xref: /gem5/src/mem/dram_ctrl.cc

/*
 * Copyright (c) 2010-2013 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) 2013 Amin Farmahini-Farahani
 * 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: Andreas Hansson
 *          Ani Udipi
 *          Neha Agarwal
 */

#include "base/trace.hh"
#include "base/bitfield.hh"
#include "debug/Drain.hh"
#include "debug/DRAM.hh"
#include "mem/simple_dram.hh"
#include "sim/system.hh"

using namespace std;

SimpleDRAM::SimpleDRAM(const SimpleDRAMParams* p) :
    AbstractMemory(p),
    port(name() + ".port", *this),
    retryRdReq(false), retryWrReq(false),
    rowHitFlag(false), stopReads(false), actTicks(p->activation_limit, 0),
    writeEvent(this), respondEvent(this),
    refreshEvent(this), nextReqEvent(this), drainManager(NULL),
    deviceBusWidth(p->device_bus_width), burstLength(p->burst_length),
    deviceRowBufferSize(p->device_rowbuffer_size),
    devicesPerRank(p->devices_per_rank),
    burstSize((devicesPerRank * burstLength * deviceBusWidth) / 8),
    rowBufferSize(devicesPerRank * deviceRowBufferSize),
    ranksPerChannel(p->ranks_per_channel),
    banksPerRank(p->banks_per_rank), channels(p->channels), rowsPerBank(0),
    readBufferSize(p->read_buffer_size),
    writeBufferSize(p->write_buffer_size),
    writeThresholdPerc(p->write_thresh_perc),
    tWTR(p->tWTR), tBURST(p->tBURST),
    tRCD(p->tRCD), tCL(p->tCL), tRP(p->tRP), tRAS(p->tRAS),
    tRFC(p->tRFC), tREFI(p->tREFI),
    tXAW(p->tXAW), activationLimit(p->activation_limit),
    memSchedPolicy(p->mem_sched_policy), addrMapping(p->addr_mapping),
    pageMgmt(p->page_policy),
    frontendLatency(p->static_frontend_latency),
    backendLatency(p->static_backend_latency),
    busBusyUntil(0), writeStartTime(0),
    prevArrival(0), numReqs(0)
{
    // create the bank states based on the dimensions of the ranks and
    // banks
    banks.resize(ranksPerChannel);
    for (size_t c = 0; c < ranksPerChannel; ++c) {
        banks[c].resize(banksPerRank);
    }

    // round the write threshold percent to a whole number of entries
    // in the buffer
    writeThreshold = writeBufferSize * writeThresholdPerc / 100.0;
}

void
SimpleDRAM::init()
{
    if (!port.isConnected()) {
        fatal("SimpleDRAM %s is unconnected!\n", name());
    } else {
        port.sendRangeChange();
    }

    // we could deal with plenty options here, but for now do a quick
    // sanity check
    DPRINTF(DRAM, "Burst size %d bytes\n", burstSize);

    // determine the rows per bank by looking at the total capacity
    uint64_t capacity = ULL(1) << ceilLog2(AbstractMemory::size());

    DPRINTF(DRAM, "Memory capacity %lld (%lld) bytes\n", capacity,
            AbstractMemory::size());

    columnsPerRowBuffer = rowBufferSize / burstSize;

    DPRINTF(DRAM, "Row buffer size %d bytes with %d columns per row buffer\n",
            rowBufferSize, columnsPerRowBuffer);

    rowsPerBank = capacity / (rowBufferSize * banksPerRank * ranksPerChannel);

    if (range.interleaved()) {
        if (channels != range.stripes())
            panic("%s has %d interleaved address stripes but %d channel(s)\n",
                  name(), range.stripes(), channels);

        if (addrMapping == Enums::RaBaChCo) {
            if (rowBufferSize != range.granularity()) {
                panic("Interleaving of %s doesn't match RaBaChCo address map\n",
                      name());
            }
        } else if (addrMapping == Enums::RaBaCoCh) {
            if (burstSize != range.granularity()) {
                panic("Interleaving of %s doesn't match RaBaCoCh address map\n",
                      name());
            }
        } else if (addrMapping == Enums::CoRaBaCh) {
            if (burstSize != range.granularity())
                panic("Interleaving of %s doesn't match CoRaBaCh address map\n",
                      name());
        }
    }
}

void
SimpleDRAM::startup()
{
    // print the configuration of the controller
    printParams();

