src/mem/cache/cache_blk.hh - public/gem5 - Git at Google

 /*
  * Copyright (c) 2012-2018 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) 2020 Inria
  * Copyright (c) 2003-2005 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.
  */

 /** @file
  * Definitions of a simple cache block class.
  */

 #ifndef __MEM_CACHE_CACHE_BLK_HH__
 #define __MEM_CACHE_CACHE_BLK_HH__

 #include <cassert>
 #include <cstdint>
 #include <iosfwd>
 #include <list>
 #include <string>

 #include "base/printable.hh"
 #include "base/types.hh"
 #include "mem/cache/tags/tagged_entry.hh"
 #include "mem/packet.hh"
 #include "mem/request.hh"
 #include "sim/cur_tick.hh"

 namespace gem5
 {

 /**
  * A Basic Cache block.
  * Contains information regarding its coherence, prefetching status, as
  * well as a pointer to its data.
  */
 class CacheBlk : public TaggedEntry
 {
   public:
     /**
      * Cache block's enum listing the supported coherence bits. The valid
      * bit is not defined here because it is part of a TaggedEntry.
      */
     enum CoherenceBits : unsigned
     {
         /** write permission */
         WritableBit =       0x02,
         /**
          * Read permission. Note that a block can be valid but not readable
          * if there is an outstanding write upgrade miss.
          */
         ReadableBit =       0x04,
         /** dirty (modified) */
         DirtyBit =          0x08,

         /**
          * Helper enum value that includes all other bits. Whenever a new
          * bits is added, this should be updated.
          */
         AllBits  =          0x0E,
     };

     /**
      * Contains a copy of the data in this block for easy access. This is used
      * for efficient execution when the data could be actually stored in
      * another format (COW, compressed, sub-blocked, etc). In all cases the
      * data stored here should be kept consistant with the actual data
      * referenced by this block.
      */
     uint8_t *data;

     /**
      * Which curTick() will this block be accessible. Its value is only
      * meaningful if the block is valid.
      */
     Tick whenReady;

   protected:
     /**
      * Represents that the indicated thread context has a "lock" on
      * the block, in the LL/SC sense.
      */
     class Lock
     {
       public:
         ContextID contextId;     // locking context
         Addr lowAddr;      // low address of lock range
         Addr highAddr;     // high address of lock range

         // check for matching execution context, and an address that
         // is within the lock
         bool matches(const RequestPtr &req) const
         {
             Addr req_low = req->getPaddr();
             Addr req_high = req_low + req->getSize() -1;
             return (contextId == req->contextId()) &&
                    (req_low >= lowAddr) && (req_high <= highAddr);
         }

         // check if a request is intersecting and thus invalidating the lock
         bool intersects(const RequestPtr &req) const
         {
             Addr req_low = req->getPaddr();
             Addr req_high = req_low + req->getSize() - 1;

             return (req_low <= highAddr) && (req_high >= lowAddr);
         }

         Lock(const RequestPtr &req)
             : contextId(req->contextId()),
               lowAddr(req->getPaddr()),
               highAddr(lowAddr + req->getSize() - 1)
         {
         }
     };

     /** List of thread contexts that have performed a load-locked (LL)
      * on the block since the last store. */
     std::list<Lock> lockList;

   public:
     CacheBlk() : TaggedEntry(), data(nullptr), _tickInserted(0)
     {
         invalidate();
     }

     CacheBlk(const CacheBlk&) = delete;
     CacheBlk& operator=(const CacheBlk&) = delete;
     CacheBlk(const CacheBlk&&) = delete;
     /**
      * Move assignment operator.
      * This should only be used to move an existing valid entry into an
      * invalid one, not to create a new entry. In the end the valid entry
      * will become invalid, and the invalid, valid. All location related
      * variables will remain the same, that is, an entry cannot move its
      * data, just its metadata contents.
      */
     virtual CacheBlk&
     operator=(CacheBlk&& other)
     {
         // Copying an entry into a valid one would imply in skipping all
         // replacement steps, so it cannot be allowed
         assert(!isValid());
         assert(other.isValid());

         insert(other.getTag(), other.isSecure());

         if (other.wasPrefetched()) {
             setPrefetched();
         }
         setCoherenceBits(other.coherence);
         setTaskId(other.getTaskId());
         setWhenReady(curTick());
         setRefCount(other.getRefCount());
         setSrcRequestorId(other.getSrcRequestorId());
         std::swap(lockList, other.lockList);

         other.invalidate();

         return *this;
     }
     virtual ~CacheBlk() {};

