mem: Rename Bus to XBar to better reflect its behaviour

This patch changes the name of the Bus classes to XBar to better
reflect the actual timing behaviour. The actual instances in the
config scripts are not renamed, and remain as e.g. iobus or membus.

As part of this renaming, the code has also been clean up slightly,
making use of range-based for loops and tidying up some comments. The
only changes outside the bus/crossbar code is due to the delay
variables in the packet.

--HG--
rename : src/mem/Bus.py => src/mem/XBar.py
rename : src/mem/coherent_bus.cc => src/mem/coherent_xbar.cc
rename : src/mem/coherent_bus.hh => src/mem/coherent_xbar.hh
rename : src/mem/noncoherent_bus.cc => src/mem/noncoherent_xbar.cc
rename : src/mem/noncoherent_bus.hh => src/mem/noncoherent_xbar.hh
rename : src/mem/bus.cc => src/mem/xbar.cc
rename : src/mem/bus.hh => src/mem/xbar.hh

1 files changed, 813 insertions, 0 deletions

diff --git a/src/mem/coherent_xbar.cc b/src/mem/coherent_xbar.cc
new file mode 100644
index 000000000..ce5116de9
--- /dev/null
+++ b/src/mem/coherent_xbar.cc
@@ -0,0 +1,813 @@
+/*
+ * Copyright (c) 2011-2014 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
+ * Copyright (c) 2006 The Regents of The University of Michigan
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Ali Saidi
+ *          Andreas Hansson
+ *          William Wang
+ */
+
+/**
+ * @file
+ * Definition of a crossbar object.
+ */
+
+#include "base/misc.hh"
+#include "base/trace.hh"
+#include "debug/AddrRanges.hh"
+#include "debug/CoherentXBar.hh"
+#include "mem/coherent_xbar.hh"
+#include "sim/system.hh"
+
+CoherentXBar::CoherentXBar(const CoherentXBarParams *p)
+    : BaseXBar(p), system(p->system), snoopFilter(p->snoop_filter)
+{
+    // create the ports based on the size of the master and slave
+    // vector ports, and the presence of the default port, the ports
+    // are enumerated starting from zero
+    for (int i = 0; i < p->port_master_connection_count; ++i) {
+        std::string portName = csprintf("%s.master[%d]", name(), i);
+        MasterPort* bp = new CoherentXBarMasterPort(portName, *this, i);
+        masterPorts.push_back(bp);
+        reqLayers.push_back(new ReqLayer(*bp, *this,
+                                         csprintf(".reqLayer%d", i)));
+        snoopLayers.push_back(new SnoopLayer(*bp, *this,
+                                             csprintf(".snoopLayer%d", i)));
+    }
+
+    // see if we have a default slave device connected and if so add
+    // our corresponding master port
+    if (p->port_default_connection_count) {
+        defaultPortID = masterPorts.size();
+        std::string portName = name() + ".default";
+        MasterPort* bp = new CoherentXBarMasterPort(portName, *this,
+                                                   defaultPortID);
+        masterPorts.push_back(bp);
+        reqLayers.push_back(new ReqLayer(*bp, *this, csprintf(".reqLayer%d",
+                                             defaultPortID)));
+        snoopLayers.push_back(new SnoopLayer(*bp, *this,
+                                             csprintf(".snoopLayer%d",
+                                                      defaultPortID)));
+    }
+
+    // create the slave ports, once again starting at zero
+    for (int i = 0; i < p->port_slave_connection_count; ++i) {
+        std::string portName = csprintf("%s.slave[%d]", name(), i);
+        SlavePort* bp = new CoherentXBarSlavePort(portName, *this, i);
+        slavePorts.push_back(bp);
+        respLayers.push_back(new RespLayer(*bp, *this,
+                                           csprintf(".respLayer%d", i)));
+        snoopRespPorts.push_back(new SnoopRespPort(*bp, *this));
+    }
+
+    if (snoopFilter)
+        snoopFilter->setSlavePorts(slavePorts);
+
+    clearPortCache();
+}
+
+CoherentXBar::~CoherentXBar()
+{