    // kick off the refresh
    schedule(refreshEvent, curTick() + tREFI);
}

Tick
SimpleDRAM::recvAtomic(PacketPtr pkt)
{
    DPRINTF(DRAM, "recvAtomic: %s 0x%x\n", pkt->cmdString(), pkt->getAddr());

    // do the actual memory access and turn the packet into a response
    access(pkt);

    Tick latency = 0;
    if (!pkt->memInhibitAsserted() && pkt->hasData()) {
        // this value is not supposed to be accurate, just enough to
        // keep things going, mimic a closed page
        latency = tRP + tRCD + tCL;
    }
    return latency;
}

bool
SimpleDRAM::readQueueFull(unsigned int neededEntries) const
{
    DPRINTF(DRAM, "Read queue limit %d, current size %d, entries needed %d\n",
            readBufferSize, readQueue.size() + respQueue.size(),
            neededEntries);

    return
        (readQueue.size() + respQueue.size() + neededEntries) > readBufferSize;
}

bool
SimpleDRAM::writeQueueFull(unsigned int neededEntries) const
{
    DPRINTF(DRAM, "Write queue limit %d, current size %d, entries needed %d\n",
            writeBufferSize, writeQueue.size(), neededEntries);
    return (writeQueue.size() + neededEntries) > writeBufferSize;
}

SimpleDRAM::DRAMPacket*
SimpleDRAM::decodeAddr(PacketPtr pkt, Addr dramPktAddr, unsigned size, bool isRead)
{
    // decode the address based on the address mapping scheme, with
    // Ra, Co, Ba and Ch denoting rank, column, bank and channel,
    // respectively
    uint8_t rank;
    uint8_t bank;
    uint16_t row;

    // truncate the address to the access granularity
    Addr addr = dramPktAddr / burstSize;

    // we have removed the lowest order address bits that denote the
    // position within the column
    if (addrMapping == Enums::RaBaChCo) {
        // the lowest order bits denote the column to ensure that
        // sequential cache lines occupy the same row
        addr = addr / columnsPerRowBuffer;

        // take out the channel part of the address
        addr = addr / channels;

        // after the channel bits, get the bank bits to interleave
        // over the banks
        bank = addr % banksPerRank;
        addr = addr / banksPerRank;

        // after the bank, we get the rank bits which thus interleaves
        // over the ranks
        rank = addr % ranksPerChannel;
        addr = addr / ranksPerChannel;

        // lastly, get the row bits
        row = addr % rowsPerBank;
        addr = addr / rowsPerBank;
    } else if (addrMapping == Enums::RaBaCoCh) {
        // take out the channel part of the address
        addr = addr / channels;

        // next, the column
        addr = addr / columnsPerRowBuffer;

        // after the column bits, we get the bank bits to interleave
        // over the banks
        bank = addr % banksPerRank;
        addr = addr / banksPerRank;

        // after the bank, we get the rank bits which thus interleaves
        // over the ranks
        rank = addr % ranksPerChannel;
        addr = addr / ranksPerChannel;

        // lastly, get the row bits
        row = addr % rowsPerBank;
        addr = addr / rowsPerBank;
    } else if (addrMapping == Enums::CoRaBaCh) {
        // optimise for closed page mode and utilise maximum
        // parallelism of the DRAM (at the cost of power)

        // take out the channel part of the address, not that this has
        // to match with how accesses are interleaved between the
        // controllers in the address mapping
        addr = addr / channels;

        // start with the bank bits, as this provides the maximum
        // opportunity for parallelism between requests
        bank = addr % banksPerRank;
        addr = addr / banksPerRank;

        // next get the rank bits
        rank = addr % ranksPerChannel;
        addr = addr / ranksPerChannel;

        // next the column bits which we do not need to keep track of
        // and simply skip past
        addr = addr / columnsPerRowBuffer;