     /**
      * Invalidate the block and clear all state.
      */
     virtual void invalidate() override
     {
         TaggedEntry::invalidate();

         clearPrefetched();
         clearCoherenceBits(AllBits);

         setTaskId(context_switch_task_id::Unknown);
         setWhenReady(MaxTick);
         setRefCount(0);
         setSrcRequestorId(Request::invldRequestorId);
         lockList.clear();
     }

     /**
      * Sets the corresponding coherence bits.
      *
      * @param bits The coherence bits to be set.
      */
     void
     setCoherenceBits(unsigned bits)
     {
         assert(isValid());
         coherence |= bits;
     }

     /**
      * Clear the corresponding coherence bits.
      *
      * @param bits The coherence bits to be cleared.
      */
     void clearCoherenceBits(unsigned bits) { coherence &= ~bits; }

     /**
      * Checks the given coherence bits are set.
      *
      * @return True if the block is readable.
      */
     bool
     isSet(unsigned bits) const
     {
         return isValid() && (coherence & bits);
     }

     /**
      * Check if this block was the result of a hardware prefetch, yet to
      * be touched.
      * @return True if the block was a hardware prefetch, unaccesed.
      */
     bool wasPrefetched() const { return _prefetched; }

     /**
      * Clear the prefetching bit. Either because it was recently used, or due
      * to the block being invalidated.
      */
     void clearPrefetched() { _prefetched = false; }

     /** Marks this blocks as a recently prefetched block. */
     void setPrefetched() { _prefetched = true; }

     /**
      * Get tick at which block's data will be available for access.
      *
      * @return Data ready tick.
      */
     Tick getWhenReady() const
     {
         assert(whenReady != MaxTick);
         return whenReady;
     }

     /**
      * Set tick at which block's data will be available for access. The new
      * tick must be chronologically sequential with respect to previous
      * accesses.
      *
      * @param tick New data ready tick.
      */
     void setWhenReady(const Tick tick)
     {
         assert(tick >= _tickInserted);
         whenReady = tick;
     }

     /** Get the task id associated to this block. */
     uint32_t getTaskId() const { return _taskId; }

     /** Get the requestor id associated to this block. */
     uint32_t getSrcRequestorId() const { return _srcRequestorId; }

     /** Get the number of references to this block since insertion. */
     unsigned getRefCount() const { return _refCount; }

     /** Get the number of references to this block since insertion. */
     void increaseRefCount() { _refCount++; }

     /**
      * Get the block's age, that is, the number of ticks since its insertion.
      *
      * @return The block's age.
      */
     Tick
     getAge() const
     {
         assert(_tickInserted <= curTick());
         return curTick() - _tickInserted;
     }

     /**
      * Set member variables when a block insertion occurs. Resets reference
      * count to 1 (the insertion counts as a reference), and touch block if
      * it hadn't been touched previously. Sets the insertion tick to the
      * current tick. Marks the block valid.
      *
      * @param tag Block address tag.
      * @param is_secure Whether the block is in secure space or not.
      * @param src_requestor_ID The source requestor ID.
      * @param task_ID The new task ID.
      */
     void insert(const Addr tag, const bool is_secure,
         const int src_requestor_ID, const uint32_t task_ID);
     using TaggedEntry::insert;

     /**
      * Track the fact that a local locked was issued to the
      * block. Invalidate any previous LL to the same address.
      */
     void trackLoadLocked(PacketPtr pkt)
     {
         assert(pkt->isLLSC());
         auto l = lockList.begin();
         while (l != lockList.end()) {
             if (l->intersects(pkt->req))
                 l = lockList.erase(l);
             else
                 ++l;
         }

         lockList.emplace_front(pkt->req);
     }

     /**
      * Clear the any load lock that intersect the request, and is from
      * a different context.
      */
     void clearLoadLocks(const RequestPtr &req)
     {
         auto l = lockList.begin();
         while (l != lockList.end()) {
             if (l->intersects(req) && l->contextId != req->contextId()) {
                 l = lockList.erase(l);
             } else {
                 ++l;
             }
         }
     }

