by the architecture.
     */
    MiscReg readMiscReg(int misc_reg, ThreadID tid = 0);

    /** Sets a miscellaneous register. */
    void setMiscRegNoEffect(int misc_reg, const MiscReg &val,
                            ThreadID tid = 0);

    /** Sets a misc. register, including any side effects the write
     * might have as defined by the architecture.
     */
    void setMiscReg(int misc_reg, const MiscReg &val, ThreadID tid = 0);

    /** Reads a int/fp/misc reg. from another thread depending on ISA-defined
     *  target thread
     */
    uint64_t readRegOtherThread(unsigned misc_reg,
                                ThreadID tid = InvalidThreadID);

    /** Sets a int/fp/misc reg. from another thread depending on an ISA-defined
     * target thread
     */
    void setRegOtherThread(unsigned misc_reg, const MiscReg &val,
                           ThreadID tid);

    /** Reads the commit PC of a specific thread. */
    TheISA::PCState
    pcState(ThreadID tid)
    {
        return pc[tid];
    }

    /** Sets the commit PC of a specific thread. */
    void
    pcState(const TheISA::PCState &newPC, ThreadID tid)
    {
        pc[tid] = newPC;
    }

    Addr instAddr(ThreadID tid) { return pc[tid].instAddr(); }
    Addr nextInstAddr(ThreadID tid) { return pc[tid].nextInstAddr(); }
    MicroPC microPC(ThreadID tid) { return pc[tid].microPC(); }

    /** Function to add instruction onto the head of the list of the
     *  instructions.  Used when new instructions are fetched.
     */
    ListIt addInst(DynInstPtr inst);

    /** Find instruction on instruction list */
    ListIt findInst(InstSeqNum seq_num, ThreadID tid);

    /** Function to tell the CPU that an instruction has completed. */
    void instDone(DynInstPtr inst, ThreadID tid);

    /** Add Instructions to the CPU Remove List*/
    void addToRemoveList(DynInstPtr inst);

    /** Remove an instruction from CPU */
    void removeInst(DynInstPtr inst);

    /** Remove all instructions younger than the given sequence number. */
    void removeInstsUntil(const InstSeqNum &seq_num,ThreadID tid);

    /** Removes the instruction pointed to by the iterator. */
    inline void squashInstIt(const ListIt inst_it, ThreadID tid);

    /** Cleans up all instructions on the instruction remove list. */
    void cleanUpRemovedInsts();

    /** Cleans up all events on the CPU event remove list. */
    void cleanUpRemovedEvents();

    /** Debug function to print all instructions on the list. */
    void dumpInsts();

    /** Forwards an instruction read to the appropriate data
     *  resource (indexes into Resource Pool thru "dataPortIdx")
     */
    Fault read(DynInstPtr inst, Addr addr,
               uint8_t *data, unsigned size, unsigned flags);

    /** Forwards an instruction write. to the appropriate data
     *  resource (indexes into Resource Pool thru "dataPortIdx")
     */
    Fault write(DynInstPtr inst, uint8_t *data, unsigned size,
                Addr addr, unsigned flags, uint64_t *write_res = NULL);

  public:
    /** Per-Thread List of all the instructions in flight. */
    std::list<DynInstPtr> instList[ThePipeline::MaxThreads];

    /** List of all the instructions that will be removed at the end of this
     *  cycle.
     */
    std::queue<ListIt> removeList;

    bool trapPending[ThePipeline::MaxThreads];

    /** List of all the cpu event requests that will be removed at the end of
     *  the current cycle.
     */
    std::queue<Event*> cpuEventRemoveList;

    /** Records if instructions need to be removed this cycle due to
     *  being retired or squashed.
     */
    bool removeInstsThisCycle;

    /** True if there is non-speculative Inst Active In Pipeline. Lets any
     * execution unit know, NOT to execute while the instruction is active.
     */
    bool nonSpecInstActive[ThePipeline::MaxThreads];

    /** Instruction Seq. Num of current non-speculative instruction. */
    InstSeqNum nonSpecSeqNum[ThePipeline::MaxThreads];

    /** Instruction Seq. Num of last instruction squashed in pipeline */
    InstSeqNum squashSeqNum[ThePipeline::MaxThreads];

    /** Last Cycle that the CPU squashed instruction end. */
    Tick lastSquashCycle[ThePipeline::MaxThreads];

    std::list<ThreadID> fetchPriorityList;

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

    /** Ready Threads List */
    std::list<ThreadID> readyThreads;

    /** Suspended Threads List */
    std::list<ThreadID> suspendedThreads;

    /** Halted Threads List */
    std::list<ThreadID> haltedThreads;

    /** Thread Status Functions */
    bool isThreadActive(ThreadID tid);
    bool isThreadReady(ThreadID tid);
    bool isThreadSuspended(ThreadID tid);

  private:
    /** The activity recorder; used to tell if the CPU has any
     * activity remaining or if it can go to idle and deschedule
     * itself.
     */
    ActivityRecorder activityRec;

  public:
    /** Number of Active Threads in the CPU */
    ThreadID numActiveThreads() { return activeThreads.size(); }

