mem: Relax packet src/dest check and shift onus to crossbar

This patch allows objects to get the src/dest of a packet even if it
is not set to a valid port id. This simplifies (ab)using the bridge as
a buffer and latency adapter in situations where the neighbouring
MemObjects are not crossbars.

The checks that were done in the packet are now shifted to the
crossbar where the fields are used to index into the port
arrays. Thus, the carrier of the information is not burdened with
checking, and the crossbar can check not only that the destination is
set, but also that the port index is within limits.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/mem/noncoherent_xbar.cc b/src/mem/noncoherent_xbar.cc
index bc51be5a2..476b8314f 100644
--- a/src/mem/noncoherent_xbar.cc
+++ b/src/mem/noncoherent_xbar.cc
@@ -171,6 +171,8 @@ NoncoherentXBar::recvTimingResp(PacketPtr pkt, PortID master_port_id)
 
     // determine the destination based on what is stored in the packet
     PortID slave_port_id = pkt->getDest();
+    assert(slave_port_id != InvalidPortID);
+    assert(slave_port_id < respLayers.size());
 
     // test if the layer should be considered occupied for the current
     // port