src/mem/coherent_xbar.hh - arm/gem5 - Git at Google

 /*
  * Copyright (c) 2011-2014 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
  * not be construed as granting a license to any other intellectual
  * property including but not limited to intellectual property relating
  * to a hardware implementation of the functionality of the software
  * licensed hereunder.  You may use the software subject to the license
  * terms below provided that you ensure that this notice is replicated
  * unmodified and in its entirety in all distributions of the software,
  * modified or unmodified, in source code or in binary form.
  *
  * Copyright (c) 2002-2005 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.
  *
  * Authors: Ron Dreslinski
  *          Ali Saidi
  *          Andreas Hansson
  *          William Wang
  */

 /**
  * @file
  * Declaration of a coherent crossbar.
  */

 #ifndef __MEM_COHERENT_XBAR_HH__
 #define __MEM_COHERENT_XBAR_HH__

 #include "base/hashmap.hh"
 #include "mem/snoop_filter.hh"
 #include "mem/xbar.hh"
 #include "params/CoherentXBar.hh"

 /**
  * A coherent crossbar connects a number of (potentially) snooping
  * masters and slaves, and routes the request and response packets
  * based on the address, and also forwards all requests to the
  * snoopers and deals with the snoop responses.
  *
  * The coherent crossbar can be used as a template for modelling QPI,
  * HyperTransport, ACE and coherent OCP buses, and is typically used
  * for the L1-to-L2 buses and as the main system interconnect.  @sa
  * \ref gem5MemorySystem "gem5 Memory System"
  */
 class CoherentXBar : public BaseXBar
 {

   protected:

     /**
      * Declare the layers of this crossbar, one vector for requests,
      * one for responses, and one for snoop responses
      */
     typedef Layer<SlavePort,MasterPort> ReqLayer;
     typedef Layer<MasterPort,SlavePort> RespLayer;
     typedef Layer<SlavePort,MasterPort> SnoopLayer;
     std::vector<ReqLayer*> reqLayers;
     std::vector<RespLayer*> respLayers;
     std::vector<SnoopLayer*> snoopLayers;

     /**
      * Declaration of the coherent crossbar slave port type, one will
      * be instantiated for each of the master ports connecting to the
      * crossbar.
      */
     class CoherentXBarSlavePort : public SlavePort
     {

       private:

         /** A reference to the crossbar to which this port belongs. */
         CoherentXBar &xbar;

       public:

         CoherentXBarSlavePort(const std::string &_name,
                              CoherentXBar &_xbar, PortID _id)
             : SlavePort(_name, &_xbar, _id), xbar(_xbar)
         { }

       protected:

         /**
          * When receiving a timing request, pass it to the crossbar.
          */
         virtual bool recvTimingReq(PacketPtr pkt)
         { return xbar.recvTimingReq(pkt, id); }

         /**
          * When receiving a timing snoop response, pass it to the crossbar.
          */
         virtual bool recvTimingSnoopResp(PacketPtr pkt)
         { return xbar.recvTimingSnoopResp(pkt, id); }

         /**
          * When receiving an atomic request, pass it to the crossbar.
          */
         virtual Tick recvAtomic(PacketPtr pkt)
         { return xbar.recvAtomic(pkt, id); }

         /**
          * When receiving a functional request, pass it to the crossbar.
          */
         virtual void recvFunctional(PacketPtr pkt)
         { xbar.recvFunctional(pkt, id); }

         /**
          * When receiving a retry, pass it to the crossbar.
          */
         virtual void recvRetry()
         { panic("Crossbar slave ports should never retry.\n"); }

         /**
          * Return the union of all adress ranges seen by this crossbar.
          */
         virtual AddrRangeList getAddrRanges() const
         { return xbar.getAddrRanges(); }

     };

     /**
      * Declaration of the coherent crossbar master port type, one will be
      * instantiated for each of the slave interfaces connecting to the
      * crossbar.
      */
     class CoherentXBarMasterPort : public MasterPort
     {
       private:
         /** A reference to the crossbar to which this port belongs. */
         CoherentXBar &xbar;

       public:

         CoherentXBarMasterPort(const std::string &_name,
                               CoherentXBar &_xbar, PortID _id)
             : MasterPort(_name, &_xbar, _id), xbar(_xbar)
         { }

       protected:

         /**
          * Determine if this port should be considered a snooper. For
          * a coherent crossbar master port this is always true.
          *
          * @return a boolean that is true if this port is snooping
          */
         virtual bool isSnooping() const
         { return true; }

         /**
          * When receiving a timing response, pass it to the crossbar.
          */
         virtual bool recvTimingResp(PacketPtr pkt)
         { return xbar.recvTimingResp(pkt, id); }

