MEM: Introduce the master/slave port sub-classes in C++

This patch introduces the notion of a master and slave port in the C++
code, thus bringing the previous classification from the Python
classes into the corresponding simulation objects and memory objects.

The patch enables us to classify behaviours into the two bins and add
assumptions and enfore compliance, also simplifying the two
interfaces. As a starting point, isSnooping is confined to a master
port, and getAddrRanges to slave ports. More of these specilisations
are to come in later patches.

The getPort function is not getMasterPort and getSlavePort, and
returns a port reference rather than a pointer as NULL would never be
a valid return value. The default implementation of these two
functions is placed in MemObject, and calls fatal.

The one drawback with this specific patch is that it requires some
code duplication, e.g. QueuedPort becomes QueuedMasterPort and
QueuedSlavePort, and BusPort becomes BusMasterPort and BusSlavePort
(avoiding multiple inheritance). With the later introduction of the
port interfaces, moving the functionality outside the port itself, a
lot of the duplicated code will disappear again.

1 files changed, 159 insertions, 108 deletions

diff --git a/src/mem/port.hh b/src/mem/port.hh
index fef0c839d..80bb3b085 100644
--- a/src/mem/port.hh
+++ b/src/mem/port.hh
@@ -39,15 +39,12 @@
  *
  * Authors: Ron Dreslinski
  *          Andreas Hansson
+ *          William Wang
  */
 
 /**
  * @file
- * Port Object Declaration. Ports are used to interface memory objects to
- * each other.  They will always come in pairs, and we refer to the other
- * port object as the peer.  These are used to make the design more
- * modular so that a specific interface between every type of objcet doesn't
- * have to be created.
+ * Port Object Declaration.
  */
 
 #ifndef __MEM_PORT_HH__
@@ -58,7 +55,8 @@
 #include "base/range.hh"
 #include "mem/packet.hh"
 
-/** This typedef is used to clean up getAddrRanges(). It's declared
+/**
+ * This typedef is used to clean up getAddrRanges(). It's declared
  * outside the Port object since it's also used by some mem objects.
  * Eventually we should move this typedef to wherever Addr is
  * defined.
@@ -70,62 +68,47 @@ typedef std::list<Range<Addr> >::iterator AddrRangeIter;
 class MemObject;
 
 /**
- * Ports are used to interface memory objects to
- * each other.  They will always come in pairs, and we refer to the other
- * port object as the peer.  These are used to make the design more
- * modular so that a specific interface between every type of objcet doesn't
- * have to be created.
+ * Ports are used to interface memory objects to each other. A port is
+ * either a master or a slave and the connected peer is always of the
+ * opposite role.
  *
- * Recv accesor functions are being called from the peer interface.
- * Send accessor functions are being called from the device the port is
- * associated with, and it will call the peer recv. accessor function.
+ * Each port has a name and an owner, and enables three basic types of
+ * accesses to the peer port: sendFunctional, sendAtomic and
+ * sendTiming.
  */
 class Port
 {
-  protected:
+
+  private:
+
     /** Descriptive name (for DPRINTF output) */
-    mutable std::string portName;
+    std::string portName;
 
-    /** A pointer to the peer port.  Ports always come in pairs, that way they
-        can use a standardized interface to communicate between different
-        memory objects. */
-    Port *peer;
+  protected:
 
-    /** A pointer to the MemObject that owns this port. This may not be set. */
-    MemObject *owner;
+    /** A pointer to the peer port.  */
+    Port* peer;
+
+    /** A reference to the MemObject that owns this port. */
+    MemObject& owner;
 
-  public:
     /**
-     * Constructor.
+     * Abstract base class for ports
      *
-     * @param _name Port name for DPRINTF output.  Should include name
-     * of memory system object to which the port belongs.
-     * @param _owner Pointer to the MemObject that owns this port.
-     * Will not necessarily be set.
+     * @param _name Port name including the owners name
+     * @param _owner The MemObject that is the structural owner of this port
      */
-    Port(const std::string &_name, MemObject *_owner);
-
-    /** Return port name (for DPRINTF). */
-    const std::string &name() const { return portName; }
+    Port(const std::string& _name, MemObject& _owner);
 