     /**
      * Pretty-print tag, set and way, and interpret state bits to readable form
      * including mapping to a MOESI state.
      *
      * @return string with basic state information
      */
     std::string
     print() const override
     {
         /**
          *  state       M   O   E   S   I
          *  writable    1   0   1   0   0
          *  dirty       1   1   0   0   0
          *  valid       1   1   1   1   0
          *
          *  state   writable    dirty   valid
          *  M       1           1       1
          *  O       0           1       1
          *  E       1           0       1
          *  S       0           0       1
          *  I       0           0       0
          *
          * Note that only one cache ever has a block in Modified or
          * Owned state, i.e., only one cache owns the block, or
          * equivalently has the DirtyBit bit set. However, multiple
          * caches on the same path to memory can have a block in the
          * Exclusive state (despite the name). Exclusive means this
          * cache has the only copy at this level of the hierarchy,
          * i.e., there may be copies in caches above this cache (in
          * various states), but there are no peers that have copies on
          * this branch of the hierarchy, and no caches at or above
          * this level on any other branch have copies either.
          **/
         unsigned state =
             isSet(WritableBit) << 2 | isSet(DirtyBit) << 1 | isValid();
         char s = '?';
         switch (state) {
           case 0b111: s = 'M'; break;
           case 0b011: s = 'O'; break;
           case 0b101: s = 'E'; break;
           case 0b001: s = 'S'; break;
           case 0b000: s = 'I'; break;
           default:    s = 'T'; break; // @TODO add other types
         }
         return csprintf("state: %x (%c) writable: %d readable: %d "
             "dirty: %d prefetched: %d | %s", coherence, s,
             isSet(WritableBit), isSet(ReadableBit), isSet(DirtyBit),
             wasPrefetched(), TaggedEntry::print());
     }

     /**
      * Handle interaction of load-locked operations and stores.
      * @return True if write should proceed, false otherwise.  Returns
      * false only in the case of a failed store conditional.
      */
     bool checkWrite(PacketPtr pkt)
     {
         assert(pkt->isWrite());

         // common case
         if (!pkt->isLLSC() && lockList.empty())
             return true;

         const RequestPtr &req = pkt->req;

         if (pkt->isLLSC()) {
             // it's a store conditional... have to check for matching
             // load locked.
             bool success = false;

             auto l = lockList.begin();
             while (!success && l != lockList.end()) {
                 if (l->matches(pkt->req)) {
                     // it's a store conditional, and as far as the
                     // memory system can tell, the requesting
                     // context's lock is still valid.
                     success = true;
                     lockList.erase(l);
                 } else {
                     ++l;
                 }
             }

             req->setExtraData(success ? 1 : 0);
             // clear any intersected locks from other contexts (our LL
             // should already have cleared them)
             clearLoadLocks(req);
             return success;
         } else {
             // a normal write, if there is any lock not from this
             // context we clear the list, thus for a private cache we
             // never clear locks on normal writes
             clearLoadLocks(req);
             return true;
         }
     }

   protected:
     /** The current coherence status of this block. @sa CoherenceBits */
     unsigned coherence;

     // The following setters have been marked as protected because their
     // respective variables should only be modified at 2 moments:
     // invalidation and insertion. Because of that, they shall only be
     // called by the functions that perform those actions.

     /** Set the task id value. */
     void setTaskId(const uint32_t task_id) { _taskId = task_id; }

     /** Set the source requestor id. */
     void setSrcRequestorId(const uint32_t id) { _srcRequestorId = id; }

     /** Set the number of references to this block since insertion. */
     void setRefCount(const unsigned count) { _refCount = count; }

     /** Set the current tick as this block's insertion tick. */
     void setTickInserted() { _tickInserted = curTick(); }

   private:
     /** Task Id associated with this block */
     uint32_t _taskId;

     /** holds the source requestor ID for this block. */
     int _srcRequestorId;

     /** Number of references to this block since it was brought in. */
     unsigned _refCount;

