src/mem/tport.hh

   1 /*
   2  * Copyright (c) 2006 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Ali Saidi
  29  */
  30
  31 #ifndef __MEM_TPORT_HH__
  32 #define __MEM_TPORT_HH__
  33
  34 /**
  35  * @file
  36  *
  37  * Declaration of SimpleTimingPort.
  38  */
  39
  40 #include "mem/port.hh"
  41 #include "sim/eventq.hh"
  42 #include <list>
  43 #include <string>
  44
  45 /**
  46  * A simple port for interfacing objects that basically have only
  47  * functional memory behavior (e.g. I/O devices) to the memory system.
  48  * Both timing and functional accesses are implemented in terms of
  49  * atomic accesses.  A derived port class thus only needs to provide
  50  * recvAtomic() to support all memory access modes.
  51  *
  52  * The tricky part is handling recvTiming(), where the response must
  53  * be scheduled separately via a later call to sendTiming().  This
  54  * feature is handled by scheduling an internal event that calls
  55  * sendTiming() after a delay, and optionally rescheduling the
  56  * response if it is nacked.
  57  */
  58 class SimpleTimingPort : public Port
  59 {
  60   protected:
  61     /** A deferred packet, buffered to transmit later. */
  62     class DeferredPacket {
  63       public:
  64         Tick tick;      ///< The tick when the packet is ready to transmit
  65         PacketPtr pkt;  ///< Pointer to the packet to transmit
  66         DeferredPacket(Tick t, PacketPtr p)
  67             : tick(t), pkt(p)
  68         {}
  69     };
  70
  71     typedef std::list<DeferredPacket> DeferredPacketList;
  72     typedef std::list<DeferredPacket>::iterator DeferredPacketIterator;
  73
  74     /** A list of outgoing timing response packets that haven't been
  75      * serviced yet. */
  76     DeferredPacketList transmitList;
  77
  78     /** This function attempts to send deferred packets.  Scheduled to
  79      * be called in the future via SendEvent. */
  80     void processSendEvent();
  81
  82     /**
  83      * This class is used to implemented sendTiming() with a delay. When
  84      * a delay is requested a the event is scheduled if it isn't already.
  85      * When the event time expires it attempts to send the packet.
  86      * If it cannot, the packet sent when recvRetry() is called.
  87      **/
  88     typedef EventWrapper<SimpleTimingPort, &SimpleTimingPort::processSendEvent>
  89             SendEvent;
  90
  91     Event *sendEvent;
  92
  93     /** If we need to drain, keep the drain event around until we're done
  94      * here.*/
  95     Event *drainEvent;
  96
  97     /** Remember whether we're awaiting a retry from the bus. */
  98     bool waitingOnRetry;
  99
 100     /** Check the list of buffered packets against the supplied
 101      * functional request. */
 102     void checkFunctional(PacketPtr funcPkt);
 103
 104     /** Check whether we have a packet ready to go on the transmit list. */
 105     bool deferredPacketReady()
 106     { return !transmitList.empty() && transmitList.front().tick <= curTick; }
 107
 108     /** Schedule a sendTiming() event to be called in the future.
 109      * @param pkt packet to send
 110      * @param absolute time (in ticks) to send packet
 111      */
 112     void schedSendTiming(PacketPtr pkt, Tick when);
 113
 114     /** Attempt to send the packet at the head of the deferred packet
 115      * list.  Caller must guarantee that the deferred packet list is
 116      * non-empty and that the head packet is scheduled for curTick (or
 117      * earlier).
 118      */
 119     void sendDeferredPacket();
 120
 121     /** This function is notification that the device should attempt to send a
 122      * packet again. */
 123     virtual void recvRetry();
 124
 125     /** Implemented using recvAtomic(). */
 126     void recvFunctional(PacketPtr pkt);
 127
 128     /** Implemented using recvAtomic(). */
 129     bool recvTiming(PacketPtr pkt);
 130
 131     /**
 132      * Simple ports generally don't care about any status
 133      * changes... can always override this in cases where that's not
 134      * true. */
 135     virtual void recvStatusChange(Status status) { }
 136
 137
 138   public:
 139
 140     SimpleTimingPort(std::string pname, MemObject *_owner = NULL)
 141         : Port(pname, _owner),
 142           sendEvent(new SendEvent(this)),
 143           drainEvent(NULL),
 144           waitingOnRetry(false)
 145     {}
 146
 147     ~SimpleTimingPort() { delete sendEvent; }
 148
 149     /** Hook for draining timing accesses from the system.  The
 150      * associated SimObject's drain() functions should be implemented
 151      * something like this when this class is used:
 152      \code
 153           PioDevice::drain(Event *de)
 154           {
 155               unsigned int count;
 156               count = SimpleTimingPort->drain(de);
 157               if (count)
 158                   changeState(Draining);
 159               else
 160                   changeState(Drained);
 161               return count;
 162           }
 163      \endcode
 164     */
 165     unsigned int drain(Event *de);
 166 };
 167
 168 #endif // __MEM_TPORT_HH__