        // lastly, get the row bits
        row = addr % rowsPerBank;
        addr = addr / rowsPerBank;
    } else
        panic("Unknown address mapping policy chosen!");

    assert(rank < ranksPerChannel);
    assert(bank < banksPerRank);
    assert(row < rowsPerBank);

    DPRINTF(DRAM, "Address: %lld Rank %d Bank %d Row %d\n",
            dramPktAddr, rank, bank, row);

    // create the corresponding DRAM packet with the entry time and
    // ready time set to the current tick, the latter will be updated
    // later
    uint16_t bank_id = banksPerRank * rank + bank;
    return new DRAMPacket(pkt, isRead, rank, bank, row, bank_id, dramPktAddr,
                          size, banks[rank][bank]);
}

void
SimpleDRAM::addToReadQueue(PacketPtr pkt, unsigned int pktCount)
{
    // only add to the read queue here. whenever the request is
    // eventually done, set the readyTime, and call schedule()
    assert(!pkt->isWrite());

    assert(pktCount != 0);

    // if the request size is larger than burst size, the pkt is split into
    // multiple DRAM packets
    // Note if the pkt starting address is not aligened to burst size, the
    // address of first DRAM packet is kept unaliged. Subsequent DRAM packets
    // are aligned to burst size boundaries. This is to ensure we accurately
    // check read packets against packets in write queue.
    Addr addr = pkt->getAddr();
    unsigned pktsServicedByWrQ = 0;
    BurstHelper* burst_helper = NULL;
    for (int cnt = 0; cnt < pktCount; ++cnt) {
        unsigned size = std::min((addr | (burstSize - 1)) + 1,
                        pkt->getAddr() + pkt->getSize()) - addr;
        readPktSize[ceilLog2(size)]++;
        readBursts++;

        // First check write buffer to see if the data is already at
        // the controller
        bool foundInWrQ = false;
        for (auto i = writeQueue.begin(); i != writeQueue.end(); ++i) {
            // check if the read is subsumed in the write entry we are
            // looking at
            if ((*i)->addr <= addr &&
                (addr + size) <= ((*i)->addr + (*i)->size)) {
                foundInWrQ = true;
                servicedByWrQ++;
                pktsServicedByWrQ++;
                DPRINTF(DRAM, "Read to addr %lld with size %d serviced by "
                        "write queue\n", addr, size);
                bytesRead += burstSize;
                bytesConsumedRd += size;
                break;
            }
        }

        // If not found in the write q, make a DRAM packet and
        // push it onto the read queue
        if (!foundInWrQ) {

            // Make the burst helper for split packets
            if (pktCount > 1 && burst_helper == NULL) {
                DPRINTF(DRAM, "Read to addr %lld translates to %d "
                        "dram requests\n", pkt->getAddr(), pktCount);
                burst_helper = new BurstHelper(pktCount);
            }

            DRAMPacket* dram_pkt = decodeAddr(pkt, addr, size, true);
            dram_pkt->burstHelper = burst_helper;

            assert(!readQueueFull(1));
            rdQLenPdf[readQueue.size() + respQueue.size()]++;

            DPRINTF(DRAM, "Adding to read queue\n");

            readQueue.push_back(dram_pkt);

            // Update stats
            assert(dram_pkt->bankId < ranksPerChannel * banksPerRank);
            perBankRdReqs[dram_pkt->bankId]++;

            avgRdQLen = readQueue.size() + respQueue.size();
        }

        // Starting address of next dram pkt (aligend to burstSize boundary)
        addr = (addr | (burstSize - 1)) + 1;
    }

    // If all packets are serviced by write queue, we send the repsonse back
    if (pktsServicedByWrQ == pktCount) {
        accessAndRespond(pkt, frontendLatency);
        return;
    }

    // Update how many split packets are serviced by write queue
    if (burst_helper != NULL)
        burst_helper->burstsServiced = pktsServicedByWrQ;

    // If we are not already scheduled to get the read request out of
    // the queue, do so now
    if (!nextReqEvent.scheduled() && !stopReads) {
        DPRINTF(DRAM, "Request scheduled immediately\n");
        schedule(nextReqEvent, curTick());
    }
}

void
SimpleDRAM::processWriteEvent()
{
    assert(!writeQueue.empty());
    uint32_t numWritesThisTime = 0;