     /**
      * Tick on which the block was inserted in the cache. Its value is only
      * meaningful if the block is valid.
      */
     Tick _tickInserted;

     /** Whether this block is an unaccessed hardware prefetch. */
     bool _prefetched;
 };

 /**
  * Special instance of CacheBlk for use with tempBlk that deals with its
  * block address regeneration.
  * @sa Cache
  */
 class TempCacheBlk final : public CacheBlk
 {
   private:
     /**
      * Copy of the block's address, used to regenerate tempBlock's address.
      */
     Addr _addr;

   public:
     /**
      * Creates a temporary cache block, with its own storage.
      * @param size The size (in bytes) of this cache block.
      */
     TempCacheBlk(unsigned size) : CacheBlk()
     {
         data = new uint8_t[size];
     }
     TempCacheBlk(const TempCacheBlk&) = delete;
     TempCacheBlk& operator=(const TempCacheBlk&) = delete;
     ~TempCacheBlk() { delete [] data; };

     /**
      * Invalidate the block and clear all state.
      */
     void invalidate() override {
         CacheBlk::invalidate();

         _addr = MaxAddr;
     }

     void
     insert(const Addr addr, const bool is_secure) override
     {
         CacheBlk::insert(addr, is_secure);
         _addr = addr;
     }

     /**
      * Get block's address.
      *
      * @return addr Address value.
      */
     Addr getAddr() const
     {
         return _addr;
     }
 };

 /**
  * Simple class to provide virtual print() method on cache blocks
  * without allocating a vtable pointer for every single cache block.
  * Just wrap the CacheBlk object in an instance of this before passing
  * to a function that requires a Printable object.
  */
 class CacheBlkPrintWrapper : public Printable
 {
     CacheBlk *blk;
   public:
     CacheBlkPrintWrapper(CacheBlk *_blk) : blk(_blk) {}
     virtual ~CacheBlkPrintWrapper() {}
     void print(std::ostream &o, int verbosity = 0,
                const std::string &prefix = "") const;
 };

 } // namespace gem5

 #endif //__MEM_CACHE_CACHE_BLK_HH__
	/*
	* Copyright (c) 2012-2018 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) 2020 Inria
	* Copyright (c) 2003-2005 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.
	*/

	/** @file
	* Definitions of a simple cache block class.
	*/

	#ifndef __MEM_CACHE_CACHE_BLK_HH__
	#define __MEM_CACHE_CACHE_BLK_HH__

	#include <cassert>
	#include <cstdint>
	#include <iosfwd>
	#include <list>
	#include <string>

	#include "base/printable.hh"
	#include "base/types.hh"
	#include "mem/cache/tags/tagged_entry.hh"
	#include "mem/packet.hh"
	#include "mem/request.hh"
	#include "sim/cur_tick.hh"

	namespace gem5
	{

	/**
	* A Basic Cache block.
	* Contains information regarding its coherence, prefetching status, as
	* well as a pointer to its data.
	*/
	class CacheBlk : public TaggedEntry
	{
	public:
	/**
	* Cache block's enum listing the supported coherence bits. The valid
	* bit is not defined here because it is part of a TaggedEntry.
	*/
	enum CoherenceBits : unsigned
	{
	/** write permission */
	WritableBit = 0x02,
	/**
	* Read permission. Note that a block can be valid but not readable
	* if there is an outstanding write upgrade miss.
	*/
	ReadableBit = 0x04,
	/** dirty (modified) */
	DirtyBit = 0x08,

	/**
	* Helper enum value that includes all other bits. Whenever a new
	* bits is added, this should be updated.
	*/
	AllBits = 0x0E,
	};

	/**
	* Contains a copy of the data in this block for easy access. This is used
	* for efficient execution when the data could be actually stored in
	* another format (COW, compressed, sub-blocked, etc). In all cases the
	* data stored here should be kept consistant with the actual data
	* referenced by this block.
	*/
	uint8_t *data;

	/**
	* Which curTick() will this block be accessible. Its value is only
	* meaningful if the block is valid.
	*/
	Tick whenReady;

	protected:
	/**
	* Represents that the indicated thread context has a "lock" on
	* the block, in the LL/SC sense.
	*/
	class Lock
	{
	public:
	ContextID contextId; // locking context
	Addr lowAddr; // low address of lock range
	Addr highAddr; // high address of lock range

