src/cpu/minor/buffers.hh - public/gem5 - Git at Google

 /*
  * Copyright (c) 2013-2014 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.
  *
  * 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
  *
  * Classes for buffer, queue and FIFO behaviour.
  */

 #ifndef __CPU_MINOR_BUFFERS_HH__
 #define __CPU_MINOR_BUFFERS_HH__

 #include <iostream>
 #include <queue>
 #include <sstream>
 #include <string>

 #include "base/logging.hh"
 #include "base/named.hh"
 #include "base/types.hh"
 #include "cpu/activity.hh"
 #include "cpu/minor/trace.hh"
 #include "cpu/timebuf.hh"

 namespace gem5
 {

 GEM5_DEPRECATED_NAMESPACE(Minor, minor);
 namespace minor
 {

 /** Interface class for data with reporting/tracing facilities.  This
  *  interface doesn't actually have to be used as other classes which need
  *  this interface uses templating rather than inheritance but it's provided
  *  here to document the interface needed by those classes. */
 class ReportIF
 {
   public:
     /** Print the data in a format suitable to be the value in "name=value"
      *  trace lines */
     virtual void reportData(std::ostream &os) const = 0;

     virtual ~ReportIF() { }
 };

 /** Interface class for data with 'bubble' values.  This interface doesn't
  *  actually have to be used as other classes which need this interface uses
  *  templating rather than inheritance but it's provided here to document
  *  the interface needed by those classes. */
 class BubbleIF
 {
   public:
     virtual bool isBubble() const = 0;
 };

 /** ...ReportTraits are trait classes with the same functionality as
  *  ReportIF, but with elements explicitly passed into the report...
  *  functions. */

 /** Allow a template using ReportTraits to call report... functions of
  *  ReportIF-bearing elements themselves */
 template <typename ElemType> /* ElemType should implement ReportIF */
 class ReportTraitsAdaptor
 {
   public:
     static void
     reportData(std::ostream &os, const ElemType &elem)
     { elem.reportData(os); }
 };

 /** A similar adaptor but for elements held by pointer
  *  ElemType should implement ReportIF */
 template <typename PtrType>
 class ReportTraitsPtrAdaptor
 {
   public:
     static void
     reportData(std::ostream &os, const PtrType &elem)
     { elem->reportData(os); }
 };

 /** ... BubbleTraits are trait classes to add BubbleIF interface
  *  functionality to templates which process elements which don't necessarily
  *  implement BubbleIF themselves */

 /** Default behaviour, no bubbles */
 template <typename ElemType>
 class NoBubbleTraits
 {
   public:
     static bool isBubble(const ElemType &) { return false; }
     static ElemType
     bubble()
     {
         panic("bubble called but no bubble interface");
     }
 };

 /** Pass on call to the element */
 template <typename ElemType>
 class BubbleTraitsAdaptor
 {
   public:
     static bool isBubble(const ElemType &elem)
     { return elem.isBubble(); }

     static ElemType bubble() { return ElemType::bubble(); }
 };

 /** Pass on call to the element where the element is a pointer */
 template <typename PtrType, typename ElemType>
 class BubbleTraitsPtrAdaptor
 {
   public:
     static bool isBubble(const PtrType &elem)
     { return elem->isBubble(); }

     static PtrType bubble() { return ElemType::bubble(); }
 };

 /** TimeBuffer with MinorTrace and Named interfaces */
 template <typename ElemType,
     typename ReportTraits = ReportTraitsAdaptor<ElemType>,
     typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
 class MinorBuffer : public Named, public TimeBuffer<ElemType>
 {
   protected:
     /** The range of elements that should appear in trace lines */
     int reportLeft, reportRight;

     /** Name to use for the data in a MinorTrace line */
     std::string dataName;

   public:
     MinorBuffer(const std::string &name,
         const std::string &data_name,
         int num_past, int num_future,
         int report_left = -1, int report_right = -1) :
         Named(name), TimeBuffer<ElemType>(num_past, num_future),
         reportLeft(report_left), reportRight(report_right),
             dataName(data_name)
     { }

   public:
     /* Is this buffer full of only bubbles */
     bool
     empty() const
     {
         bool ret = true;

         for (int i = -this->past; i <= this->future; i++) {
             if (!BubbleTraits::isBubble((*this)[i]))
                 ret = false;
         }

         return ret;
     }

     /** Report buffer states from 'slot' 'from' to 'to'.  For example 0,-1
       * will produce two slices with current (just assigned) and last (one
       * advance() old) slices with the current (0) one on the left.
       * Reverse the numbers to change the order of slices */
     void
     minorTrace() const
     {
         std::ostringstream data;

         int step = (reportLeft > reportRight ? -1 : 1);
         int end = reportRight + step;
         int i = reportLeft;

         while (i != end) {
             const ElemType &datum = (*this)[i];