+    for (auto l: reqLayers)
+        delete l;
+    for (auto l: respLayers)
+        delete l;
+    for (auto l: snoopLayers)
+        delete l;
+    for (auto p: snoopRespPorts)
+        delete p;
+}
+
+void
+CoherentXBar::init()
+{
+    // the base class is responsible for determining the block size
+    BaseXBar::init();
+
+    // iterate over our slave ports and determine which of our
+    // neighbouring master ports are snooping and add them as snoopers
+    for (const auto& p: slavePorts) {
+        // check if the connected master port is snooping
+        if (p->isSnooping()) {
+            DPRINTF(AddrRanges, "Adding snooping master %s\n",
+                    p->getMasterPort().name());
+            snoopPorts.push_back(p);
+        }
+    }
+
+    if (snoopPorts.empty())
+        warn("CoherentXBar %s has no snooping ports attached!\n", name());
+}
+
+bool
+CoherentXBar::recvTimingReq(PacketPtr pkt, PortID slave_port_id)
+{
+    // determine the source port based on the id
+    SlavePort *src_port = slavePorts[slave_port_id];
+
+    // remember if the packet is an express snoop
+    bool is_express_snoop = pkt->isExpressSnoop();
+
+    // determine the destination based on the address
+    PortID master_port_id = findPort(pkt->getAddr());
+
+    // test if the crossbar should be considered occupied for the current
+    // port, and exclude express snoops from the check
+    if (!is_express_snoop && !reqLayers[master_port_id]->tryTiming(src_port)) {
+        DPRINTF(CoherentXBar, "recvTimingReq: src %s %s 0x%x BUSY\n",
+                src_port->name(), pkt->cmdString(), pkt->getAddr());
+        return false;
+    }
+
+    DPRINTF(CoherentXBar, "recvTimingReq: src %s %s expr %d 0x%x\n",
+            src_port->name(), pkt->cmdString(), is_express_snoop,
+            pkt->getAddr());
+
+    // store size and command as they might be modified when
+    // forwarding the packet
+    unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
+    unsigned int pkt_cmd = pkt->cmdToIndex();
+
+    // set the source port for routing of the response
+    pkt->setSrc(slave_port_id);
+
+    calcPacketTiming(pkt);
+    Tick packetFinishTime = pkt->lastWordDelay + curTick();
+
+    // uncacheable requests need never be snooped
+    if (!pkt->req->isUncacheable() && !system->bypassCaches()) {
+        // the packet is a memory-mapped request and should be
+        // broadcasted to our snoopers but the source
+        if (snoopFilter) {
+            // check with the snoop filter where to forward this packet
+            auto sf_res = snoopFilter->lookupRequest(pkt, *src_port);
+            packetFinishTime += sf_res.second * clockPeriod();
+            DPRINTF(CoherentXBar, "recvTimingReq: src %s %s 0x%x"\
+                    " SF size: %i lat: %i\n", src_port->name(),
+                    pkt->cmdString(), pkt->getAddr(), sf_res.first.size(),
+                    sf_res.second);
+            forwardTiming(pkt, slave_port_id, sf_res.first);
+        } else {
+            forwardTiming(pkt, slave_port_id);
+        }
+    }
+
+    // remember if we add an outstanding req so we can undo it if
+    // necessary, if the packet needs a response, we should add it
+    // as outstanding and express snoops never fail so there is
+    // not need to worry about them
+    bool add_outstanding = !is_express_snoop && pkt->needsResponse();
+
+    // keep track that we have an outstanding request packet
+    // matching this request, this is used by the coherency
+    // mechanism in determining what to do with snoop responses
+    // (in recvTimingSnoop)
+    if (add_outstanding) {
+        // we should never have an exsiting request outstanding
+        assert(outstandingReq.find(pkt->req) == outstandingReq.end());
+        outstandingReq.insert(pkt->req);
+    }
+
+    // Note: Cannot create a copy of the full packet, here.
