bus.cc

M5,一个功能强大的多处理器系统模拟器.很多针对处理器架构,性能的研究都使用它作为模拟平台

/*
 * Copyright (c) 2006
 * The Regents of The University of Michigan
 * All Rights Reserved
 *
 * This code is part of the M5 simulator.
 *
 * Permission is granted to use, copy, create derivative works and
 * redistribute this software and such derivative works for any
 * purpose, so long as the copyright notice above, this grant of
 * permission, and the disclaimer below appear in all copies made; and
 * so long as the name of The University of Michigan is not used in
 * any advertising or publicity pertaining to the use or distribution
 * of this software without specific, written prior authorization.
 *
 * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION FROM THE
 * UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY PURPOSE, AND
 * WITHOUT WARRANTY BY THE UNIVERSITY OF MICHIGAN OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE. THE REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE
 * LIABLE FOR ANY DAMAGES, INCLUDING DIRECT, SPECIAL, INDIRECT,
 * INCIDENTAL, OR CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM
 * ARISING OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
 * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGES.
 *
 * Authors: Ali G. Saidi
 */

/**
 * @file
 * Definition of a bus object.
 */

#include <algorithm>
#include <limits>

#include "base/misc.hh"
#include "base/trace.hh"
#include "mem/bus.hh"

Port *
Bus::getPort(const std::string &if_name, int idx)
{
    if (if_name == "default") {
        if (defaultPort == NULL) {
            defaultPort = new BusPort(csprintf("%s-default",name()), this,
                                      defaultId);
            cachedBlockSizeValid = false;
            return defaultPort;
        } else
            fatal("Default port already set\n");
    }
    int id;
    if (if_name == "functional") {
        if (!funcPort) {
            id = maxId++;
            funcPort = new BusPort(csprintf("%s-p%d-func", name(), id), this, id);
            funcPortId = id;
            interfaces[id] = funcPort;
        }
        return funcPort;
    }

    // if_name ignored?  forced to be empty?
    id = maxId++;
    assert(maxId < std::numeric_limits<typeof(maxId)>::max());
    BusPort *bp = new BusPort(csprintf("%s-p%d", name(), id), this, id);
    interfaces[id] = bp;
    cachedBlockSizeValid = false;
    return bp;
}

void
Bus::deletePortRefs(Port *p)
{

    BusPort *bp =  dynamic_cast<BusPort*>(p);
    if (bp == NULL)
        panic("Couldn't convert Port* to BusPort*\n");
    // If this is our one functional port
    if (funcPort == bp)
        return;
    interfaces.erase(bp->getId());
    clearBusCache();
    delete bp;
}

/** Get the ranges of anyone other buses that we are connected to. */
void
Bus::init()
{
    m5::hash_map<short,BusPort*>::iterator intIter;

    for (intIter = interfaces.begin(); intIter != interfaces.end(); intIter++)
        intIter->second->sendStatusChange(Port::RangeChange);
}

Bus::BusFreeEvent::BusFreeEvent(Bus *_bus) : Event(&mainEventQueue), bus(_bus)
{}

void Bus::BusFreeEvent::process()
{
    bus->recvRetry(-1);
}

const char * Bus::BusFreeEvent::description() const
{
    return "bus became available";
}

void Bus::preparePacket(PacketPtr pkt, Tick & headerTime)
{
    //Bring tickNextIdle up to the present tick
    //There is some potential ambiguity where a cycle starts, which might make
    //a difference when devices are acting right around a cycle boundary. Using
    //a < allows things which happen exactly on a cycle boundary to take up
    //only the following cycle. Anything that happens later will have to "wait"
    //for the end of that cycle, and then start using the bus after that.
    if (tickNextIdle < curTick) {
        tickNextIdle = curTick;
        if (tickNextIdle % clock != 0)
            tickNextIdle = curTick - (curTick % clock) + clock;
    }

    headerTime = tickNextIdle + headerCycles * clock;

    // The packet will be sent. Figure out how long it occupies the bus, and
    // how much of that time is for the first "word", aka bus width.
    int numCycles = 0;
    if (pkt->hasData()) {
        // If a packet has data, it needs ceil(size/width) cycles to send it
        int dataSize = pkt->getSize();
        numCycles += dataSize/width;
        if (dataSize % width)
            numCycles++;
    }

    // The first word will be delivered after the current tick, the delivery
    // of the address if any, and one bus cycle to deliver the data
    pkt->firstWordTime = headerTime + clock;

    pkt->finishTime = headerTime + numCycles * clock;
}

void Bus::occupyBus(Tick until)
{
    tickNextIdle = until;

    if (!busIdle.scheduled()) {
        busIdle.schedule(tickNextIdle);
    } else {
        busIdle.reschedule(tickNextIdle);
    }
    DPRINTF(Bus, "The bus is now occupied from tick %d to %d\n",
            curTick, tickNextIdle);
}

/** Function called by the port when the bus is receiving a Timing
 * transaction.*/
bool
Bus::recvTiming(PacketPtr pkt)
{
    short src = pkt->getSrc();