	// check for matching execution context, and an address that
	// is within the lock
	bool matches(const RequestPtr &req) const
	{
	Addr req_low = req->getPaddr();
	Addr req_high = req_low + req->getSize() -1;
	return (contextId == req->contextId()) &&
	(req_low >= lowAddr) && (req_high <= highAddr);
	}

	// check if a request is intersecting and thus invalidating the lock
	bool intersects(const RequestPtr &req) const
	{
	Addr req_low = req->getPaddr();
	Addr req_high = req_low + req->getSize() - 1;

	return (req_low <= highAddr) && (req_high >= lowAddr);
	}

	Lock(const RequestPtr &req)
	: contextId(req->contextId()),
	lowAddr(req->getPaddr()),
	highAddr(lowAddr + req->getSize() - 1)
	{
	}
	};

	/** List of thread contexts that have performed a load-locked (LL)
	* on the block since the last store. */
	std::list<Lock> lockList;

	public:
	CacheBlk() : TaggedEntry(), data(nullptr), _tickInserted(0)
	{
	invalidate();
	}

	CacheBlk(const CacheBlk&) = delete;
	CacheBlk& operator=(const CacheBlk&) = delete;
	CacheBlk(const CacheBlk&&) = delete;
	/**
	* Move assignment operator.
	* This should only be used to move an existing valid entry into an
	* invalid one, not to create a new entry. In the end the valid entry
	* will become invalid, and the invalid, valid. All location related
	* variables will remain the same, that is, an entry cannot move its
	* data, just its metadata contents.
	*/
	virtual CacheBlk&
	operator=(CacheBlk&& other)
	{
	// Copying an entry into a valid one would imply in skipping all
	// replacement steps, so it cannot be allowed
	assert(!isValid());
	assert(other.isValid());

	insert(other.getTag(), other.isSecure());

	if (other.wasPrefetched()) {
	setPrefetched();
	}
	setCoherenceBits(other.coherence);
	setTaskId(other.getTaskId());
	setWhenReady(curTick());
	setRefCount(other.getRefCount());
	setSrcRequestorId(other.getSrcRequestorId());
	std::swap(lockList, other.lockList);

	other.invalidate();

	return *this;
	}
	virtual ~CacheBlk() {};

	/**
	* Invalidate the block and clear all state.
	*/
	virtual void invalidate() override
	{
	TaggedEntry::invalidate();

	clearPrefetched();
	clearCoherenceBits(AllBits);

	setTaskId(context_switch_task_id::Unknown);
	setWhenReady(MaxTick);
	setRefCount(0);
	setSrcRequestorId(Request::invldRequestorId);
	lockList.clear();
	}

	/**
	* Sets the corresponding coherence bits.
	*
	* @param bits The coherence bits to be set.
	*/
	void
	setCoherenceBits(unsigned bits)
	{
	assert(isValid());
	coherence \|= bits;
	}

	/**
	* Clear the corresponding coherence bits.
	*
	* @param bits The coherence bits to be cleared.
	*/
	void clearCoherenceBits(unsigned bits) { coherence &= ~bits; }

	/**
	* Checks the given coherence bits are set.
	*
	* @return True if the block is readable.
	*/
	bool
	isSet(unsigned bits) const
	{
	return isValid() && (coherence & bits);
	}

	/**
	* Check if this block was the result of a hardware prefetch, yet to
	* be touched.
	* @return True if the block was a hardware prefetch, unaccesed.
	*/
	bool wasPrefetched() const { return _prefetched; }

	/**
	* Clear the prefetching bit. Either because it was recently used, or due
	* to the block being invalidated.
	*/
	void clearPrefetched() { _prefetched = false; }

	/** Marks this blocks as a recently prefetched block. */
	void setPrefetched() { _prefetched = true; }

	/**
	* Get tick at which block's data will be available for access.
	*
	* @return Data ready tick.
	*/
	Tick getWhenReady() const
	{
	assert(whenReady != MaxTick);
	return whenReady;
	}