             ReportTraits::reportData(data, datum);
             i += step;
             if (i != end)
                 data << ',';
         }

         minor::minorTrace("%s=%s\n", dataName, data.str());
     }
 };

 /** Wraps a MinorBuffer with Input/Output interfaces to ensure that units
  *  within the model can only see the right end of buffers between them. */
 template <typename Data>
 class Latch
 {
   public:
     typedef MinorBuffer<Data> Buffer;

   protected:
     /** Delays, in cycles, writing data into the latch and seeing it on the
      *  latched wires */
     Cycles delay;

     Buffer buffer;

   public:
     /** forward/backwardDelay specify the delay from input to output in each
      *  direction.  These arguments *must* be >= 1 */
     Latch(const std::string &name,
         const std::string &data_name,
         Cycles delay_ = Cycles(1),
         bool report_backwards = false) :
         delay(delay_),
         buffer(name, data_name, delay_, 0, (report_backwards ? -delay_ : 0),
             (report_backwards ? 0 : -delay_))
     { }

   public:
     /** Encapsulate wires on either input or output of the latch.
      *  forward/backward correspond to data direction relative to the
      *  pipeline.  Latched and Immediate specify delay for backward data.
      *  Immediate data is available to earlier stages *during* the cycle it
      *  is written */
     class Input
     {
       public:
         typename Buffer::wire inputWire;

       public:
         Input(typename Buffer::wire input_wire) :
             inputWire(input_wire)
         { }
     };

     class Output
     {
       public:
         typename Buffer::wire outputWire;

       public:
         Output(typename Buffer::wire output_wire) :
             outputWire(output_wire)
         { }
     };

     bool empty() const { return buffer.empty(); }

     /** An interface to just the input of the buffer */
     Input input() { return Input(buffer.getWire(0)); }

     /** An interface to just the output of the buffer */
     Output output() { return Output(buffer.getWire(-delay)); }

     void minorTrace() const { buffer.minorTrace(); }

     void evaluate() { buffer.advance(); }
 };

 /** A pipeline simulating class that will stall (not advance when advance()
  *  is called) if a non-bubble value lies at the far end of the pipeline.
  *  The user can clear the stall before calling advance to unstall the
  *  pipeline. */
 template <typename ElemType,
     typename ReportTraits,
     typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
 class SelfStallingPipeline : public MinorBuffer<ElemType, ReportTraits>
 {
   protected:
     /** Wire at the input end of the pipeline (for convenience) */
     typename TimeBuffer<ElemType>::wire pushWire;
     /** Wire at the output end of the pipeline (for convenience) */
     typename TimeBuffer<ElemType>::wire popWire;

   public:
     /** If true, advance will not advance the pipeline */
     bool stalled;

     /** The number of slots with non-bubbles in them */
     unsigned int occupancy;

   public:
     SelfStallingPipeline(const std::string &name,
         const std::string &data_name,
         unsigned depth) :
         MinorBuffer<ElemType, ReportTraits>
             (name, data_name, depth, 0, -1, -depth),
         pushWire(this->getWire(0)),
         popWire(this->getWire(-depth)),
         stalled(false),
         occupancy(0)
     {
         assert(depth > 0);

         /* Write explicit bubbles to get around the case where the default
          *  constructor for the element type isn't good enough */
         for (unsigned i = 0; i <= depth; i++)
             (*this)[-i] = BubbleTraits::bubble();
     }

   public:
     /** Write an element to the back of the pipeline.  This doesn't cause
      *  the pipeline to advance until advance is called.  Pushing twice
      *  without advance-ing will just cause an overwrite of the last push's
      *  data. */
     void push(ElemType &elem)
     {
         assert(!alreadyPushed());
         *pushWire = elem;
         if (!BubbleTraits::isBubble(elem))
             occupancy++;
     }

     /** Peek at the end element of the pipe */
     ElemType &front() { return *popWire; }

     const ElemType &front() const { return *popWire; }

     /** Have we already pushed onto this pipe without advancing */
     bool alreadyPushed() { return !BubbleTraits::isBubble(*pushWire); }

