bridge.cc

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#include "mem/bridge.hh"
 
#include "base/trace.hh"
#include "debug/Bridge.hh"
#include "params/Bridge.hh"
 
namespace gem5
{
 
Bridge::BridgeResponsePort::BridgeResponsePort(const std::string& _name,
                                         Bridge& _bridge,
                                         BridgeRequestPort& _memSidePort,
                                         Cycles _delay, int _resp_limit,
                                         std::vector<AddrRange> _ranges)
    : ResponsePort(_name), bridge(_bridge),
      memSidePort(_memSidePort), delay(_delay),
      ranges(_ranges.begin(), _ranges.end()),
      outstandingResponses(0), retryReq(false), respQueueLimit(_resp_limit),
      sendEvent([this]{ trySendTiming(); }, _name)
{
}
 
Bridge::BridgeRequestPort::BridgeRequestPort(const std::string& _name,
                                           Bridge& _bridge,
                                           BridgeResponsePort& _cpuSidePort,
                                           Cycles _delay, int _req_limit)
    : RequestPort(_name), bridge(_bridge),
      cpuSidePort(_cpuSidePort),
      delay(_delay), reqQueueLimit(_req_limit),
      sendEvent([this]{ trySendTiming(); }, _name)
{
}
 
Bridge::Bridge(const Params &p)
    : ClockedObject(p),
      cpuSidePort(p.name + ".cpu_side_port", *this, memSidePort,
                ticksToCycles(p.delay), p.resp_size, p.ranges),
      memSidePort(p.name + ".mem_side_port", *this, cpuSidePort,
                 ticksToCycles(p.delay), p.req_size)
{
}
 
Port &
Bridge::getPort(const std::string &if_name, PortID idx)
{
    if (if_name == "mem_side_port")
        return memSidePort;
    else if (if_name == "cpu_side_port")
        return cpuSidePort;
    else
        // pass it along to our super class
        return ClockedObject::getPort(if_name, idx);
}
 
void
Bridge::init()
{
    // make sure both sides are connected and have the same block size
    if (!cpuSidePort.isConnected() || !memSidePort.isConnected())
        fatal("Both ports of a bridge must be connected.\n");
 
    // notify the request side  of our address ranges
    cpuSidePort.sendRangeChange();
}
 
bool
Bridge::BridgeResponsePort::respQueueFull() const
{
    return outstandingResponses == respQueueLimit;
}
 
bool
Bridge::BridgeRequestPort::reqQueueFull() const
{
    return transmitList.size() == reqQueueLimit;
}
 
bool
Bridge::BridgeRequestPort::recvTimingResp(PacketPtr pkt)
{
    // all checks are done when the request is accepted on the response
    // side, so we are guaranteed to have space for the response
    DPRINTF(Bridge, "recvTimingResp: %s addr 0x%x\n",
            pkt->cmdString(), pkt->getAddr());
 
    DPRINTF(Bridge, "Request queue size: %d\n", transmitList.size());
 
    // technically the packet only reaches us after the header delay,
    // and typically we also need to deserialise any payload (unless
    // the two sides of the bridge are synchronous)
    Tick receive_delay = pkt->headerDelay + pkt->payloadDelay;
    pkt->headerDelay = pkt->payloadDelay = 0;
 
    cpuSidePort.schedTimingResp(pkt, bridge.clockEdge(delay) +
                              receive_delay);
 
    return true;
}
 
bool
Bridge::BridgeResponsePort::recvTimingReq(PacketPtr pkt)
{
    DPRINTF(Bridge, "recvTimingReq: %s addr 0x%x\n",
            pkt->cmdString(), pkt->getAddr());
 
    panic_if(pkt->cacheResponding(), "Should not see packets where cache "
             "is responding");
 
    // we should not get a new request after committing to retry the
    // current one, but unfortunately the CPU violates this rule, so
    // simply ignore it for now
    if (retryReq)
        return false;
 
    DPRINTF(Bridge, "Response queue size: %d outresp: %d\n",
            transmitList.size(), outstandingResponses);
 
    // if the request queue is full then there is no hope
    if (memSidePort.reqQueueFull()) {
        DPRINTF(Bridge, "Request queue full\n");
        retryReq = true;
    } else {
        // look at the response queue if we expect to see a response
        bool expects_response = pkt->needsResponse();
        if (expects_response) {
            if (respQueueFull()) {
                DPRINTF(Bridge, "Response queue full\n");
                retryReq = true;
            } else {
                // ok to send the request with space for the response
                DPRINTF(Bridge, "Reserving space for response\n");
                assert(outstandingResponses != respQueueLimit);
                ++outstandingResponses;
 
                // no need to set retryReq to false as this is already the
                // case
            }
        }
 
        if (!retryReq) {
            // technically the packet only reaches us after the header
            // delay, and typically we also need to deserialise any
            // payload (unless the two sides of the bridge are
            // synchronous)
            Tick receive_delay = pkt->headerDelay + pkt->payloadDelay;
            pkt->headerDelay = pkt->payloadDelay = 0;
 
            memSidePort.schedTimingReq(pkt, bridge.clockEdge(delay) +
                                      receive_delay);
        }
    }
 