    DPRINTF(DRAM, "Beginning DRAM Writes\n");
    Tick temp1 M5_VAR_USED = std::max(curTick(), busBusyUntil);
    Tick temp2 M5_VAR_USED = std::max(curTick(), maxBankFreeAt());

    // @todo: are there any dangers with the untimed while loop?
    while (!writeQueue.empty()) {
        if (numWritesThisTime >= writeThreshold) {
            DPRINTF(DRAM, "Hit write threshold %d\n", writeThreshold);
            break;
        }

        chooseNextWrite();
        DRAMPacket* dram_pkt = writeQueue.front();
        // sanity check
        assert(dram_pkt->size <= burstSize);
        doDRAMAccess(dram_pkt);

        writeQueue.pop_front();
        delete dram_pkt;
        numWritesThisTime++;
    }

    DPRINTF(DRAM, "Completed %d writes, bus busy for %lld ticks,"\
            "banks busy for %lld ticks\n", numWritesThisTime,
            busBusyUntil - temp1, maxBankFreeAt() - temp2);

    // Update stats
    avgWrQLen = writeQueue.size();

    // turn the bus back around for reads again
    busBusyUntil += tWTR;
    stopReads = false;

    if (retryWrReq) {
        retryWrReq = false;
        port.sendRetry();
    }

    // if there is nothing left in any queue, signal a drain
    if (writeQueue.empty() && readQueue.empty() &&
        respQueue.empty () && drainManager) {
        drainManager->signalDrainDone();
        drainManager = NULL;
    }

    // Once you're done emptying the write queue, check if there's
    // anything in the read queue, and call schedule if required. The
    // retry above could already have caused it to be scheduled, so
    // first check
    if (!nextReqEvent.scheduled())
        schedule(nextReqEvent, busBusyUntil);
}


void
SimpleDRAM::triggerWrites()
{
    DPRINTF(DRAM, "Writes triggered at %lld\n", curTick());
    // Flag variable to stop any more read scheduling
    stopReads = true;

    writeStartTime = std::max(busBusyUntil, curTick()) + tWTR;

    DPRINTF(DRAM, "Writes scheduled at %lld\n", writeStartTime);

    assert(writeStartTime >= curTick());
    assert(!writeEvent.scheduled());
    schedule(writeEvent, writeStartTime);
}

void
SimpleDRAM::addToWriteQueue(PacketPtr pkt, unsigned int pktCount)
{
    // only add to the write queue here. whenever the request is
    // eventually done, set the readyTime, and call schedule()
    assert(pkt->isWrite());

    // if the request size is larger than burst size, the pkt is split into
    // multiple DRAM packets
    Addr addr = pkt->getAddr();
    for (int cnt = 0; cnt < pktCount; ++cnt) {
        unsigned size = std::min((addr | (burstSize - 1)) + 1,
                        pkt->getAddr() + pkt->getSize()) - addr;
        writePktSize[ceilLog2(size)]++;
        writeBursts++;

        // see if we can merge with an existing item in the write
        // queue and keep track of whether we have merged or not so we
        // can stop at that point and also avoid enqueueing a new
        // request
        bool merged = false;
        auto w = writeQueue.begin();

