MEM: Remove the Broadcast destination from the packet

This patch simplifies the packet by removing the broadcast flag and
instead more firmly relying on (and enforcing) the semantics of
transactions in the classic memory system, i.e. request packets are
routed from a master to a slave based on the address, and when they
are created they have neither a valid source, nor destination. On
their way to the slave, the request packet is updated with a source
field for all modules that multiplex packets from multiple master
(e.g. a bus). When a request packet is turned into a response packet
(at the final slave), it moves the potentially populated source field
to the destination field, and the response packet is routed through
any multiplexing components back to the master based on the
destination field.

Modules that connect multiplexing components, such as caches and
bridges store any existing source and destination field in the sender
state as a stack (just as before).

The packet constructor is simplified in that there is no longer a need
to pass the Packet::Broadcast as the destination (this was always the
case for the classic memory system). In the case of Ruby, rather than
using the parameter to the constructor we now rely on setDest, as
there is already another three-argument constructor in the packet
class.

In many places where the packet information was printed as part of
DPRINTFs, request packets would be printed with a numeric "dest" that
would always be -1 (Broadcast) and that field is now removed from the
printing.

1 files changed, 10 insertions, 7 deletions

diff --git a/src/mem/bridge.cc b/src/mem/bridge.cc
index 4dcb2a537..ddbc154c0 100644
--- a/src/mem/bridge.cc
+++ b/src/mem/bridge.cc
@@ -144,9 +144,8 @@ Bridge::BridgeMasterPort::recvTiming(PacketPtr pkt)
 
     // all checks are done when the request is accepted on the slave
     // side, so we are guaranteed to have space for the response
-
-    DPRINTF(BusBridge, "recvTiming: src %d dest %d addr 0x%x\n",
-            pkt->getSrc(), pkt->getDest(), pkt->getAddr());
+    DPRINTF(BusBridge, "recvTiming: response %s addr 0x%x\n",
+            pkt->cmdString(), pkt->getAddr());
 
     DPRINTF(BusBridge, "Request queue size: %d\n", requestQueue.size());
 
@@ -161,8 +160,9 @@ Bridge::BridgeSlavePort::recvTiming(PacketPtr pkt)
     // should only see requests on the slave side
     assert(pkt->isRequest());
 
-    DPRINTF(BusBridge, "recvTiming: src %d dest %d addr 0x%x\n",
-            pkt->getSrc(), pkt->getDest(), pkt->getAddr());
+
+    DPRINTF(BusBridge, "recvTiming: request %s addr 0x%x\n",
+            pkt->cmdString(), pkt->getAddr());
 
     DPRINTF(BusBridge, "Response queue size: %d outresp: %d\n",
             responseQueue.size(), outstandingResponses);
@@ -277,6 +277,9 @@ Bridge::BridgeSlavePort::queueForSendTiming(PacketPtr pkt)
     // from original request
     buf->fixResponse(pkt);
 
+    // the bridge assumes that at least one bus has set the
+    // destination field of the packet
+    assert(pkt->isDestValid());
     DPRINTF(BusBridge, "response, new dest %d\n", pkt->getDest());
     delete buf;
 
@@ -304,8 +307,8 @@ Bridge::BridgeMasterPort::trySend()
 
     PacketPtr pkt = buf->pkt;
 
-    DPRINTF(BusBridge, "trySend: origSrc %d dest %d addr 0x%x\n",
-            buf->origSrc, pkt->getDest(), pkt->getAddr());
+    DPRINTF(BusBridge, "trySend: origSrc %d addr 0x%x\n",
+            buf->origSrc, pkt->getAddr());
 
     // If the send was successful, make sure sender state was set to NULL
     // otherwise we could get a NACK back of a packet that didn't expect a