+    MemCmd orig_cmd(pkt->cmd);
+
+    // since it is a normal request, attempt to send the packet
+    bool success = masterPorts[master_port_id]->sendTimingReq(pkt);
+
+    if (snoopFilter && !pkt->req->isUncacheable()
+        && !system->bypassCaches()) {
+        // The packet may already be overwritten by the sendTimingReq function.
+        // The snoop filter needs to see the original request *and* the return
+        // status of the send operation, so we need to recreate the original
+        // request.  Atomic mode does not have the issue, as there the send
+        // operation and the response happen instantaneously and don't need two
+        // phase tracking.
+        MemCmd tmp_cmd(pkt->cmd);
+        pkt->cmd = orig_cmd;
+        // Let the snoop filter know about the success of the send operation
+        snoopFilter->updateRequest(pkt, *src_port, !success);
+        pkt->cmd = tmp_cmd;
+    }
+
+    // if this is an express snoop, we are done at this point
+    if (is_express_snoop) {
+        assert(success);
+        snoops++;
+    } else {
+        // for normal requests, check if successful
+        if (!success)  {
+            // inhibited packets should never be forced to retry
+            assert(!pkt->memInhibitAsserted());
+
+            // if it was added as outstanding and the send failed, then
+            // erase it again
+            if (add_outstanding)
+                outstandingReq.erase(pkt->req);
+
+            // undo the calculation so we can check for 0 again
+            pkt->firstWordDelay = pkt->lastWordDelay = 0;
+
+            DPRINTF(CoherentXBar, "recvTimingReq: src %s %s 0x%x RETRY\n",
+                    src_port->name(), pkt->cmdString(), pkt->getAddr());
+
+            // update the layer state and schedule an idle event
+            reqLayers[master_port_id]->failedTiming(src_port,
+                                                    clockEdge(headerCycles));
+        } else {
+            // update the layer state and schedule an idle event
+            reqLayers[master_port_id]->succeededTiming(packetFinishTime);
+        }
+    }
+
+    // stats updates only consider packets that were successfully sent
+    if (success) {
+        pktCount[slave_port_id][master_port_id]++;
+        pktSize[slave_port_id][master_port_id] += pkt_size;
+        transDist[pkt_cmd]++;
+    }
+
+    return success;
+}
+
+bool
+CoherentXBar::recvTimingResp(PacketPtr pkt, PortID master_port_id)
+{
+    // determine the source port based on the id
+    MasterPort *src_port = masterPorts[master_port_id];
+
+    // determine the destination based on what is stored in the packet
+    PortID slave_port_id = pkt->getDest();
+
+    // test if the crossbar should be considered occupied for the
+    // current port
+    if (!respLayers[slave_port_id]->tryTiming(src_port)) {
+        DPRINTF(CoherentXBar, "recvTimingResp: src %s %s 0x%x BUSY\n",
+                src_port->name(), pkt->cmdString(), pkt->getAddr());
+        return false;
+    }
+
+    DPRINTF(CoherentXBar, "recvTimingResp: src %s %s 0x%x\n",
+            src_port->name(), pkt->cmdString(), pkt->getAddr());
+
+    // store size and command as they might be modified when
+    // forwarding the packet
+    unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
+    unsigned int pkt_cmd = pkt->cmdToIndex();
+
+    calcPacketTiming(pkt);
+    Tick packetFinishTime = pkt->lastWordDelay + curTick();
+
+    // the packet is a normal response to a request that we should
+    // have seen passing through the crossbar
+    assert(outstandingReq.find(pkt->req) != outstandingReq.end());
+
+    if (snoopFilter && !pkt->req->isUncacheable() && !system->bypassCaches()) {
