/**
* @file
- * Declaration of the Packet Class, a packet is a transaction occuring
- * between a single level of the memory heirarchy (ie L1->L2).
+ * Declaration of the Packet class.
*/
#ifndef __MEM_PACKET_HH__
typedef uint8_t* PacketDataPtr;
/**
- * A Packet is the structure to handle requests between two levels
- * of the memory system. The Request is a global object that trancends
- * all of the memory heirarchy, but at each levels interface a packet
- * is created to transfer data/requests. For example, a request would
- * be used to initiate a request to go to memory/IOdevices, as the request
- * passes through the memory system several packets will be created. One
- * will be created to go between the L1 and L2 caches and another to go to
- * the next level and so forth.
- *
- * Packets are assumed to be returned in the case of a single response. If
- * the transaction has no response, then the consumer will delete the packet.
+ * A Packet is used to encapsulate a transfer between two objects in
+ * the memory system (e.g., the L1 and L2 cache). (In contrast, a
+ * single Request travels all the way from the requester to the
+ * ultimate destination and back, possibly being conveyed by several
+ * different Packets along the way.)
*/
class Packet
{
private:
- /** A pointer to the data being transfered. It can be differnt sizes
- at each level of the heirarchy so it belongs in the packet,
- not request. This may or may not be populated when a responder recieves
- the packet. If not populated it memory should be allocated.
+ /** A pointer to the data being transfered. It can be differnt
+ * sizes at each level of the heirarchy so it belongs in the
+ * packet, not request. This may or may not be populated when a
+ * responder recieves the packet. If not populated it memory
+ * should be allocated.
*/
PacketDataPtr data;
- /** Is the data pointer set to a value that shouldn't be freed when the
- * packet is destroyed? */
+ /** Is the data pointer set to a value that shouldn't be freed
+ * when the packet is destroyed? */
bool staticData;
- /** The data pointer points to a value that should be freed when the packet
- * is destroyed. */
+ /** The data pointer points to a value that should be freed when
+ * the packet is destroyed. */
bool dynamicData;
- /** the data pointer points to an array (thus delete [] ) needs to be called
- * on it rather than simply delete.*/
+ /** the data pointer points to an array (thus delete [] ) needs to
+ * be called on it rather than simply delete.*/
bool arrayData;
- /** The address of the request, could be virtual or physical (depending on
- cache configurations). */
+ /** The address of the request. This address could be virtual or
+ * physical, depending on the system configuration. */
Addr addr;
- /** Indicates the size of the request. */
+ /** The size of the request or transfer. */
int size;
- /** A index of the source of the transaction. */
+ /** Device address (e.g., bus ID) of the source of the
+ * transaction. The source is not responsible for setting this
+ * field; it is set implicitly by the interconnect when the
+ * packet * is first sent. */
short src;
- /** A index to the destination of the transaction. */
+ /** Device address (e.g., bus ID) of the destination of the
+ * transaction. The special value Broadcast indicates that the
+ * packet should be routed based on its address. This field is
+ * initialized in the constructor and is thus always valid
+ * (unlike * addr, size, and src). */
short dest;
+ /** Is the 'addr' field valid? */
bool addrValid;
+ /** Is the 'size' field valid? */
bool sizeValid;
+ /** Is the 'src' field valid? */
bool srcValid;
public:
+ /** The special destination address indicating that the packet
+ * should be routed based on its address. */
static const short Broadcast = -1;
- /** A pointer to the overall request. */
+ /** A pointer to the original request. */
RequestPtr req;
+ /** A virtual base opaque structure used to hold coherence-related
+ * state. A specific subclass would be derived from this to
+ * carry state specific to a particular coherence protocol. */
class CoherenceState {
public:
virtual ~CoherenceState() {}
};
- /** A virtual base opaque structure used to hold
- coherence status messages. */
- CoherenceState *coherence; // virtual base opaque,
- // assert(dynamic_cast<Foo>) etc.