    /** Thread id of active thread
     *  Only used for SwitchOnCacheMiss model. 
     *  Assumes only 1 thread active
     */
    ThreadID activeThreadId() 
    { 
        if (numActiveThreads() > 0)
            return activeThreads.front();
        else
            return InvalidThreadID;
    }
    
     
    /** Records that there was time buffer activity this cycle. */
    void activityThisCycle() { activityRec.activity(); }

    /** Changes a stage's status to active within the activity recorder. */
    void activateStage(const int idx)
    { activityRec.activateStage(idx); }

    /** Changes a stage's status to inactive within the activity recorder. */
    void deactivateStage(const int idx)
    { activityRec.deactivateStage(idx); }

    /** Wakes the CPU, rescheduling the CPU if it's not already active. */
    void wakeCPU();

    virtual void wakeup();

    /* LL/SC debug functionality
    unsigned stCondFails;

    unsigned readStCondFailures() 
    { return stCondFails; }

    unsigned setStCondFailures(unsigned st_fails) 
    { return stCondFails = st_fails; }
    */

    /** Returns a pointer to a thread context. */
    ThreadContext *tcBase(ThreadID tid = 0)
    {
        return thread[tid]->getTC();
    }

    /** Count the Total Instructions Committed in the CPU. */
    virtual Counter totalInsts() const
    {
        Counter total(0);

        for (ThreadID tid = 0; tid < (ThreadID)thread.size(); tid++)
            total += thread[tid]->numInst;

        return total;
    }

    /** Count the Total Ops Committed in the CPU. */
    virtual Counter totalOps() const
    {
        Counter total(0);

        for (ThreadID tid = 0; tid < (ThreadID)thread.size(); tid++)
            total += thread[tid]->numOp;

        return total;
    }

    /** Pointer to the system. */
    System *system;

    /** The global sequence number counter. */
    InstSeqNum globalSeqNum[ThePipeline::MaxThreads];

#ifdef DEBUG
    /** The global event number counter. */
    InstSeqNum cpuEventNum;

    /** Number of resource requests active in CPU **/
    unsigned resReqCount;
#endif

    Addr lockAddr;

    /** Temporary fix for the lock flag, works in the UP case. */
    bool lockFlag;

    /** Counter of how many stages have completed draining */
    int drainCount;

    /** Pointers to all of the threads in the CPU. */
    std::vector<Thread *> thread;

    /** Per-Stage Instruction Tracing */
    bool stageTracing;

    /** The cycle that the CPU was last running, used for statistics. */
    Tick lastRunningCycle;

    void updateContextSwitchStats();    
    unsigned instsPerSwitch;    
    Stats::Average instsPerCtxtSwitch;    
    Stats::Scalar numCtxtSwitches;
    
    /** Resumes execution after a drain. */
    void drainResume();

    /** Switches out this CPU. */
    virtual void switchOut();

    /** Takes over from another CPU. */
    virtual void takeOverFrom(BaseCPU *oldCPU);

    /** Update Thread , used for statistic purposes*/
    inline void tickThreadStats();

    /** Per-Thread Tick */
    Stats::Vector threadCycles;

    /** Tick for SMT */
    Stats::Scalar smtCycles;

    /** Stat for total number of times the CPU is descheduled. */
    Stats::Scalar timesIdled;

    /** Stat for total number of cycles the CPU spends descheduled or no
     *  stages active.
     */
    Stats::Scalar idleCycles;

    /** Stat for total number of cycles the CPU is active. */
    Stats::Scalar runCycles;

    /** Percentage of cycles a stage was active */
    Stats::Formula activity;

    /** Instruction Mix Stats */
    Stats::Scalar comLoads;
    Stats::Scalar comStores;
    Stats::Scalar comBranches;
    Stats::Scalar comNops;
    Stats::Scalar comNonSpec;
    Stats::Scalar comInts;
    Stats::Scalar comFloats;

    /** Stat for the number of committed instructions per thread. */
    Stats::Vector committedInsts;

    /** Stat for the number of committed ops per thread. */
    Stats::Vector committedOps;

    /** Stat for the number of committed instructions per thread. */
    Stats::Vector smtCommittedInsts;

    /** Stat for the total number of committed instructions. */
    Stats::Scalar totalCommittedInsts;

    /** Stat for the CPI per thread. */
    Stats::Formula cpi;

    /** Stat for the SMT-CPI per thread. */
    Stats::Formula smtCpi;

    /** Stat for the total CPI. */
    Stats::Formula totalCpi;

    /** Stat for the IPC per thread. */
    Stats::Formula ipc;

    /** Stat for the total IPC. */
    Stats::Formula smtIpc;

    /** Stat for the total IPC. */
    Stats::Formula totalIpc;
};

#endif // __CPU_O3_CPU_HH__