+        // let the snoop filter inspect the response and update its state
+        snoopFilter->updateResponse(pkt, *slavePorts[slave_port_id]);
+    }
+
+    // remove it as outstanding
+    outstandingReq.erase(pkt->req);
+
+    // send the packet through the destination slave port
+    bool success M5_VAR_USED = slavePorts[slave_port_id]->sendTimingResp(pkt);
+
+    // currently it is illegal to block responses... can lead to
+    // deadlock
+    assert(success);
+
+    respLayers[slave_port_id]->succeededTiming(packetFinishTime);
+
+    // stats updates
+    pktCount[slave_port_id][master_port_id]++;
+    pktSize[slave_port_id][master_port_id] += pkt_size;
+    transDist[pkt_cmd]++;
+
+    return true;
+}
+
+void
+CoherentXBar::recvTimingSnoopReq(PacketPtr pkt, PortID master_port_id)
+{
+    DPRINTF(CoherentXBar, "recvTimingSnoopReq: src %s %s 0x%x\n",
+            masterPorts[master_port_id]->name(), pkt->cmdString(),
+            pkt->getAddr());
+
+    // update stats here as we know the forwarding will succeed
+    transDist[pkt->cmdToIndex()]++;
+    snoops++;
+
+    // we should only see express snoops from caches
+    assert(pkt->isExpressSnoop());
+
+    // set the source port for routing of the response
+    pkt->setSrc(master_port_id);
+
+    if (snoopFilter) {
+        // let the Snoop Filter work its magic and guide probing
+        auto sf_res = snoopFilter->lookupSnoop(pkt);
+        // No timing here: packetFinishTime += sf_res.second * clockPeriod();
+        DPRINTF(CoherentXBar, "recvTimingSnoopReq: src %s %s 0x%x"\
+                " SF size: %i lat: %i\n", masterPorts[master_port_id]->name(),
+                pkt->cmdString(), pkt->getAddr(), sf_res.first.size(),
+                sf_res.second);
+
+        // forward to all snoopers
+        forwardTiming(pkt, InvalidPortID, sf_res.first);
+    } else {
+        forwardTiming(pkt, InvalidPortID);
+    }
+
+    // a snoop request came from a connected slave device (one of
+    // our master ports), and if it is not coming from the slave
+    // device responsible for the address range something is
+    // wrong, hence there is nothing further to do as the packet
+    // would be going back to where it came from
+    assert(master_port_id == findPort(pkt->getAddr()));
+}
+
+bool
+CoherentXBar::recvTimingSnoopResp(PacketPtr pkt, PortID slave_port_id)
+{
+    // determine the source port based on the id
+    SlavePort* src_port = slavePorts[slave_port_id];
+
+    // get the destination from the packet
+    PortID dest_port_id = pkt->getDest();
+
+    // determine if the response is from a snoop request we
+    // created as the result of a normal request (in which case it
+    // should be in the outstandingReq), or if we merely forwarded
+    // someone else's snoop request
+    bool forwardAsSnoop = outstandingReq.find(pkt->req) ==
+        outstandingReq.end();
+
+    // test if the crossbar should be considered occupied for the
+    // current port, note that the check is bypassed if the response
+    // is being passed on as a normal response since this is occupying
+    // the response layer rather than the snoop response layer
+    if (forwardAsSnoop) {
+        if (!snoopLayers[dest_port_id]->tryTiming(src_port)) {
+            DPRINTF(CoherentXBar, "recvTimingSnoopResp: src %s %s 0x%x BUSY\n",
+                    src_port->name(), pkt->cmdString(), pkt->getAddr());
+            return false;
+        }
+    } else {
+        // get the master port that mirrors this slave port internally
+        MasterPort* snoop_port = snoopRespPorts[slave_port_id];
+        if (!respLayers[dest_port_id]->tryTiming(snoop_port)) {
+            DPRINTF(CoherentXBar, "recvTimingSnoopResp: src %s %s 0x%x BUSY\n",