+    /**
+     * Virtual destructor due to inheritance.
+     */
     virtual ~Port();
 
-    void setName(const std::string &name)
-    { portName = name; }
-
-    /** Function to set the pointer for the peer port. */
-    virtual void setPeer(Port *port);
-
-    /** Function to get the pointer to the peer port. */
-    Port *getPeer() { return peer; }
-
-    /** Function to set the owner of this port. */
-    void setOwner(MemObject *_owner);
-
-    /** Function to return the owner of this port. */
-    MemObject *getOwner() { return owner; }
+  public:
 
-    bool isConnected() { return peer != NULL; }
+    /** Return port name (for DPRINTF). */
+    const std::string name() const { return portName; }
 
   protected:
 
@@ -141,89 +124,109 @@ class Port
     /** Called to recive a functional call from the peer port. */
     virtual void recvFunctional(PacketPtr pkt) = 0;
 
-    /** Called to recieve an address range change from the peer port. */
-    virtual void recvRangeChange() = 0;
+    /**
+     * Called by a peer port if sendTiming was unsuccesful, and had to
+     * wait.
+     */
+    virtual void recvRetry() = 0;
 
-    /** Called by a peer port if the send was unsuccesful, and had to
-        wait.  This shouldn't be valid for response paths (IO Devices).
-        so it is set to panic if it isn't already defined.
-    */
-    virtual void recvRetry() { panic("??"); }
+  public:
 
-    /** Called by a peer port in order to determine the block size of the
-        device connected to this port.  It sometimes doesn't make sense for
-        this function to be called, so it just returns 0. Anytthing that is
-        concerned with the size should just ignore that.
+    /**
+     * Attempt to send a timing packet to the peer port by calling its
+     * receive function. If the send does not succeed, as indicated by
+     * the return value, then the sender must wait for a recvRetry at
+     * which point it can re-issue a sendTiming.
+     *
+     * @param pkt Packet to send.
+     *
+     * @return If the send was succesful or not.
     */
-    virtual unsigned deviceBlockSize() const { return 0; }
+    bool sendTiming(PacketPtr pkt) { return peer->recvTiming(pkt); }
 
-  public:
+    /**
+     * Send a retry to a peer port that previously attempted a sendTiming
+     * which was unsuccessful.
+     */
+    void sendRetry() { return peer->recvRetry(); }
 
     /**
-     * Get a list of the non-overlapping address ranges we are
-     * responsible for. The default implementation returns an empty
-     * list and thus no address ranges. Any slave port must override
-     * this function and return a populated list with at least one
-     * item.
+     * Send an atomic packet, where the data is moved and the state
+     * is updated in zero time, without interleaving with other
+     * memory accesses.
      *
-     * @return a list of ranges responded to
+     * @param pkt Packet to send.
+     *
+     * @return Estimated latency of access.
      */
-    virtual AddrRangeList getAddrRanges()
-    { AddrRangeList ranges; return ranges; }
+    Tick sendAtomic(PacketPtr pkt) { return peer->recvAtomic(pkt); }
 
     /**
-     * Determine if this port is snooping or not. The default
-     * implementation returns false and thus tells the neighbour we
-     * are not snooping. Any port that is to snoop (e.g. a cache
-     * connected to a bus) has to override this function.
+     * Send a functional packet, where the data is instantly updated
+     * everywhere in the memory system, without affecting the current
+     * state of any block or moving the block.
      *
-     * @return true if the port should be considered a snooper
+     * @param pkt Packet to send.
      */
-    virtual bool isSnooping()
-    { return false; }
-
-    /** Function called by associated memory device (cache, memory, iodevice)
-        in order to send a timing request to the port.  Simply calls the peer
-        port receive function.
-        @return This function returns if the send was succesful in it's
-        recieve. If it was a failure, then the port will wait for a recvRetry
-        at which point it can possibly issue a successful sendTiming.  This is used in
-        case a cache has a higher priority request come in while waiting for
-        the bus to arbitrate.
-    */
-    bool sendTiming(PacketPtr pkt) { return peer->recvTiming(pkt); }
+    void sendFunctional(PacketPtr pkt) { return peer->recvFunctional(pkt); }
 