        while(!merged && w != writeQueue.end()) {
            // either of the two could be first, if they are the same
            // it does not matter which way we go
            if ((*w)->addr >= addr) {
                // the existing one starts after the new one, figure
                // out where the new one ends with respect to the
                // existing one
                if ((addr + size) >= ((*w)->addr + (*w)->size)) {
                    // check if the existing one is completely
                    // subsumed in the new one
                    DPRINTF(DRAM, "Merging write covering existing burst\n");
                    merged = true;
                    // update both the address and the size
                    (*w)->addr = addr;
                    (*w)->size = size;
                } else if ((addr + size) >= (*w)->addr &&
                           ((*w)->addr + (*w)->size - addr) <= burstSize) {
                    // the new one is just before or partially
                    // overlapping with the existing one, and together
                    // they fit within a burst
                    DPRINTF(DRAM, "Merging write before existing burst\n");
                    merged = true;
                    // the existing queue item needs to be adjusted with
                    // respect to both address and size
                    (*w)->addr = addr;
                    (*w)->size = (*w)->addr + (*w)->size - addr;
                }
            } else {
                // the new one starts after the current one, figure
                // out where the existing one ends with respect to the
                // new one
                if (((*w)->addr + (*w)->size) >= (addr + size)) {
                    // check if the new one is completely subsumed in the
                    // existing one
                    DPRINTF(DRAM, "Merging write into existing burst\n");
                    merged = true;
                    // no adjustments necessary
                } else if (((*w)->addr + (*w)->size) >= addr &&
                           (addr + size - (*w)->addr) <= burstSize) {
                    // the existing one is just before or partially
                    // overlapping with the new one, and together
                    // they fit within a burst
                    DPRINTF(DRAM, "Merging write after existing burst\n");
                    merged = true;
                    // the address is right, and only the size has
                    // to be adjusted
                    (*w)->size = addr + size - (*w)->addr;
                }
            }
            ++w;
        }

        // if the item was not merged we need to create a new write
        // and enqueue it
        if (!merged) {
            DRAMPacket* dram_pkt = decodeAddr(pkt, addr, size, false);

            assert(writeQueue.size() < writeBufferSize);
            wrQLenPdf[writeQueue.size()]++;

            DPRINTF(DRAM, "Adding to write queue\n");

            writeQueue.push_back(dram_pkt);

            // Update stats
            assert(dram_pkt->bankId < ranksPerChannel * banksPerRank);
            perBankWrReqs[dram_pkt->bankId]++;

            avgWrQLen = writeQueue.size();
        }

        bytesConsumedWr += size;
        bytesWritten += burstSize;

        // Starting address of next dram pkt (aligend to burstSize boundary)
        addr = (addr | (burstSize - 1)) + 1;
    }

    // we do not wait for the writes to be send to the actual memory,
    // but instead take responsibility for the consistency here and
    // snoop the write queue for any upcoming reads
    // @todo, if a pkt size is larger than burst size, we might need a
    // different front end latency
    accessAndRespond(pkt, frontendLatency);

    // If your write buffer is starting to fill up, drain it!
    if (writeQueue.size() > writeThreshold && !stopReads){
        triggerWrites();
    }
}

void
SimpleDRAM::printParams() const
{
    // Sanity check print of important parameters
    DPRINTF(DRAM,
            "Memory controller %s physical organization\n"      \
            "Number of devices per rank   %d\n"                 \
            "Device bus width (in bits)   %d\n"                 \
            "DRAM data bus burst          %d\n"                 \
            "Row buffer size              %d\n"                 \
            "Columns per row buffer       %d\n"                 \
            "Rows    per bank             %d\n"                 \
            "Banks   per rank             %d\n"                 \
            "Ranks   per channel          %d\n"                 \
            "Total mem capacity           %u\n",
            name(), devicesPerRank, deviceBusWidth, burstSize, rowBufferSize,
            columnsPerRowBuffer, rowsPerBank, banksPerRank, ranksPerChannel,
            rowBufferSize * rowsPerBank * banksPerRank * ranksPerChannel);

    string scheduler =  memSchedPolicy == Enums::fcfs ? "FCFS" : "FR-FCFS";
    string address_mapping = addrMapping == Enums::RaBaChCo ? "RaBaChCo" :
        (addrMapping == Enums::RaBaCoCh ? "RaBaCoCh" : "CoRaBaCh");
    string page_policy = pageMgmt == Enums::open ? "OPEN" : "CLOSE";

    DPRINTF(DRAM,
            "Memory controller %s characteristics\n"    \
            "Read buffer size     %d\n"                 \
            "Write buffer size    %d\n"                 \
            "Write buffer thresh  %d\n"                 \
            "Scheduler            %s\n"                 \
            "Address mapping      %s\n"                 \
            "Page policy          %s\n",
            name(), readBufferSize, writeBufferSize, writeThreshold,
            scheduler, address_mapping, page_policy);