    // remember that we are now stalling a packet and that we have to
    // tell the sending requestor to retry once space becomes available,
    // we make no distinction whether the stalling is due to the
    // request queue or response queue being full
    return !retryReq;
}
 
void
Bridge::BridgeResponsePort::retryStalledReq()
{
    if (retryReq) {
        DPRINTF(Bridge, "Request waiting for retry, now retrying\n");
        retryReq = false;
        sendRetryReq();
    }
}
 
void
Bridge::BridgeRequestPort::schedTimingReq(PacketPtr pkt, Tick when)
{
    // If we're about to put this packet at the head of the queue, we
    // need to schedule an event to do the transmit.  Otherwise there
    // should already be an event scheduled for sending the head
    // packet.
    if (transmitList.empty()) {
        bridge.schedule(sendEvent, when);
    }
 
    assert(transmitList.size() != reqQueueLimit);
 
    transmitList.emplace_back(pkt, when);
}
 
 
void
Bridge::BridgeResponsePort::schedTimingResp(PacketPtr pkt, Tick when)
{
    // If we're about to put this packet at the head of the queue, we
    // need to schedule an event to do the transmit.  Otherwise there
    // should already be an event scheduled for sending the head
    // packet.
    if (transmitList.empty()) {
        bridge.schedule(sendEvent, when);
    }
 
    transmitList.emplace_back(pkt, when);
}
 
void
Bridge::BridgeRequestPort::trySendTiming()
{
    assert(!transmitList.empty());
 
    DeferredPacket req = transmitList.front();
 
    assert(req.tick <= curTick());
 
    PacketPtr pkt = req.pkt;
 
    DPRINTF(Bridge, "trySend request addr 0x%x, queue size %d\n",
            pkt->getAddr(), transmitList.size());
 
    if (sendTimingReq(pkt)) {
        // send successful
        transmitList.pop_front();
        DPRINTF(Bridge, "trySend request successful\n");
 
        // If there are more packets to send, schedule event to try again.
        if (!transmitList.empty()) {
            DeferredPacket next_req = transmitList.front();
            DPRINTF(Bridge, "Scheduling next send\n");
            bridge.schedule(sendEvent, std::max(next_req.tick,
                                                bridge.clockEdge()));
        }
 
        // if we have stalled a request due to a full request queue,
        // then send a retry at this point, also note that if the
        // request we stalled was waiting for the response queue
        // rather than the request queue we might stall it again
        cpuSidePort.retryStalledReq();
    }
 
    // if the send failed, then we try again once we receive a retry,
    // and therefore there is no need to take any action
}
 
void
Bridge::BridgeResponsePort::trySendTiming()
{
    assert(!transmitList.empty());
 
    DeferredPacket resp = transmitList.front();
 
    assert(resp.tick <= curTick());
 
    PacketPtr pkt = resp.pkt;
 
    DPRINTF(Bridge, "trySend response addr 0x%x, outstanding %d\n",
            pkt->getAddr(), outstandingResponses);
 
    if (sendTimingResp(pkt)) {
        // send successful
        transmitList.pop_front();
        DPRINTF(Bridge, "trySend response successful\n");
 
        assert(outstandingResponses != 0);
        --outstandingResponses;
 
        // If there are more packets to send, schedule event to try again.
        if (!transmitList.empty()) {
            DeferredPacket next_resp = transmitList.front();
            DPRINTF(Bridge, "Scheduling next send\n");
            bridge.schedule(sendEvent, std::max(next_resp.tick,
                                                bridge.clockEdge()));
        }
 
        // if there is space in the request queue and we were stalling
        // a request, it will definitely be possible to accept it now
        // since there is guaranteed space in the response queue
        if (!memSidePort.reqQueueFull() && retryReq) {
            DPRINTF(Bridge, "Request waiting for retry, now retrying\n");
            retryReq = false;
            sendRetryReq();
        }
    }
 
    // if the send failed, then we try again once we receive a retry,
    // and therefore there is no need to take any action
}
 
void
Bridge::BridgeRequestPort::recvReqRetry()
{
    trySendTiming();
}
 
void
Bridge::BridgeResponsePort::recvRespRetry()
{
    trySendTiming();
}
 
Tick
Bridge::BridgeResponsePort::recvAtomic(PacketPtr pkt)
{
    panic_if(pkt->cacheResponding(), "Should not see packets where cache "
             "is responding");
 
    return delay * bridge.clockPeriod() + memSidePort.sendAtomic(pkt);
}
 
Tick
Bridge::BridgeResponsePort::recvAtomicBackdoor(
    PacketPtr pkt, MemBackdoorPtr &backdoor)
{
    return delay * bridge.clockPeriod() + memSidePort.sendAtomicBackdoor(
        pkt, backdoor);
}
 
void
Bridge::BridgeResponsePort::recvFunctional(PacketPtr pkt)
{
    pkt->pushLabel(name());
 
    // check the response queue
    for (auto i = transmitList.begin();  i != transmitList.end(); ++i) {
        if (pkt->trySatisfyFunctional((*i).pkt)) {
            pkt->makeResponse();
            return;
        }
    }
 
    // also check the request port's request queue
    if (memSidePort.trySatisfyFunctional(pkt)) {
        return;
    }
 
    pkt->popLabel();
 
    // fall through if pkt still not satisfied
    memSidePort.sendFunctional(pkt);
}
 
void
Bridge::BridgeResponsePort::recvMemBackdoorReq(
    const MemBackdoorReq &req, MemBackdoorPtr &backdoor)
{
    memSidePort.sendMemBackdoorReq(req, backdoor);
}
 
bool
Bridge::BridgeRequestPort::trySatisfyFunctional(PacketPtr pkt)
{
    bool found = false;
    auto i = transmitList.begin();
 
    while (i != transmitList.end() && !found) {
        if (pkt->trySatisfyFunctional((*i).pkt)) {
            pkt->makeResponse();
            found = true;
        }
        ++i;
    }
 
    return found;
}
 
AddrRangeList
Bridge::BridgeResponsePort::getAddrRanges() const
{
    return ranges;
}
 
} // namespace gem5