     /** There's data (not a bubble) at the end of the pipe */
     bool isPopable() { return !BubbleTraits::isBubble(front()); }

     /** Try to advance the pipeline.  If we're stalled, don't advance.  If
      *  we're not stalled, advance then check to see if we become stalled
      *  (a non-bubble at the end of the pipe) */
     void
     advance()
     {
         bool data_at_end = isPopable();

         if (!stalled) {
             TimeBuffer<ElemType>::advance();
             /* If there was data at the end of the pipe that has now been
              *  advanced out of the pipe, we've lost data */
             if (data_at_end)
                 occupancy--;
             /* Is there data at the end of the pipe now? */
             stalled = isPopable();
             /* Insert a bubble into the empty input slot to make sure that
              *  element is correct in the case where the default constructor
              *  for ElemType doesn't produce a bubble */
             ElemType bubble = BubbleTraits::bubble();
             *pushWire = bubble;
         }
     }
 };

 /** Base class for space reservation requestable objects */
 class Reservable
 {
   public:
     /** Can a slot be reserved? */
     virtual bool canReserve() const = 0;

     /** Reserve a slot in whatever structure this is attached to */
     virtual void reserve() = 0;

     /** Free a reserved slot */
     virtual void freeReservation() = 0;

     virtual ~Reservable() {};
 };

 /** Wrapper for a queue type to act as a pipeline stage input queue.
  *  Handles capacity management, bubble value suppression and provides
  *  reporting.
  *
  *  In an ideal world, ElemType would be derived from ReportIF and BubbleIF,
  *  but here we use traits and allow the Adaptors ReportTraitsAdaptor and
  *  BubbleTraitsAdaptor to work on data which *does* directly implement
  *  those interfaces. */
 template <typename ElemType,
     typename ReportTraits = ReportTraitsAdaptor<ElemType>,
     typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
 class Queue : public Named, public Reservable
 {
   private:
       std::deque<ElemType> queue;

     /** Number of slots currently reserved for future (reservation
      *  respecting) pushes */
     unsigned int numReservedSlots;

     /** Need this here as queues usually don't have a limited capacity */
     unsigned int capacity;

     /** Name to use for the data in MinorTrace */
     std::string dataName;

   public:
     Queue(const std::string &name, const std::string &data_name,
         unsigned int capacity_) :
         Named(name),
         numReservedSlots(0),
         capacity(capacity_),
         dataName(data_name)
     { }

   public:
     /** Push an element into the buffer if it isn't a bubble.  Bubbles are
      *  just discarded.  It is assummed that any push into a queue with
      *  reserved space intends to take that space */
     void
     push(ElemType &data)
     {
         if (!BubbleTraits::isBubble(data)) {
             freeReservation();
             queue.push_back(data);

             if (queue.size() > capacity) {
                 warn("%s: No space to push data into queue of capacity"
                     " %u, pushing anyway\n", name(), capacity);
             }

         }
     }

     /** Clear all allocated space.  Be careful how this is used */
     void clearReservedSpace() { numReservedSlots = 0; }

     /** Clear a single reserved slot */
     void freeReservation()
     {
         if (numReservedSlots != 0)
             numReservedSlots--;
     }

     /** Reserve space in the queue for future pushes.  Enquiries about space
      *  in the queue using unreservedRemainingSpace will only tell about
      *  space which is not full and not reserved. */
     void
     reserve()
     {
         /* Check reservable space */
         if (unreservedRemainingSpace() == 0)
             warn("%s: No space is reservable in queue", name());

         numReservedSlots++;
     }

     bool canReserve() const { return unreservedRemainingSpace() != 0; }

     /** Number of slots available in an empty buffer */
     unsigned int totalSpace() const { return capacity; }

     /** Number of slots already occupied in this buffer */
     unsigned int occupiedSpace() const { return queue.size(); }

     /** Number of slots which are reserved. */
     unsigned int reservedSpace() const { return numReservedSlots; }

     /** Number of slots yet to fill in this buffer.  This doesn't include
      *  reservation. */
     unsigned int
     remainingSpace() const
     {
         int ret = capacity - queue.size();

         return (ret < 0 ? 0 : ret);
     }

     /** Like remainingSpace but does not count reserved spaces */
     unsigned int
     unreservedRemainingSpace() const
     {
         int ret = capacity - (queue.size() + numReservedSlots);

         return (ret < 0 ? 0 : ret);
     }

     /** Head value.  Like std::queue::front */
     ElemType &front() { return queue.front(); }

     const ElemType &front() const { return queue.front(); }

     /** Pop the head item.  Like std::queue::pop */
     void pop() { queue.pop_front(); }