-    /** Function called by the associated device to send an atomic
-     *   access, an access in which the data is moved and the state is
-     *   updated in one cycle, without interleaving with other memory
-     *   accesses.  Returns estimated latency of access.
-     */
-    Tick sendAtomic(PacketPtr pkt)
-        { return peer->recvAtomic(pkt); }
+};
 
-    /** Function called by the associated device to send a functional access,
-        an access in which the data is instantly updated everywhere in the
-        memory system, without affecting the current state of any block or
-        moving the block.
-    */
-    void sendFunctional(PacketPtr pkt)
-        { return peer->recvFunctional(pkt); }
+/** Forward declaration */
+class SlavePort;
+
+/**
+ * A MasterPort is a specialisation of a port. In addition to the
+ * basic functionality of sending packets to its slave peer, it also
+ * has functions specific to a master, e.g. to receive range changes
+ * or determine if the port is snooping or not.
+ */
+class MasterPort : public Port
+{
+
+  private:
+
+    SlavePort* _slavePort;
+
+  public:
+
+    MasterPort(const std::string& name, MemObject* owner);
+    virtual ~MasterPort();
+
+    void bind(SlavePort& slave_port);
+    SlavePort& getSlavePort() const;
+    bool isConnected() const;
 
     /**
-     * Called by the associated device to send a status range to the
-     * peer interface.
+     * Called to receive an address range change from the peer slave
+     * port. the default implementation ignored the change and does
+     * nothing. Override this function in a derived class if the owner
+     * needs to be aware of he laesddress ranges, e.g. in an
+     * interconnect component like a bus.
      */
-    void sendRangeChange() const { peer->recvRangeChange(); }
+    virtual void recvRangeChange() { }
 
-    /** When a timing access doesn't return a success, some time later the
-        Retry will be sent.
-    */
-    void sendRetry() { return peer->recvRetry(); }
+    /**
+     * Determine if this master port is snooping or not. The default
+     * implementation returns false and thus tells the neighbour we
+     * are not snooping. Any master port that wants to receive snoop
+     * requests (e.g. a cache connected to a bus) has to override this
+     * function.
+     *
+     * @return true if the port should be considered a snooper
+     */
+    virtual bool isSnooping() const { return false; }
+
+    /**
+     * Called by a peer port in order to determine the block size of
+     * the owner of this port.
+     */
+    virtual unsigned deviceBlockSize() const { return 0; }
 
     /** Called by the associated device if it wishes to find out the blocksize
         of the device on attached to the peer port.
     */
-    unsigned peerBlockSize() const { return peer->deviceBlockSize(); }
+    unsigned peerBlockSize() const;
 
     /** Inject a PrintReq for the given address to print the state of
      * that address throughout the memory system.  For debugging.
@@ -231,4 +234,52 @@ class Port
     void printAddr(Addr a);
 };
 
+/**
+ * A SlavePort is a specialisation of a port. In addition to the
+ * basic functionality of sending packets to its master peer, it also
+ * has functions specific to a slave, e.g. to send range changes
+ * and get the address ranges that the port responds to.
+ */
+class SlavePort : public Port
+{
+
+  private:
+
+    MasterPort* _masterPort;
+
+  public:
+
+    SlavePort(const std::string& name, MemObject* owner);
+    virtual ~SlavePort();
+
+    void bind(MasterPort& master_port);
+    MasterPort& getMasterPort() const;
+    bool isConnected() const;
+
+    /**
+     * Called by a peer port in order to determine the block size of
+     * the owner of this port.
+     */
+    virtual unsigned deviceBlockSize() const { return 0; }
+
+    /** Called by the associated device if it wishes to find out the blocksize
+        of the device on attached to the peer port.
+    */
+    unsigned peerBlockSize() const;
+
+    /**
+     * Called by the owner to send a range change
+     */
+    void sendRangeChange() const { _masterPort->recvRangeChange(); }
+
+    /**
+     * Get a list of the non-overlapping address ranges the owner is
+     * responsible for. All slave ports must override this function
+     * and return a populated list with at least one item.
+     *
+     * @return a list of ranges responded to
+     */
+    virtual AddrRangeList getAddrRanges() = 0;
+};
+
 #endif //__MEM_PORT_HH__