+                    snoop_port->name(), pkt->cmdString(), pkt->getAddr());
+            return false;
+        }
+    }
+
+    DPRINTF(CoherentXBar, "recvTimingSnoopResp: src %s %s 0x%x\n",
+            src_port->name(), pkt->cmdString(), pkt->getAddr());
+
+    // store size and command as they might be modified when
+    // forwarding the packet
+    unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
+    unsigned int pkt_cmd = pkt->cmdToIndex();
+
+    // responses are never express snoops
+    assert(!pkt->isExpressSnoop());
+
+    calcPacketTiming(pkt);
+    Tick packetFinishTime = pkt->lastWordDelay + curTick();
+
+    // forward it either as a snoop response or a normal response
+    if (forwardAsSnoop) {
+        // this is a snoop response to a snoop request we forwarded,
+        // e.g. coming from the L1 and going to the L2, and it should
+        // be forwarded as a snoop response
+
+        if (snoopFilter) {
+            // update the probe filter so that it can properly track the line
+            snoopFilter->updateSnoopForward(pkt, *slavePorts[slave_port_id],
+                                            *masterPorts[dest_port_id]);
+        }
+
+        bool success M5_VAR_USED =
+            masterPorts[dest_port_id]->sendTimingSnoopResp(pkt);
+        pktCount[slave_port_id][dest_port_id]++;
+        pktSize[slave_port_id][dest_port_id] += pkt_size;
+        assert(success);
+
+        snoopLayers[dest_port_id]->succeededTiming(packetFinishTime);
+    } else {
+        // we got a snoop response on one of our slave ports,
+        // i.e. from a coherent master connected to the crossbar, and
+        // since we created the snoop request as part of recvTiming,
+        // this should now be a normal response again
+        outstandingReq.erase(pkt->req);
+
+        // this is a snoop response from a coherent master, with a
+        // destination field set on its way through the crossbar as
+        // request, hence it should never go back to where the snoop
+        // response came from, but instead to where the original
+        // request came from
+        assert(slave_port_id != dest_port_id);
+
+        if (snoopFilter) {
+            // update the probe filter so that it can properly track the line
+            snoopFilter->updateSnoopResponse(pkt, *slavePorts[slave_port_id],
+                                    *slavePorts[dest_port_id]);
+        }
+
+        DPRINTF(CoherentXBar, "recvTimingSnoopResp: src %s %s 0x%x"\
+                " FWD RESP\n", src_port->name(), pkt->cmdString(),
+                pkt->getAddr());
+
+        // as a normal response, it should go back to a master through
+        // one of our slave ports, at this point we are ignoring the
+        // fact that the response layer could be busy and do not touch
+        // its state
+        bool success M5_VAR_USED =
+            slavePorts[dest_port_id]->sendTimingResp(pkt);
+
+        // @todo Put the response in an internal FIFO and pass it on
+        // to the response layer from there
+
+        // currently it is illegal to block responses... can lead
+        // to deadlock
+        assert(success);
+
+        respLayers[dest_port_id]->succeededTiming(packetFinishTime);
+    }
+
+    // stats updates
+    transDist[pkt_cmd]++;
+    snoops++;
+
+    return true;
+}
+
+
+void
+CoherentXBar::forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id,
+                           const std::vector<SlavePort*>& dests)
+{
+    DPRINTF(CoherentXBar, "%s for %s address %x size %d\n", __func__,
+            pkt->cmdString(), pkt->getAddr(), pkt->getSize());
+
+    // snoops should only happen if the system isn't bypassing caches
+    assert(!system->bypassCaches());
+
+    unsigned fanout = 0;