     /** Is the queue empty? */
     bool empty() const { return queue.empty(); }

     void
     minorTrace() const
     {
         std::ostringstream data;
         /* If we become over-full, totalSpace() can actually be smaller than
          * occupiedSpace().  Handle this */
         unsigned int num_total = (occupiedSpace() > totalSpace() ?
             occupiedSpace() : totalSpace());

         unsigned int num_reserved = reservedSpace();
         unsigned int num_occupied = occupiedSpace();

         int num_printed = 1;
         /* Bodge to rotate queue to report elements */
         while (num_printed <= num_occupied) {
             ReportTraits::reportData(data, queue[num_printed - 1]);
             num_printed++;

             if (num_printed <= num_total)
                 data << ',';
         }

         int num_printed_reserved = 1;
         /* Show reserved slots */
         while (num_printed_reserved <= num_reserved &&
             num_printed <= num_total)
         {
             data << 'R';
             num_printed_reserved++;
             num_printed++;

             if (num_printed <= num_total)
                 data << ',';
         }

         /* And finally pad with empty slots (if there are any) */
         while (num_printed <= num_total) {
             num_printed++;

             if (num_printed <= num_total)
                 data << ',';
         }

         minor::minorTrace("%s=%s\n", dataName, data.str());
     }
 };

 /** Like a Queue but with a restricted interface and a setTail function
  *  which, when the queue is empty, just takes a reference to the pushed
  *  item as the single element.  Calling pushTail will push that element
  *  onto the queue.
  *
  *  The purpose of this class is to allow the faster operation of queues of
  *  items which usually don't get deeper than one item and for which the copy
  *  associated with a push is expensive enough to want to avoid
  *
  *  The intended use case is the input buffer for pipeline stages, hence the
  *  class name */
 template <typename ElemType,
     typename ReportTraits = ReportTraitsAdaptor<ElemType>,
     typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
 class InputBuffer : public Reservable
 {
   protected:
     /** Underlying queue */
     mutable Queue<ElemType, ReportTraits, BubbleTraits> queue;

     /** Pointer to the single element (if not NULL) */
     mutable ElemType *elementPtr;

   public:
     InputBuffer(const std::string &name, const std::string &data_name,
         unsigned int capacity_) :
         queue(name, data_name, capacity_),
         elementPtr(NULL)
     { }

   public:
     /** Set the tail of the queue, this is like push but needs
      *  to be followed by pushTail for the new tail to make its
      *  way into the queue proper */
     void
     setTail(ElemType &new_element)
     {
         assert(!elementPtr);
         if (!BubbleTraits::isBubble(new_element)) {
             if (queue.empty())
                 elementPtr = &new_element;
             else
                 queue.push(new_element);
         }
     }

     /** No single element or queue entries */
     bool empty() const { return !elementPtr && queue.empty(); }

     /** Return the element, or the front of the queue */
     const ElemType &front() const
     { return (elementPtr ? *elementPtr : queue.front()); }

     ElemType &front()
     { return (elementPtr ? *elementPtr : queue.front()); }

     /** Pop either the head, or if none, the head of the queue */
     void
     pop()
     {
         if (elementPtr) {
             /* A popped element was expected to be pushed into queue
              *  and so take a reserved space */
             elementPtr = NULL;
             queue.freeReservation();
         } else {
             queue.pop();
         }
     }

     /** Push the single element (if any) into the queue proper.  If the
      *  element's reference points to a transient object, remember to
      *  always do this before the end of that object's life */
     void
     pushTail() const
     {
         if (elementPtr)
             queue.push(*elementPtr);
         elementPtr = NULL;
     }

     /** Report elements */
     void
     minorTrace() const
     {
         pushTail();
         queue.minorTrace();
     }

     /** Reservable interface, passed on to queue */
     bool canReserve() const { return queue.canReserve(); }
     void reserve() { queue.reserve(); }
     void freeReservation() { queue.freeReservation(); }

     /** Like remainingSpace but does not count reserved spaces */
     unsigned int
     unreservedRemainingSpace()
     {
         pushTail();
         return queue.unreservedRemainingSpace();
     }
 };