         /**
          * When receiving a timing snoop request, pass it to the crossbar.
          */
         virtual void recvTimingSnoopReq(PacketPtr pkt)
         { return xbar.recvTimingSnoopReq(pkt, id); }

         /**
          * When receiving an atomic snoop request, pass it to the crossbar.
          */
         virtual Tick recvAtomicSnoop(PacketPtr pkt)
         { return xbar.recvAtomicSnoop(pkt, id); }

         /**
          * When receiving a functional snoop request, pass it to the crossbar.
          */
         virtual void recvFunctionalSnoop(PacketPtr pkt)
         { xbar.recvFunctionalSnoop(pkt, id); }

         /** When reciving a range change from the peer port (at id),
             pass it to the crossbar. */
         virtual void recvRangeChange()
         { xbar.recvRangeChange(id); }

         /** When reciving a retry from the peer port (at id),
             pass it to the crossbar. */
         virtual void recvRetry()
         { xbar.recvRetry(id); }

     };

     /**
      * Internal class to bridge between an incoming snoop response
      * from a slave port and forwarding it through an outgoing slave
      * port. It is effectively a dangling master port.
      */
     class SnoopRespPort : public MasterPort
     {

       private:

         /** The port which we mirror internally. */
         SlavePort& slavePort;

       public:

         /**
          * Create a snoop response port that mirrors a given slave port.
          */
         SnoopRespPort(SlavePort& slave_port, CoherentXBar& _xbar) :
             MasterPort(slave_port.name() + ".snoopRespPort", &_xbar),
             slavePort(slave_port) { }

         /**
          * Override the sending of retries and pass them on through
          * the mirrored slave port.
          */
         void sendRetry() {
             slavePort.sendRetry();
         }

         /**
          * Provided as necessary.
          */
         void recvRetry() { panic("SnoopRespPort should never see retry\n"); }

         /**
          * Provided as necessary.
          */
         bool recvTimingResp(PacketPtr pkt)
         {
             panic("SnoopRespPort should never see timing response\n");
             return false;
         }

     };

     std::vector<SnoopRespPort*> snoopRespPorts;

     std::vector<SlavePort*> snoopPorts;

     /**
      * Store the outstanding requests so we can determine which ones
      * we generated and which ones were merely forwarded. This is used
      * in the coherent crossbar when coherency responses come back.
      */
     m5::hash_set<RequestPtr> outstandingReq;

     /**
      * Keep a pointer to the system to be allow to querying memory system
      * properties.
      */
     System *system;

     /** A snoop filter that tracks cache line residency and can restrict the
       * broadcast needed for probes.  NULL denotes an absent filter. */
     SnoopFilter *snoopFilter;

     /** Function called by the port when the crossbar is recieving a Timing
       request packet.*/
     bool recvTimingReq(PacketPtr pkt, PortID slave_port_id);

     /** Function called by the port when the crossbar is recieving a Timing
       response packet.*/
     bool recvTimingResp(PacketPtr pkt, PortID master_port_id);

     /** Function called by the port when the crossbar is recieving a timing
         snoop request.*/
     void recvTimingSnoopReq(PacketPtr pkt, PortID master_port_id);

     /** Function called by the port when the crossbar is recieving a timing
         snoop response.*/
     bool recvTimingSnoopResp(PacketPtr pkt, PortID slave_port_id);

     /** Timing function called by port when it is once again able to process
      * requests. */
     void recvRetry(PortID master_port_id);

     /**
      * Forward a timing packet to our snoopers, potentially excluding
      * one of the connected coherent masters to avoid sending a packet
      * back to where it came from.
      *
      * @param pkt Packet to forward
      * @param exclude_slave_port_id Id of slave port to exclude
      */
     void forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id) {
         forwardTiming(pkt, exclude_slave_port_id, snoopPorts);
     }

     /**
      * Forward a timing packet to a selected list of snoopers, potentially
      * excluding one of the connected coherent masters to avoid sending a packet
      * back to where it came from.
      *
      * @param pkt Packet to forward
      * @param exclude_slave_port_id Id of slave port to exclude
      * @param dests Vector of destination ports for the forwarded pkt
      */
     void forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id,
                        const std::vector<SlavePort*>& dests);

     /** Function called by the port when the crossbar is recieving a Atomic
       transaction.*/
     Tick recvAtomic(PacketPtr pkt, PortID slave_port_id);

     /** Function called by the port when the crossbar is recieving an
         atomic snoop transaction.*/
     Tick recvAtomicSnoop(PacketPtr pkt, PortID master_port_id);