+
+    for (const auto& p: dests) {
+        // we could have gotten this request from a snooping master
+        // (corresponding to our own slave port that is also in
+        // snoopPorts) and should not send it back to where it came
+        // from
+        if (exclude_slave_port_id == InvalidPortID ||
+            p->getId() != exclude_slave_port_id) {
+            // cache is not allowed to refuse snoop
+            p->sendTimingSnoopReq(pkt);
+            fanout++;
+        }
+    }
+
+    // Stats for fanout of this forward operation
+    snoopFanout.sample(fanout);
+}
+
+void
+CoherentXBar::recvRetry(PortID master_port_id)
+{
+    // responses and snoop responses never block on forwarding them,
+    // so the retry will always be coming from a port to which we
+    // tried to forward a request
+    reqLayers[master_port_id]->recvRetry();
+}
+
+Tick
+CoherentXBar::recvAtomic(PacketPtr pkt, PortID slave_port_id)
+{
+    DPRINTF(CoherentXBar, "recvAtomic: packet src %s addr 0x%x cmd %s\n",
+            slavePorts[slave_port_id]->name(), pkt->getAddr(),
+            pkt->cmdString());
+
+    unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
+    unsigned int pkt_cmd = pkt->cmdToIndex();
+
+    MemCmd snoop_response_cmd = MemCmd::InvalidCmd;
+    Tick snoop_response_latency = 0;
+
+    // uncacheable requests need never be snooped
+    if (!pkt->req->isUncacheable() && !system->bypassCaches()) {
+        // forward to all snoopers but the source
+        std::pair<MemCmd, Tick> snoop_result;
+        if (snoopFilter) {
+            // check with the snoop filter where to forward this packet
+            auto sf_res =
+                snoopFilter->lookupRequest(pkt, *slavePorts[slave_port_id]);
+            snoop_response_latency += sf_res.second * clockPeriod();
+            DPRINTF(CoherentXBar, "%s: src %s %s 0x%x"\
+                    " SF size: %i lat: %i\n", __func__,
+                    slavePorts[slave_port_id]->name(), pkt->cmdString(),
+                    pkt->getAddr(), sf_res.first.size(), sf_res.second);
+            snoop_result = forwardAtomic(pkt, slave_port_id, InvalidPortID,
+                                         sf_res.first);
+        } else {
+            snoop_result = forwardAtomic(pkt, slave_port_id);
+        }
+        snoop_response_cmd = snoop_result.first;
+        snoop_response_latency += snoop_result.second;
+    }
+
+    // even if we had a snoop response, we must continue and also
+    // perform the actual request at the destination
+    PortID master_port_id = findPort(pkt->getAddr());
+
+    // stats updates for the request
+    pktCount[slave_port_id][master_port_id]++;
+    pktSize[slave_port_id][master_port_id] += pkt_size;
+    transDist[pkt_cmd]++;
+
+    // forward the request to the appropriate destination
+    Tick response_latency = masterPorts[master_port_id]->sendAtomic(pkt);
+
+    // Lower levels have replied, tell the snoop filter
+    if (snoopFilter && !pkt->req->isUncacheable() && !system->bypassCaches() &&
+        pkt->isResponse()) {
+        snoopFilter->updateResponse(pkt, *slavePorts[slave_port_id]);
+    }
+
+    // if we got a response from a snooper, restore it here
+    if (snoop_response_cmd != MemCmd::InvalidCmd) {
+        // no one else should have responded
+        assert(!pkt->isResponse());
+        pkt->cmd = snoop_response_cmd;
+        response_latency = snoop_response_latency;
+    }
+
+    // add the response data
+    if (pkt->isResponse()) {
+        pkt_size = pkt->hasData() ? pkt->getSize() : 0;
+        pkt_cmd = pkt->cmdToIndex();
+
+        // stats updates
+        pktCount[slave_port_id][master_port_id]++;
+        pktSize[slave_port_id][master_port_id] += pkt_size;