 } // namespace minor
 } // namespace gem5

 #endif /* __CPU_MINOR_BUFFERS_HH__ */
	/*
	* Copyright (c) 2013-2014 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.
	*
	* 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
	*
	* Classes for buffer, queue and FIFO behaviour.
	*/

	#ifndef __CPU_MINOR_BUFFERS_HH__
	#define __CPU_MINOR_BUFFERS_HH__

	#include <iostream>
	#include <queue>
	#include <sstream>
	#include <string>

	#include "base/logging.hh"
	#include "base/named.hh"
	#include "base/types.hh"
	#include "cpu/activity.hh"
	#include "cpu/minor/trace.hh"
	#include "cpu/timebuf.hh"

	namespace gem5
	{

	GEM5_DEPRECATED_NAMESPACE(Minor, minor);
	namespace minor
	{

	/** Interface class for data with reporting/tracing facilities. This
	* interface doesn't actually have to be used as other classes which need
	* this interface uses templating rather than inheritance but it's provided
	* here to document the interface needed by those classes. */
	class ReportIF
	{
	public:
	/** Print the data in a format suitable to be the value in "name=value"
	* trace lines */
	virtual void reportData(std::ostream &os) const = 0;

	virtual ~ReportIF() { }
	};

	/** Interface class for data with 'bubble' values. This interface doesn't
	* actually have to be used as other classes which need this interface uses
	* templating rather than inheritance but it's provided here to document
	* the interface needed by those classes. */
	class BubbleIF
	{
	public:
	virtual bool isBubble() const = 0;
	};

	/** ...ReportTraits are trait classes with the same functionality as
	* ReportIF, but with elements explicitly passed into the report...
	* functions. */

	/** Allow a template using ReportTraits to call report... functions of
	* ReportIF-bearing elements themselves */
	template <typename ElemType> /* ElemType should implement ReportIF */
	class ReportTraitsAdaptor
	{
	public:
	static void
	reportData(std::ostream &os, const ElemType &elem)
	{ elem.reportData(os); }
	};

	/** A similar adaptor but for elements held by pointer
	* ElemType should implement ReportIF */
	template <typename PtrType>
	class ReportTraitsPtrAdaptor
	{
	public:
	static void
	reportData(std::ostream &os, const PtrType &elem)
	{ elem->reportData(os); }
	};

	/** ... BubbleTraits are trait classes to add BubbleIF interface
	* functionality to templates which process elements which don't necessarily
	* implement BubbleIF themselves */

	/** Default behaviour, no bubbles */
	template <typename ElemType>
	class NoBubbleTraits
	{
	public:
	static bool isBubble(const ElemType &) { return false; }
	static ElemType
	bubble()
	{
	panic("bubble called but no bubble interface");
	}
	};

	/** Pass on call to the element */
	template <typename ElemType>
	class BubbleTraitsAdaptor
	{
	public:
	static bool isBubble(const ElemType &elem)
	{ return elem.isBubble(); }

	static ElemType bubble() { return ElemType::bubble(); }
	};

	/** Pass on call to the element where the element is a pointer */
	template <typename PtrType, typename ElemType>
	class BubbleTraitsPtrAdaptor
	{
	public:
	static bool isBubble(const PtrType &elem)
	{ return elem->isBubble(); }

	static PtrType bubble() { return ElemType::bubble(); }
	};

	/** TimeBuffer with MinorTrace and Named interfaces */
	template <typename ElemType,
	typename ReportTraits = ReportTraitsAdaptor<ElemType>,
	typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
	class MinorBuffer : public Named, public TimeBuffer<ElemType>
	{
	protected:
	/** The range of elements that should appear in trace lines */
	int reportLeft, reportRight;

	/** Name to use for the data in a MinorTrace line */
	std::string dataName;

	public:
	MinorBuffer(const std::string &name,
	const std::string &data_name,
	int num_past, int num_future,
	int report_left = -1, int report_right = -1) :
	Named(name), TimeBuffer<ElemType>(num_past, num_future),
	reportLeft(report_left), reportRight(report_right),
	dataName(data_name)
	{ }

	public:
	/* Is this buffer full of only bubbles */
	bool
	empty() const
	{
	bool ret = true;

	for (int i = -this->past; i <= this->future; i++) {
	if (!BubbleTraits::isBubble((*this)[i]))
	ret = false;
	}

	return ret;
	}

	/** Report buffer states from 'slot' 'from' to 'to'. For example 0,-1
	* will produce two slices with current (just assigned) and last (one
	* advance() old) slices with the current (0) one on the left.
	* Reverse the numbers to change the order of slices */
	void
	minorTrace() const
	{
	std::ostringstream data;

	int step = (reportLeft > reportRight ? -1 : 1);
	int end = reportRight + step;
	int i = reportLeft;

	while (i != end) {
	const ElemType &datum = (*this)[i];