     /**
      * Forward an atomic packet to our snoopers, potentially excluding
      * one of the connected coherent masters to avoid sending a packet
      * back to where it came from.
      *
      * @param pkt Packet to forward
      * @param exclude_slave_port_id Id of slave port to exclude
      *
      * @return a pair containing the snoop response and snoop latency
      */
     std::pair<MemCmd, Tick> forwardAtomic(PacketPtr pkt,
                                           PortID exclude_slave_port_id)
     {
         return forwardAtomic(pkt, exclude_slave_port_id, InvalidPortID, snoopPorts);
     }

     /**
      * Forward an atomic packet to a selected list of snoopers, potentially
      * excluding one of the connected coherent masters to avoid sending a packet
      * back to where it came from.
      *
      * @param pkt Packet to forward
      * @param exclude_slave_port_id Id of slave port to exclude
      * @param source_master_port_id Id of the master port for snoops from below
      * @param dests Vector of destination ports for the forwarded pkt
      *
      * @return a pair containing the snoop response and snoop latency
      */
     std::pair<MemCmd, Tick> forwardAtomic(PacketPtr pkt,
                                           PortID exclude_slave_port_id,
                                           PortID source_master_port_id,
                                           const std::vector<SlavePort*>& dests);

     /** Function called by the port when the crossbar is recieving a Functional
         transaction.*/
     void recvFunctional(PacketPtr pkt, PortID slave_port_id);

     /** Function called by the port when the crossbar is recieving a functional
         snoop transaction.*/
     void recvFunctionalSnoop(PacketPtr pkt, PortID master_port_id);

     /**
      * Forward a functional packet to our snoopers, potentially
      * excluding one of the connected coherent masters to avoid
      * sending a packet back to where it came from.
      *
      * @param pkt Packet to forward
      * @param exclude_slave_port_id Id of slave port to exclude
      */
     void forwardFunctional(PacketPtr pkt, PortID exclude_slave_port_id);

     Stats::Scalar snoops;
     Stats::Distribution snoopFanout;

   public:

     virtual void init();

     CoherentXBar(const CoherentXBarParams *p);

     virtual ~CoherentXBar();

     unsigned int drain(DrainManager *dm);

     virtual void regStats();
 };

 #endif //__MEM_COHERENT_XBAR_HH__
	/*
	* Copyright (c) 2011-2014 ARM Limited
	* All rights reserved
	*
	* The license below extends only to copyright in the software and shall
	* not be construed as granting a license to any other intellectual
	* property including but not limited to intellectual property relating
	* to a hardware implementation of the functionality of the software
	* licensed hereunder. You may use the software subject to the license
	* terms below provided that you ensure that this notice is replicated
	* unmodified and in its entirety in all distributions of the software,
	* modified or unmodified, in source code or in binary form.
	*
	* Copyright (c) 2002-2005 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.
	*
	* Authors: Ron Dreslinski
	* Ali Saidi
	* Andreas Hansson
	* William Wang
	*/

	/**
	* @file
	* Declaration of a coherent crossbar.
	*/

	#ifndef __MEM_COHERENT_XBAR_HH__
	#define __MEM_COHERENT_XBAR_HH__

	#include "base/hashmap.hh"
	#include "mem/snoop_filter.hh"
	#include "mem/xbar.hh"
	#include "params/CoherentXBar.hh"

	/**
	* A coherent crossbar connects a number of (potentially) snooping
	* masters and slaves, and routes the request and response packets
	* based on the address, and also forwards all requests to the
	* snoopers and deals with the snoop responses.
	*
	* The coherent crossbar can be used as a template for modelling QPI,
	* HyperTransport, ACE and coherent OCP buses, and is typically used
	* for the L1-to-L2 buses and as the main system interconnect. @sa
	* \ref gem5MemorySystem "gem5 Memory System"
	*/
	class CoherentXBar : public BaseXBar
	{

	protected:

	/**
	* Declare the layers of this crossbar, one vector for requests,
	* one for responses, and one for snoop responses
	*/
	typedef Layer<SlavePort,MasterPort> ReqLayer;
	typedef Layer<MasterPort,SlavePort> RespLayer;
	typedef Layer<SlavePort,MasterPort> SnoopLayer;
	std::vector<ReqLayer*> reqLayers;
	std::vector<RespLayer*> respLayers;
	std::vector<SnoopLayer*> snoopLayers;

	/**
	* Declaration of the coherent crossbar slave port type, one will
	* be instantiated for each of the master ports connecting to the
	* crossbar.
	*/
	class CoherentXBarSlavePort : public SlavePort
	{

	private:

