gem5/src/mem/coherent_bus.hh

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 * All rights reserved.
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 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
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 * this software without specific prior written permission.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 *
 * Authors: Ron Dreslinski
 *          Ali Saidi
 *          Andreas Hansson
 *          William Wang
 */

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

#ifndef __MEM_COHERENT_BUS_HH__
#define __MEM_COHERENT_BUS_HH__

#include "base/hashmap.hh"
#include "mem/bus.hh"
#include "params/CoherentBus.hh"

/**
 * A coherent bus 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 bus 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 CoherentBus : public BaseBus
{

  protected:

    /**
     * Declare the layers of this bus, 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 bus slave port type, one will be
     * instantiated for each of the master ports connecting to the
     * bus.
     */
    class CoherentBusSlavePort : public SlavePort
    {

      private:

        /** A reference to the bus to which this port belongs. */
        CoherentBus &bus;

      public:

        CoherentBusSlavePort(const std::string &_name,
                             CoherentBus &_bus, PortID _id)
            : SlavePort(_name, &_bus, _id), bus(_bus)
        { }

      protected:

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

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

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

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

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

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

    };

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

      public:

        CoherentBusMasterPort(const std::string &_name,
                              CoherentBus &_bus, PortID _id)
            : MasterPort(_name, &_bus, _id), bus(_bus)
        { }

      protected:

        /**
         * Determine if this port should be considered a snooper. For
         * a coherent bus 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 bus.
         */
        virtual bool recvTimingResp(PacketPtr pkt)
        { return bus.recvTimingResp(pkt, id); }

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

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

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

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

        /** When reciving a retry from the peer port (at id),
            pass it to the bus. */
        virtual void recvRetry()
        { bus.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, CoherentBus& _bus) :
            MasterPort(slave_port.name() + ".snoopRespPort", &_bus),
            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 bus 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;

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

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

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

    /** Function called by the port when the bus is recieving a timing
        snoop response.*/
    virtual 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);

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

    /** Function called by the port when the bus 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);

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

    /** Function called by the port when the bus 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 dataThroughBus;
    Stats::Scalar snoopDataThroughBus;

  public:

    virtual void init();

    CoherentBus(const CoherentBusParams *p);

    virtual ~CoherentBus();

    unsigned int drain(DrainManager *dm);

    virtual void regStats();
};

#endif //__MEM_COHERENT_BUS_HH__