	ReportTraits::reportData(data, datum);
	i += step;
	if (i != end)
	data << ',';
	}

	minor::minorTrace("%s=%s\n", dataName, data.str());
	}
	};

	/** Wraps a MinorBuffer with Input/Output interfaces to ensure that units
	* within the model can only see the right end of buffers between them. */
	template <typename Data>
	class Latch
	{
	public:
	typedef MinorBuffer<Data> Buffer;

	protected:
	/** Delays, in cycles, writing data into the latch and seeing it on the
	* latched wires */
	Cycles delay;

	Buffer buffer;

	public:
	/** forward/backwardDelay specify the delay from input to output in each
	* direction. These arguments must be >= 1 */
	Latch(const std::string &name,
	const std::string &data_name,
	Cycles delay_ = Cycles(1),
	bool report_backwards = false) :
	delay(delay_),
	buffer(name, data_name, delay_, 0, (report_backwards ? -delay_ : 0),
	(report_backwards ? 0 : -delay_))
	{ }

	public:
	/** Encapsulate wires on either input or output of the latch.
	* forward/backward correspond to data direction relative to the
	* pipeline. Latched and Immediate specify delay for backward data.
	* Immediate data is available to earlier stages during the cycle it
	* is written */
	class Input
	{
	public:
	typename Buffer::wire inputWire;

	public:
	Input(typename Buffer::wire input_wire) :
	inputWire(input_wire)
	{ }
	};

	class Output
	{
	public:
	typename Buffer::wire outputWire;

	public:
	Output(typename Buffer::wire output_wire) :
	outputWire(output_wire)
	{ }
	};

	bool empty() const { return buffer.empty(); }

	/** An interface to just the input of the buffer */
	Input input() { return Input(buffer.getWire(0)); }

	/** An interface to just the output of the buffer */
	Output output() { return Output(buffer.getWire(-delay)); }

	void minorTrace() const { buffer.minorTrace(); }

	void evaluate() { buffer.advance(); }
	};

	/** A pipeline simulating class that will stall (not advance when advance()
	* is called) if a non-bubble value lies at the far end of the pipeline.
	* The user can clear the stall before calling advance to unstall the
	* pipeline. */
	template <typename ElemType,
	typename ReportTraits,
	typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
	class SelfStallingPipeline : public MinorBuffer<ElemType, ReportTraits>
	{
	protected:
	/** Wire at the input end of the pipeline (for convenience) */
	typename TimeBuffer<ElemType>::wire pushWire;
	/** Wire at the output end of the pipeline (for convenience) */
	typename TimeBuffer<ElemType>::wire popWire;

	public:
	/** If true, advance will not advance the pipeline */
	bool stalled;

	/** The number of slots with non-bubbles in them */
	unsigned int occupancy;

	public:
	SelfStallingPipeline(const std::string &name,
	const std::string &data_name,
	unsigned depth) :
	MinorBuffer<ElemType, ReportTraits>
	(name, data_name, depth, 0, -1, -depth),
	pushWire(this->getWire(0)),
	popWire(this->getWire(-depth)),
	stalled(false),
	occupancy(0)
	{
	assert(depth > 0);

	/* Write explicit bubbles to get around the case where the default
	* constructor for the element type isn't good enough */
	for (unsigned i = 0; i <= depth; i++)
	(*this)[-i] = BubbleTraits::bubble();
	}

	public:
	/** Write an element to the back of the pipeline. This doesn't cause
	* the pipeline to advance until advance is called. Pushing twice
	* without advance-ing will just cause an overwrite of the last push's
	* data. */
	void push(ElemType &elem)
	{
	assert(!alreadyPushed());
	*pushWire = elem;
	if (!BubbleTraits::isBubble(elem))
	occupancy++;
	}

	/** Peek at the end element of the pipe */
	ElemType &front() { return *popWire; }

	const ElemType &front() const { return *popWire; }

	/** Have we already pushed onto this pipe without advancing */
	bool alreadyPushed() { return !BubbleTraits::isBubble(*pushWire); }