	/** A reference to the crossbar to which this port belongs. */
	CoherentXBar &xbar;

	public:

	CoherentXBarSlavePort(const std::string &_name,
	CoherentXBar &_xbar, PortID _id)
	: SlavePort(_name, &_xbar, _id), xbar(_xbar)
	{ }

	protected:

	/**
	* When receiving a timing request, pass it to the crossbar.
	*/
	virtual bool recvTimingReq(PacketPtr pkt)
	{ return xbar.recvTimingReq(pkt, id); }

	/**
	* When receiving a timing snoop response, pass it to the crossbar.
	*/
	virtual bool recvTimingSnoopResp(PacketPtr pkt)
	{ return xbar.recvTimingSnoopResp(pkt, id); }

	/**
	* When receiving an atomic request, pass it to the crossbar.
	*/
	virtual Tick recvAtomic(PacketPtr pkt)
	{ return xbar.recvAtomic(pkt, id); }

	/**
	* When receiving a functional request, pass it to the crossbar.
	*/
	virtual void recvFunctional(PacketPtr pkt)
	{ xbar.recvFunctional(pkt, id); }

	/**
	* When receiving a retry, pass it to the crossbar.
	*/
	virtual void recvRetry()
	{ panic("Crossbar slave ports should never retry.\n"); }

	/**
	* Return the union of all adress ranges seen by this crossbar.
	*/
	virtual AddrRangeList getAddrRanges() const
	{ return xbar.getAddrRanges(); }

	};

	/**
	* Declaration of the coherent crossbar master port type, one will be
	* instantiated for each of the slave interfaces connecting to the
	* crossbar.
	*/
	class CoherentXBarMasterPort : public MasterPort
	{
	private:
	/** A reference to the crossbar to which this port belongs. */
	CoherentXBar &xbar;

	public:

	CoherentXBarMasterPort(const std::string &_name,
	CoherentXBar &_xbar, PortID _id)
	: MasterPort(_name, &_xbar, _id), xbar(_xbar)
	{ }

	protected:

	/**
	* Determine if this port should be considered a snooper. For
	* a coherent crossbar master port this is always true.
	*
	* @return a boolean that is true if this port is snooping
	*/
	virtual bool isSnooping() const
	{ return true; }

	/**
	* When receiving a timing response, pass it to the crossbar.
	*/
	virtual bool recvTimingResp(PacketPtr pkt)
	{ return xbar.recvTimingResp(pkt, id); }

	/**
	* When receiving a timing snoop request, pass it to the crossbar.
	*/
	virtual void recvTimingSnoopReq(PacketPtr pkt)
	{ return xbar.recvTimingSnoopReq(pkt, id); }

	/**
	* When receiving an atomic snoop request, pass it to the crossbar.
	*/
	virtual Tick recvAtomicSnoop(PacketPtr pkt)
	{ return xbar.recvAtomicSnoop(pkt, id); }

	/**
	* When receiving a functional snoop request, pass it to the crossbar.
	*/
	virtual void recvFunctionalSnoop(PacketPtr pkt)
	{ xbar.recvFunctionalSnoop(pkt, id); }

	/** When reciving a range change from the peer port (at id),
	pass it to the crossbar. */
	virtual void recvRangeChange()
	{ xbar.recvRangeChange(id); }

	/** When reciving a retry from the peer port (at id),
	pass it to the crossbar. */
	virtual void recvRetry()
	{ xbar.recvRetry(id); }

	};

	/**
	* Internal class to bridge between an incoming snoop response
	* from a slave port and forwarding it through an outgoing slave
	* port. It is effectively a dangling master port.
	*/
	class SnoopRespPort : public MasterPort
	{

	private:

	/** The port which we mirror internally. */
	SlavePort& slavePort;

	public:

	/**
	* Create a snoop response port that mirrors a given slave port.
	*/
	SnoopRespPort(SlavePort& slave_port, CoherentXBar& _xbar) :
	MasterPort(slave_port.name() + ".snoopRespPort", &_xbar),
	slavePort(slave_port) { }

	/**
	* Override the sending of retries and pass them on through
	* the mirrored slave port.
	*/
	void sendRetry() {
	slavePort.sendRetry();
	}

	/**
	* Provided as necessary.
	*/
	void recvRetry() { panic("SnoopRespPort should never see retry\n"); }

	/**
	* Provided as necessary.
	*/
	bool recvTimingResp(PacketPtr pkt)
	{
	panic("SnoopRespPort should never see timing response\n");
	return false;
	}

	};

	std::vector<SnoopRespPort*> snoopRespPorts;

	std::vector<SlavePort*> snoopPorts;