    BusPort *src_port;
    if (src == defaultId)
        src_port = defaultPort;
    else {
        src_port = checkBusCache(src);
        if (src_port == NULL) {
            src_port = interfaces[src];
            updateBusCache(src, src_port);
        }
    }

    // If the bus is busy, or other devices are in line ahead of the current
    // one, put this device on the retry list.
    if (!pkt->isExpressSnoop() &&
        (tickNextIdle > curTick ||
         (retryList.size() && (!inRetry || src_port != retryList.front()))))
    {
        addToRetryList(src_port);
        DPRINTF(Bus, "recvTiming: src %d dst %d %s 0x%x BUSY\n",
                src, pkt->getDest(), pkt->cmdString(), pkt->getAddr());
        return false;
    }

    DPRINTF(Bus, "recvTiming: src %d dst %d %s 0x%x\n",
            src, pkt->getDest(), pkt->cmdString(), pkt->getAddr());

    Tick headerTime = 0;

    if (!pkt->isExpressSnoop()) {
        preparePacket(pkt, headerTime);
    }

    short dest = pkt->getDest();
    int dest_port_id;
    Port *dest_port;

    if (dest == Packet::Broadcast) {
        dest_port_id = findPort(pkt->getAddr());
        dest_port = (dest_port_id == defaultId) ?
            defaultPort : interfaces[dest_port_id];
        SnoopIter s_end = snoopPorts.end();
        for (SnoopIter s_iter = snoopPorts.begin(); s_iter != s_end; s_iter++) {
            BusPort *p = *s_iter;
            if (p != dest_port && p != src_port) {
                // cache is not allowed to refuse snoop
                bool success M5_VAR_USED = p->sendTiming(pkt);
                assert(success);
            }
        }
    } else {
        assert(dest >= 0 && dest < maxId);
        assert(dest != src); // catch infinite loops
        dest_port_id = dest;
        if (dest_port_id == defaultId)
            dest_port = defaultPort;
        else {
            dest_port = checkBusCache(dest);
            if (dest_port == NULL) {
                dest_port = interfaces[dest_port_id];
	    // updateBusCache(dest_port_id, dest_port);
            }
        }
        dest_port = (dest_port_id == defaultId) ?
            defaultPort : interfaces[dest_port_id];
    }

    if (dest_port_id == src) {
        // Must be forwarded snoop up from below...
        assert(dest == Packet::Broadcast);
        assert(src != defaultId); // catch infinite loops
    } else {
        // send to actual target
        if (!dest_port->sendTiming(pkt))  {
            // Packet not successfully sent. Leave or put it on the retry list.
            // illegal to block responses... can lead to deadlock
            assert(!pkt->isResponse());
            DPRINTF(Bus, "recvTiming: src %d dst %d %s 0x%x TGT RETRY\n",
                    src, pkt->getDest(), pkt->cmdString(), pkt->getAddr());
            addToRetryList(src_port);
            if (!pkt->isExpressSnoop()) {
                occupyBus(headerTime);
            }
            return false;
        }
        // send OK, fall through
    }

    if (!pkt->isExpressSnoop()) {
        occupyBus(pkt->finishTime);
    }

    // Packet was successfully sent.
    // Also take care of retries
    if (inRetry) {
        DPRINTF(Bus, "Remove retry from list %d\n", src);
        retryList.front()->onRetryList(false);
        retryList.pop_front();
        inRetry = false;
    }
    return true;
}

void
Bus::recvRetry(int id)
{
    // If there's anything waiting, and the bus isn't busy...
    if (retryList.size() && curTick >= tickNextIdle) {
        //retryingPort = retryList.front();
        inRetry = true;
        DPRINTF(Bus, "Sending a retry to %s\n", retryList.front()->getPeer()->name());
        retryList.front()->sendRetry();
        // If inRetry is still true, sendTiming wasn't called
        if (inRetry)
        {
            retryList.front()->onRetryList(false);
            retryList.pop_front();
            inRetry = false;

            //Bring tickNextIdle up to the present
            while (tickNextIdle < curTick)
                tickNextIdle += clock;

            //Burn a cycle for the missed grant.
            tickNextIdle += clock;

            busIdle.reschedule(tickNextIdle, true);
        }
    }
    //If we weren't able to drain before, we might be able to now.
    if (drainEvent && retryList.size() == 0 && curTick >= tickNextIdle) {
        drainEvent->process();
        // Clear the drain event once we're done with it.
        drainEvent = NULL;
    }
}

int
Bus::findPort(Addr addr)
{
    /* An interval tree would be a better way to do this. --ali. */
    int dest_id = -1;

    dest_id = checkPortCache(addr);
    if (dest_id == -1) {
        PortIter i = portMap.find(RangeSize(addr,1));
        if (i != portMap.end()) {
            dest_id = i->second;
            updatePortCache(dest_id, i->first.start, i->first.end);
        }
    }

    // Check if this matches the default range
    if (dest_id == -1) {
        AddrRangeIter a_end = defaultRange.end();
        for (AddrRangeIter i = defaultRange.begin(); i != a_end; i++) {
            if (*i == addr) {
                DPRINTF(Bus, "  found addr %#llx on default\n", addr);