	/** There's data (not a bubble) at the end of the pipe */
	bool isPopable() { return !BubbleTraits::isBubble(front()); }

	/** Try to advance the pipeline. If we're stalled, don't advance. If
	* we're not stalled, advance then check to see if we become stalled
	* (a non-bubble at the end of the pipe) */
	void
	advance()
	{
	bool data_at_end = isPopable();

	if (!stalled) {
	TimeBuffer<ElemType>::advance();
	/* If there was data at the end of the pipe that has now been
	* advanced out of the pipe, we've lost data */
	if (data_at_end)
	occupancy--;
	/* Is there data at the end of the pipe now? */
	stalled = isPopable();
	/* Insert a bubble into the empty input slot to make sure that
	* element is correct in the case where the default constructor
	* for ElemType doesn't produce a bubble */
	ElemType bubble = BubbleTraits::bubble();
	*pushWire = bubble;
	}
	}
	};

	/** Base class for space reservation requestable objects */
	class Reservable
	{
	public:
	/** Can a slot be reserved? */
	virtual bool canReserve() const = 0;

	/** Reserve a slot in whatever structure this is attached to */
	virtual void reserve() = 0;

	/** Free a reserved slot */
	virtual void freeReservation() = 0;

	virtual ~Reservable() {};
	};

	/** Wrapper for a queue type to act as a pipeline stage input queue.
	* Handles capacity management, bubble value suppression and provides
	* reporting.
	*
	* In an ideal world, ElemType would be derived from ReportIF and BubbleIF,
	* but here we use traits and allow the Adaptors ReportTraitsAdaptor and
	* BubbleTraitsAdaptor to work on data which does directly implement
	* those interfaces. */
	template <typename ElemType,
	typename ReportTraits = ReportTraitsAdaptor<ElemType>,
	typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
	class Queue : public Named, public Reservable
	{
	private:
	std::deque<ElemType> queue;

	/** Number of slots currently reserved for future (reservation
	* respecting) pushes */
	unsigned int numReservedSlots;

	/** Need this here as queues usually don't have a limited capacity */
	unsigned int capacity;

	/** Name to use for the data in MinorTrace */
	std::string dataName;

	public:
	Queue(const std::string &name, const std::string &data_name,
	unsigned int capacity_) :
	Named(name),
	numReservedSlots(0),
	capacity(capacity_),
	dataName(data_name)
	{ }

	public:
	/** Push an element into the buffer if it isn't a bubble. Bubbles are
	* just discarded. It is assummed that any push into a queue with
	* reserved space intends to take that space */
	void
	push(ElemType &data)
	{
	if (!BubbleTraits::isBubble(data)) {
	freeReservation();
	queue.push_back(data);

	if (queue.size() > capacity) {
	warn("%s: No space to push data into queue of capacity"
	" %u, pushing anyway\n", name(), capacity);
	}

	}
	}

	/** Clear all allocated space. Be careful how this is used */
	void clearReservedSpace() { numReservedSlots = 0; }

	/** Clear a single reserved slot */
	void freeReservation()
	{
	if (numReservedSlots != 0)
	numReservedSlots--;
	}

	/** Reserve space in the queue for future pushes. Enquiries about space
	* in the queue using unreservedRemainingSpace will only tell about
	* space which is not full and not reserved. */
	void
	reserve()
	{
	/* Check reservable space */
	if (unreservedRemainingSpace() == 0)
	warn("%s: No space is reservable in queue", name());

	numReservedSlots++;
	}

	bool canReserve() const { return unreservedRemainingSpace() != 0; }

	/** Number of slots available in an empty buffer */
	unsigned int totalSpace() const { return capacity; }

	/** Number of slots already occupied in this buffer */
	unsigned int occupiedSpace() const { return queue.size(); }

	/** Number of slots which are reserved. */
	unsigned int reservedSpace() const { return numReservedSlots; }

	/** Number of slots yet to fill in this buffer. This doesn't include
	* reservation. */
	unsigned int
	remainingSpace() const
	{
	int ret = capacity - queue.size();

	return (ret < 0 ? 0 : ret);
	}

	/** Like remainingSpace but does not count reserved spaces */
	unsigned int
	unreservedRemainingSpace() const
	{
	int ret = capacity - (queue.size() + numReservedSlots);

	return (ret < 0 ? 0 : ret);
	}

	/** Head value. Like std::queue::front */
	ElemType &front() { return queue.front(); }

	const ElemType &front() const { return queue.front(); }

	/** Pop the head item. Like std::queue::pop */
	void pop() { queue.pop_front(); }