	/**
	* Store the outstanding requests so we can determine which ones
	* we generated and which ones were merely forwarded. This is used
	* in the coherent crossbar when coherency responses come back.
	*/
	m5::hash_set<RequestPtr> outstandingReq;

	/**
	* Keep a pointer to the system to be allow to querying memory system
	* properties.
	*/
	System *system;

	/** A snoop filter that tracks cache line residency and can restrict the
	* broadcast needed for probes. NULL denotes an absent filter. */
	SnoopFilter *snoopFilter;

	/** Function called by the port when the crossbar is recieving a Timing
	request packet.*/
	bool recvTimingReq(PacketPtr pkt, PortID slave_port_id);

	/** Function called by the port when the crossbar is recieving a Timing
	response packet.*/
	bool recvTimingResp(PacketPtr pkt, PortID master_port_id);

	/** Function called by the port when the crossbar is recieving a timing
	snoop request.*/
	void recvTimingSnoopReq(PacketPtr pkt, PortID master_port_id);

	/** Function called by the port when the crossbar is recieving a timing
	snoop response.*/
	bool recvTimingSnoopResp(PacketPtr pkt, PortID slave_port_id);

	/** Timing function called by port when it is once again able to process
	* requests. */
	void recvRetry(PortID master_port_id);

	/**
	* Forward a timing packet to our snoopers, potentially excluding
	* one of the connected coherent masters to avoid sending a packet
	* back to where it came from.
	*
	* @param pkt Packet to forward
	* @param exclude_slave_port_id Id of slave port to exclude
	*/
	void forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id) {
	forwardTiming(pkt, exclude_slave_port_id, snoopPorts);
	}

	/**
	* Forward a timing packet to a selected list of snoopers, potentially
	* excluding one of the connected coherent masters to avoid sending a packet
	* back to where it came from.
	*
	* @param pkt Packet to forward
	* @param exclude_slave_port_id Id of slave port to exclude
	* @param dests Vector of destination ports for the forwarded pkt
	*/
	void forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id,
	const std::vector<SlavePort*>& dests);

	/** Function called by the port when the crossbar is recieving a Atomic
	transaction.*/
	Tick recvAtomic(PacketPtr pkt, PortID slave_port_id);

	/** Function called by the port when the crossbar is recieving an
	atomic snoop transaction.*/
	Tick recvAtomicSnoop(PacketPtr pkt, PortID master_port_id);

	/**
	* Forward an atomic packet to our snoopers, potentially excluding
	* one of the connected coherent masters to avoid sending a packet
	* back to where it came from.
	*
	* @param pkt Packet to forward
	* @param exclude_slave_port_id Id of slave port to exclude
	*
	* @return a pair containing the snoop response and snoop latency
	*/
	std::pair<MemCmd, Tick> forwardAtomic(PacketPtr pkt,
	PortID exclude_slave_port_id)
	{
	return forwardAtomic(pkt, exclude_slave_port_id, InvalidPortID, snoopPorts);
	}

	/**
	* Forward an atomic packet to a selected list of snoopers, potentially
	* excluding one of the connected coherent masters to avoid sending a packet
	* back to where it came from.
	*
	* @param pkt Packet to forward
	* @param exclude_slave_port_id Id of slave port to exclude
	* @param source_master_port_id Id of the master port for snoops from below
	* @param dests Vector of destination ports for the forwarded pkt
	*
	* @return a pair containing the snoop response and snoop latency
	*/
	std::pair<MemCmd, Tick> forwardAtomic(PacketPtr pkt,
	PortID exclude_slave_port_id,
	PortID source_master_port_id,
	const std::vector<SlavePort*>& dests);

	/** Function called by the port when the crossbar is recieving a Functional
	transaction.*/
	void recvFunctional(PacketPtr pkt, PortID slave_port_id);

	/** Function called by the port when the crossbar is recieving a functional
	snoop transaction.*/
	void recvFunctionalSnoop(PacketPtr pkt, PortID master_port_id);

	/**
	* Forward a functional packet to our snoopers, potentially
	* excluding one of the connected coherent masters to avoid
	* sending a packet back to where it came from.
	*
	* @param pkt Packet to forward
	* @param exclude_slave_port_id Id of slave port to exclude
	*/
	void forwardFunctional(PacketPtr pkt, PortID exclude_slave_port_id);

	Stats::Scalar snoops;
	Stats::Distribution snoopFanout;

	public:

	virtual void init();

	CoherentXBar(const CoherentXBarParams *p);

	virtual ~CoherentXBar();

	unsigned int drain(DrainManager *dm);

	virtual void regStats();
	};

	#endif //__MEM_COHERENT_XBAR_HH__