	/**
	* Set tick at which block's data will be available for access. The new
	* tick must be chronologically sequential with respect to previous
	* accesses.
	*
	* @param tick New data ready tick.
	*/
	void setWhenReady(const Tick tick)
	{
	assert(tick >= _tickInserted);
	whenReady = tick;
	}

	/** Get the task id associated to this block. */
	uint32_t getTaskId() const { return _taskId; }

	/** Get the requestor id associated to this block. */
	uint32_t getSrcRequestorId() const { return _srcRequestorId; }

	/** Get the number of references to this block since insertion. */
	unsigned getRefCount() const { return _refCount; }

	/** Get the number of references to this block since insertion. */
	void increaseRefCount() { _refCount++; }

	/**
	* Get the block's age, that is, the number of ticks since its insertion.
	*
	* @return The block's age.
	*/
	Tick
	getAge() const
	{
	assert(_tickInserted <= curTick());
	return curTick() - _tickInserted;
	}

	/**
	* Set member variables when a block insertion occurs. Resets reference
	* count to 1 (the insertion counts as a reference), and touch block if
	* it hadn't been touched previously. Sets the insertion tick to the
	* current tick. Marks the block valid.
	*
	* @param tag Block address tag.
	* @param is_secure Whether the block is in secure space or not.
	* @param src_requestor_ID The source requestor ID.
	* @param task_ID The new task ID.
	*/
	void insert(const Addr tag, const bool is_secure,
	const int src_requestor_ID, const uint32_t task_ID);
	using TaggedEntry::insert;

	/**
	* Track the fact that a local locked was issued to the
	* block. Invalidate any previous LL to the same address.
	*/
	void trackLoadLocked(PacketPtr pkt)
	{
	assert(pkt->isLLSC());
	auto l = lockList.begin();
	while (l != lockList.end()) {
	if (l->intersects(pkt->req))
	l = lockList.erase(l);
	else
	++l;
	}

	lockList.emplace_front(pkt->req);
	}

	/**
	* Clear the any load lock that intersect the request, and is from
	* a different context.
	*/
	void clearLoadLocks(const RequestPtr &req)
	{
	auto l = lockList.begin();
	while (l != lockList.end()) {
	if (l->intersects(req) && l->contextId != req->contextId()) {
	l = lockList.erase(l);
	} else {
	++l;
	}
	}
	}

	/**
	* Pretty-print tag, set and way, and interpret state bits to readable form
	* including mapping to a MOESI state.
	*
	* @return string with basic state information
	*/
	std::string
	print() const override
	{
	/**
	* state M O E S I
	* writable 1 0 1 0 0
	* dirty 1 1 0 0 0
	* valid 1 1 1 1 0
	*
	* state writable dirty valid
	* M 1 1 1
	* O 0 1 1
	* E 1 0 1
	* S 0 0 1
	* I 0 0 0
	*
	* Note that only one cache ever has a block in Modified or
	* Owned state, i.e., only one cache owns the block, or
	* equivalently has the DirtyBit bit set. However, multiple
	* caches on the same path to memory can have a block in the
	* Exclusive state (despite the name). Exclusive means this
	* cache has the only copy at this level of the hierarchy,
	* i.e., there may be copies in caches above this cache (in
	* various states), but there are no peers that have copies on
	* this branch of the hierarchy, and no caches at or above
	* this level on any other branch have copies either.
	**/
	unsigned state =
	isSet(WritableBit) << 2 \| isSet(DirtyBit) << 1 \| isValid();
	char s = '?';
	switch (state) {
	case 0b111: s = 'M'; break;
	case 0b011: s = 'O'; break;
	case 0b101: s = 'E'; break;
	case 0b001: s = 'S'; break;
	case 0b000: s = 'I'; break;
	default: s = 'T'; break; // @TODO add other types
	}
	return csprintf("state: %x (%c) writable: %d readable: %d "
	"dirty: %d prefetched: %d \| %s", coherence, s,
	isSet(WritableBit), isSet(ReadableBit), isSet(DirtyBit),
	wasPrefetched(), TaggedEntry::print());
	}