	/** Is the queue empty? */
	bool empty() const { return queue.empty(); }

	void
	minorTrace() const
	{
	std::ostringstream data;
	/* If we become over-full, totalSpace() can actually be smaller than
	* occupiedSpace(). Handle this */
	unsigned int num_total = (occupiedSpace() > totalSpace() ?
	occupiedSpace() : totalSpace());

	unsigned int num_reserved = reservedSpace();
	unsigned int num_occupied = occupiedSpace();

	int num_printed = 1;
	/* Bodge to rotate queue to report elements */
	while (num_printed <= num_occupied) {
	ReportTraits::reportData(data, queue[num_printed - 1]);
	num_printed++;

	if (num_printed <= num_total)
	data << ',';
	}

	int num_printed_reserved = 1;
	/* Show reserved slots */
	while (num_printed_reserved <= num_reserved &&
	num_printed <= num_total)
	{
	data << 'R';
	num_printed_reserved++;
	num_printed++;

	if (num_printed <= num_total)
	data << ',';
	}

	/* And finally pad with empty slots (if there are any) */
	while (num_printed <= num_total) {
	num_printed++;

	if (num_printed <= num_total)
	data << ',';
	}

	minor::minorTrace("%s=%s\n", dataName, data.str());
	}
	};

	/** Like a Queue but with a restricted interface and a setTail function
	* which, when the queue is empty, just takes a reference to the pushed
	* item as the single element. Calling pushTail will push that element
	* onto the queue.
	*
	* The purpose of this class is to allow the faster operation of queues of
	* items which usually don't get deeper than one item and for which the copy
	* associated with a push is expensive enough to want to avoid
	*
	* The intended use case is the input buffer for pipeline stages, hence the
	* class name */
	template <typename ElemType,
	typename ReportTraits = ReportTraitsAdaptor<ElemType>,
	typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
	class InputBuffer : public Reservable
	{
	protected:
	/** Underlying queue */
	mutable Queue<ElemType, ReportTraits, BubbleTraits> queue;

	/** Pointer to the single element (if not NULL) */
	mutable ElemType *elementPtr;

	public:
	InputBuffer(const std::string &name, const std::string &data_name,
	unsigned int capacity_) :
	queue(name, data_name, capacity_),
	elementPtr(NULL)
	{ }

	public:
	/** Set the tail of the queue, this is like push but needs
	* to be followed by pushTail for the new tail to make its
	* way into the queue proper */
	void
	setTail(ElemType &new_element)
	{
	assert(!elementPtr);
	if (!BubbleTraits::isBubble(new_element)) {
	if (queue.empty())
	elementPtr = &new_element;
	else
	queue.push(new_element);
	}
	}

	/** No single element or queue entries */
	bool empty() const { return !elementPtr && queue.empty(); }

	/** Return the element, or the front of the queue */
	const ElemType &front() const
	{ return (elementPtr ? *elementPtr : queue.front()); }

	ElemType &front()
	{ return (elementPtr ? *elementPtr : queue.front()); }

	/** Pop either the head, or if none, the head of the queue */
	void
	pop()
	{
	if (elementPtr) {
	/* A popped element was expected to be pushed into queue
	* and so take a reserved space */
	elementPtr = NULL;
	queue.freeReservation();
	} else {
	queue.pop();
	}
	}

	/** Push the single element (if any) into the queue proper. If the
	* element's reference points to a transient object, remember to
	* always do this before the end of that object's life */
	void
	pushTail() const
	{
	if (elementPtr)
	queue.push(*elementPtr);
	elementPtr = NULL;
	}

	/** Report elements */
	void
	minorTrace() const
	{
	pushTail();
	queue.minorTrace();
	}

	/** Reservable interface, passed on to queue */
	bool canReserve() const { return queue.canReserve(); }
	void reserve() { queue.reserve(); }
	void freeReservation() { queue.freeReservation(); }

	/** Like remainingSpace but does not count reserved spaces */
	unsigned int
	unreservedRemainingSpace()
	{
	pushTail();
	return queue.unreservedRemainingSpace();
	}
	};

	} // namespace minor
	} // namespace gem5

	#endif /* __CPU_MINOR_BUFFERS_HH__ */