+        transDist[pkt_cmd]++;
+    }
+
+    // @todo: Not setting first-word time
+    pkt->lastWordDelay = response_latency;
+    return response_latency;
+}
+
+Tick
+CoherentXBar::recvAtomicSnoop(PacketPtr pkt, PortID master_port_id)
+{
+    DPRINTF(CoherentXBar, "recvAtomicSnoop: packet src %s addr 0x%x cmd %s\n",
+            masterPorts[master_port_id]->name(), pkt->getAddr(),
+            pkt->cmdString());
+
+    // add the request snoop data
+    snoops++;
+
+    // forward to all snoopers
+    std::pair<MemCmd, Tick> snoop_result;
+    Tick snoop_response_latency = 0;
+    if (snoopFilter) {
+        auto sf_res = snoopFilter->lookupSnoop(pkt);
+        snoop_response_latency += sf_res.second * clockPeriod();
+        DPRINTF(CoherentXBar, "%s: src %s %s 0x%x SF size: %i lat: %i\n",
+                __func__, masterPorts[master_port_id]->name(), pkt->cmdString(),
+                pkt->getAddr(), sf_res.first.size(), sf_res.second);
+        snoop_result = forwardAtomic(pkt, InvalidPortID, master_port_id,
+                                     sf_res.first);
+    } else {
+        snoop_result = forwardAtomic(pkt, InvalidPortID);
+    }
+    MemCmd snoop_response_cmd = snoop_result.first;
+    snoop_response_latency += snoop_result.second;
+
+    if (snoop_response_cmd != MemCmd::InvalidCmd)
+        pkt->cmd = snoop_response_cmd;
+
+    // add the response snoop data
+    if (pkt->isResponse()) {
+        snoops++;
+    }
+
+    // @todo: Not setting first-word time
+    pkt->lastWordDelay = snoop_response_latency;
+    return snoop_response_latency;
+}
+
+std::pair<MemCmd, Tick>
+CoherentXBar::forwardAtomic(PacketPtr pkt, PortID exclude_slave_port_id,
+                           PortID source_master_port_id,
+                           const std::vector<SlavePort*>& dests)
+{
+    // the packet may be changed on snoops, record the original
+    // command to enable us to restore it between snoops so that
+    // additional snoops can take place properly
+    MemCmd orig_cmd = pkt->cmd;
+    MemCmd snoop_response_cmd = MemCmd::InvalidCmd;
+    Tick snoop_response_latency = 0;
+
+    // snoops should only happen if the system isn't bypassing caches
+    assert(!system->bypassCaches());
+
+    unsigned fanout = 0;
+
+    for (const auto& p: dests) {
+        // we could have gotten this request from a snooping master
+        // (corresponding to our own slave port that is also in
+        // snoopPorts) and should not send it back to where it came
+        // from
+        if (exclude_slave_port_id != InvalidPortID &&
+            p->getId() == exclude_slave_port_id)
+            continue;
+
+        Tick latency = p->sendAtomicSnoop(pkt);
+        fanout++;
+
+        // in contrast to a functional access, we have to keep on
+        // going as all snoopers must be updated even if we get a
+        // response
+        if (!pkt->isResponse())
+            continue;
+
+        // response from snoop agent
+        assert(pkt->cmd != orig_cmd);
+        assert(pkt->memInhibitAsserted());
+        // should only happen once
+        assert(snoop_response_cmd == MemCmd::InvalidCmd);
+        // save response state
+        snoop_response_cmd = pkt->cmd;
+        snoop_response_latency = latency;
+
+        if (snoopFilter) {
+            // Handle responses by the snoopers and differentiate between
+            // responses to requests from above and snoops from below
+            if (source_master_port_id != InvalidPortID) {
+                // Getting a response for a snoop from below
+                assert(exclude_slave_port_id == InvalidPortID);
+                snoopFilter->updateSnoopForward(pkt, *p,
+                             *masterPorts[source_master_port_id]);