-
+ /** This packet's coherence state. Caches should use
+ * dynamic_cast<> to cast to the state appropriate for the
+ * system's coherence protocol. */
+ CoherenceState *coherence;
+
+ /** A virtual base opaque structure used to hold state associated
+ * with the packet but specific to the sending device (e.g., an
+ * MSHR). A pointer to this state is returned in the packet's
+ * response so that the sender can quickly look up the state
+ * needed to process it. A specific subclass would be derived
+ * from this to carry state specific to a particular sending
+ * device. */
class SenderState {
public:
virtual ~SenderState() {}
};
- /** A virtual base opaque structure used to hold the senders state. */
- SenderState *senderState; // virtual base opaque,
- // assert(dynamic_cast<Foo>) etc.
+ /** This packet's sender state. Devices should use dynamic_cast<>
+ * to cast to the state appropriate to the sender. */
+ SenderState *senderState;
private:
/** List of command attributes. */
WriteResp = IsWrite | IsResponse
};
+ /** Return the string name of the cmd field (for debugging and
+ * tracing). */
const std::string &cmdString() const;
- /** The command of the transaction. */
+ /** The command field of the packet. */
Command cmd;
bool isRead() { return (cmd & IsRead) != 0; }
bool isResponse() { return (cmd & IsResponse) != 0; }
bool needsResponse() { return (cmd & NeedsResponse) != 0; }
- void makeTimingResponse() {
- assert(needsResponse());
- int icmd = (int)cmd;
- icmd &= ~(IsRequest | NeedsResponse);
- icmd |= IsResponse;
- cmd = (Command)icmd;
- dest = src;
- srcValid = false;
- }
-
- /** The time this request was responded to. Used to calculate latencies. */
- Tick time;
-
- /** The result of a particular packets request. */
+ /** Possible results of a packet's request. */
enum Result
{
Success,
Unknown
};
- /** The result of the packet transaction. */
+ /** The result of this packet's request. */
Result result;
/** Accessor function that returns the source index of the packet. */
int getSize() const { assert(sizeValid); return size; }
void setSize(int _size) { size = _size; sizeValid = true; }
-
+ /** Constructor. Note that a Request object must be constructed
+ * first, but the Requests's physical address and size fields
+ * need not be valid. The command and destination addresses
+ * must be supplied. */
Packet(Request *_req, Command _cmd, short _dest)
: data(NULL), staticData(false), dynamicData(false), arrayData(false),
addr(_req->paddr), size(_req->size), dest(_dest),
addrValid(_req->validPaddr), sizeValid(_req->validSize),
srcValid(false),
req(_req), coherence(NULL), senderState(NULL), cmd(_cmd),
- time(curTick), result(Unknown)
+ result(Unknown)
{
}
+ /** Destructor. */
~Packet()
{ deleteData(); }
-
- /** Minimally reset a packet so something like simple cpu can reuse it. */
- void reset();
-
+ /** Reinitialize packet address and size from the associated
+ * Request object, and reset other fields that may have been
+ * modified by a previous transaction. Typically called when a
+ * statically allocated Request/Packet pair is reused for
+ * multiple transactions. */
void reinitFromRequest() {
- if (req->validPaddr) setAddr(req->paddr);
- if (req->validSize) setSize(req->size);
+ assert(req->validPaddr);
+ setAddr(req->paddr);
+ assert(req->validSize);
+ setSize(req->size);
+ result = Unknown;
+ if (dynamicData) {
+ deleteData();
+ dynamicData = false;
+ arrayData = false;
+ }
+ }
+
+ /** Take a request packet and modify it in place to be suitable
+ * for returning as a response to that request. Used for timing
+ * accesses only. For atomic and functional accesses, the
+ * request packet is always implicitly passed back *without*
+ * modifying the command or destination fields, so this function
+ * should not be called. */
+ void makeTimingResponse() {
+ assert(needsResponse());
+ int icmd = (int)cmd;
+ icmd &= ~(IsRequest | NeedsResponse);
+ icmd |= IsResponse;
+ cmd = (Command)icmd;
+ dest = src;
+ srcValid = false;
}
/** Set the data pointer to the following value that should not be freed. */
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