	/**
	* Handle interaction of load-locked operations and stores.
	* @return True if write should proceed, false otherwise. Returns
	* false only in the case of a failed store conditional.
	*/
	bool checkWrite(PacketPtr pkt)
	{
	assert(pkt->isWrite());

	// common case
	if (!pkt->isLLSC() && lockList.empty())
	return true;

	const RequestPtr &req = pkt->req;

	if (pkt->isLLSC()) {
	// it's a store conditional... have to check for matching
	// load locked.
	bool success = false;

	auto l = lockList.begin();
	while (!success && l != lockList.end()) {
	if (l->matches(pkt->req)) {
	// it's a store conditional, and as far as the
	// memory system can tell, the requesting
	// context's lock is still valid.
	success = true;
	lockList.erase(l);
	} else {
	++l;
	}
	}

	req->setExtraData(success ? 1 : 0);
	// clear any intersected locks from other contexts (our LL
	// should already have cleared them)
	clearLoadLocks(req);
	return success;
	} else {
	// a normal write, if there is any lock not from this
	// context we clear the list, thus for a private cache we
	// never clear locks on normal writes
	clearLoadLocks(req);
	return true;
	}
	}

	protected:
	/** The current coherence status of this block. @sa CoherenceBits */
	unsigned coherence;

	// The following setters have been marked as protected because their
	// respective variables should only be modified at 2 moments:
	// invalidation and insertion. Because of that, they shall only be
	// called by the functions that perform those actions.

	/** Set the task id value. */
	void setTaskId(const uint32_t task_id) { _taskId = task_id; }

	/** Set the source requestor id. */
	void setSrcRequestorId(const uint32_t id) { _srcRequestorId = id; }

	/** Set the number of references to this block since insertion. */
	void setRefCount(const unsigned count) { _refCount = count; }

	/** Set the current tick as this block's insertion tick. */
	void setTickInserted() { _tickInserted = curTick(); }

	private:
	/** Task Id associated with this block */
	uint32_t _taskId;

	/** holds the source requestor ID for this block. */
	int _srcRequestorId;

	/** Number of references to this block since it was brought in. */
	unsigned _refCount;

	/**
	* Tick on which the block was inserted in the cache. Its value is only
	* meaningful if the block is valid.
	*/
	Tick _tickInserted;

	/** Whether this block is an unaccessed hardware prefetch. */
	bool _prefetched;
	};

	/**
	* Special instance of CacheBlk for use with tempBlk that deals with its
	* block address regeneration.
	* @sa Cache
	*/
	class TempCacheBlk final : public CacheBlk
	{
	private:
	/**
	* Copy of the block's address, used to regenerate tempBlock's address.
	*/
	Addr _addr;

	public:
	/**
	* Creates a temporary cache block, with its own storage.
	* @param size The size (in bytes) of this cache block.
	*/
	TempCacheBlk(unsigned size) : CacheBlk()
	{
	data = new uint8_t[size];
	}
	TempCacheBlk(const TempCacheBlk&) = delete;
	TempCacheBlk& operator=(const TempCacheBlk&) = delete;
	~TempCacheBlk() { delete [] data; };

	/**
	* Invalidate the block and clear all state.
	*/
	void invalidate() override {
	CacheBlk::invalidate();

	_addr = MaxAddr;
	}

	void
	insert(const Addr addr, const bool is_secure) override
	{
	CacheBlk::insert(addr, is_secure);
	_addr = addr;
	}

	/**
	* Get block's address.
	*
	* @return addr Address value.
	*/
	Addr getAddr() const
	{
	return _addr;
	}
	};

	/**
	* Simple class to provide virtual print() method on cache blocks
	* without allocating a vtable pointer for every single cache block.
	* Just wrap the CacheBlk object in an instance of this before passing
	* to a function that requires a Printable object.
	*/
	class CacheBlkPrintWrapper : public Printable
	{
	CacheBlk *blk;
	public:
	CacheBlkPrintWrapper(CacheBlk *_blk) : blk(_blk) {}
	virtual ~CacheBlkPrintWrapper() {}
	void print(std::ostream &o, int verbosity = 0,
	const std::string &prefix = "") const;
	};

	} // namespace gem5

	#endif //__MEM_CACHE_CACHE_BLK_HH__