+            } else {
+                // Getting a response for a request from above
+                assert(source_master_port_id == InvalidPortID);
+                snoopFilter->updateSnoopResponse(pkt, *p,
+                             *slavePorts[exclude_slave_port_id]);
+            }
+        }
+        // restore original packet state for remaining snoopers
+        pkt->cmd = orig_cmd;
+    }
+
+    // Stats for fanout
+    snoopFanout.sample(fanout);
+
+    // the packet is restored as part of the loop and any potential
+    // snoop response is part of the returned pair
+    return std::make_pair(snoop_response_cmd, snoop_response_latency);
+}
+
+void
+CoherentXBar::recvFunctional(PacketPtr pkt, PortID slave_port_id)
+{
+    if (!pkt->isPrint()) {
+        // don't do DPRINTFs on PrintReq as it clutters up the output
+        DPRINTF(CoherentXBar,
+                "recvFunctional: packet src %s addr 0x%x cmd %s\n",
+                slavePorts[slave_port_id]->name(), pkt->getAddr(),
+                pkt->cmdString());
+    }
+
+    // uncacheable requests need never be snooped
+    if (!pkt->req->isUncacheable() && !system->bypassCaches()) {
+        // forward to all snoopers but the source
+        forwardFunctional(pkt, slave_port_id);
+    }
+
+    // there is no need to continue if the snooping has found what we
+    // were looking for and the packet is already a response
+    if (!pkt->isResponse()) {
+        PortID dest_id = findPort(pkt->getAddr());
+
+        masterPorts[dest_id]->sendFunctional(pkt);
+    }
+}
+
+void
+CoherentXBar::recvFunctionalSnoop(PacketPtr pkt, PortID master_port_id)
+{
+    if (!pkt->isPrint()) {
+        // don't do DPRINTFs on PrintReq as it clutters up the output
+        DPRINTF(CoherentXBar,
+                "recvFunctionalSnoop: packet src %s addr 0x%x cmd %s\n",
+                masterPorts[master_port_id]->name(), pkt->getAddr(),
+                pkt->cmdString());
+    }
+
+    // forward to all snoopers
+    forwardFunctional(pkt, InvalidPortID);
+}
+
+void
+CoherentXBar::forwardFunctional(PacketPtr pkt, PortID exclude_slave_port_id)
+{
+    // snoops should only happen if the system isn't bypassing caches
+    assert(!system->bypassCaches());
+
+    for (const auto& p: snoopPorts) {
+        // we could have gotten this request from a snooping master
+        // (corresponding to our own slave port that is also in
+        // snoopPorts) and should not send it back to where it came
+        // from
+        if (exclude_slave_port_id == InvalidPortID ||
+            p->getId() != exclude_slave_port_id)
+            p->sendFunctionalSnoop(pkt);
+
+        // if we get a response we are done
+        if (pkt->isResponse()) {
+            break;
+        }
+    }
+}
+
+unsigned int
+CoherentXBar::drain(DrainManager *dm)
+{
+    // sum up the individual layers
+    unsigned int total = 0;
+    for (auto l: reqLayers)
+        total += l->drain(dm);
+    for (auto l: respLayers)
+        total += l->drain(dm);
+    for (auto l: snoopLayers)
+        total += l->drain(dm);
+    return total;
+}
+
+void
+CoherentXBar::regStats()
+{
+    // register the stats of the base class and our layers
+    BaseXBar::regStats();
+    for (auto l: reqLayers)
+        l->regStats();
+    for (auto l: respLayers)
+        l->regStats();
+    for (auto l: snoopLayers)
+        l->regStats();
+
+    snoops
+        .name(name() + ".snoops")
+        .desc("Total snoops (count)")
+    ;
+
+    snoopFanout
+        .init(0, snoopPorts.size(), 1)
+        .name(name() + ".snoop_fanout")
+        .desc("Request fanout histogram")
+    ;
+}
+
+CoherentXBar *
+CoherentXBarParams::create()
+{
+    return new CoherentXBar(this);
+}