    DPRINTF(DRAM, "Memory controller %s timing specs\n" \
            "tRCD      %d ticks\n"                        \
            "tCL       %d ticks\n"                        \
            "tRP       %d ticks\n"                        \
            "tBURST    %d ticks\n"                        \
            "tRFC      %d ticks\n"                        \
            "tREFI     %d ticks\n"                        \
            "tWTR      %d ticks\n"                        \
            "tXAW (%d) %d ticks\n",
            name(), tRCD, tCL, tRP, tBURST, tRFC, tREFI, tWTR,
            activationLimit, tXAW);
}

void
SimpleDRAM::printQs() const {
    DPRINTF(DRAM, "===READ QUEUE===\n\n");
    for (auto i = readQueue.begin() ;  i != readQueue.end() ; ++i) {
        DPRINTF(DRAM, "Read %lu\n", (*i)->addr);
    }
    DPRINTF(DRAM, "\n===RESP QUEUE===\n\n");
    for (auto i = respQueue.begin() ;  i != respQueue.end() ; ++i) {
        DPRINTF(DRAM, "Response %lu\n", (*i)->addr);
    }
    DPRINTF(DRAM, "\n===WRITE QUEUE===\n\n");
    for (auto i = writeQueue.begin() ;  i != writeQueue.end() ; ++i) {
        DPRINTF(DRAM, "Write %lu\n", (*i)->addr);
    }
}

bool
SimpleDRAM::recvTimingReq(PacketPtr pkt)
{
    /// @todo temporary hack to deal with memory corruption issues until
    /// 4-phase transactions are complete
    for (int x = 0; x < pendingDelete.size(); x++)
        delete pendingDelete[x];
    pendingDelete.clear();

    // This is where we enter from the outside world
    DPRINTF(DRAM, "recvTimingReq: request %s addr %lld size %d\n",
            pkt->cmdString(), pkt->getAddr(), pkt->getSize());

    // simply drop inhibited packets for now
    if (pkt->memInhibitAsserted()) {
        DPRINTF(DRAM,"Inhibited packet -- Dropping it now\n");
        pendingDelete.push_back(pkt);
        return true;
    }

   // Every million accesses, print the state of the queues
   if (numReqs % 1000000 == 0)
       printQs();

    // Calc avg gap between requests
    if (prevArrival != 0) {
        totGap += curTick() - prevArrival;
    }
    prevArrival = curTick();


    // Find out how many dram packets a pkt translates to
    // If the burst size is equal or larger than the pkt size, then a pkt
    // translates to only one dram packet. Otherwise, a pkt translates to
    // multiple dram packets
    unsigned size = pkt->getSize();
    unsigned offset = pkt->getAddr() & (burstSize - 1);
    unsigned int dram_pkt_count = divCeil(offset + size, burstSize);

    // check local buffers and do not accept if full
    if (pkt->isRead()) {
        assert(size != 0);
        if (readQueueFull(dram_pkt_count)) {
            DPRINTF(DRAM, "Read queue full, not accepting\n");
            // remember that we have to retry this port
            retryRdReq = true;
            numRdRetry++;
            return false;
        } else {
            addToReadQueue(pkt, dram_pkt_count);
            readReqs++;
            numReqs++;
        }
    } else if (pkt->isWrite()) {
        assert(size != 0);
        if (writeQueueFull(dram_pkt_count)) {
            DPRINTF(DRAM, "Write queue full, not accepting\n");
            // remember that we have to retry this port
            retryWrReq = true;
            numWrRetry++;
            return false;
        } else {
            addToWriteQueue(pkt, dram_pkt_count);
            writeReqs++;
            numReqs++;
        }
    } else {
        DPRINTF(DRAM,"Neither read nor write, ignore timing\n");
        neitherReadNorWrite++;
        accessAndRespond(pkt, 1);
    }

    retryRdReq = false;
    retryWrReq = false;
    return true;
}

void
SimpleDRAM::processRespondEvent()
{
    DPRINTF(DRAM,
            "processRespondEvent(): Some req has reached its readyTime\n");

    DRAMPacket* dram_pkt = respQueue.front();

    // Actually responds to the requestor
    bytesConsumedRd += dram_pkt->size;
    bytesRead += burstSize;
    if (dram_pkt->burstHelper) {
        // it is a split packet
        dram_pkt->burstHelper->burstsServiced++;
        if (dram_pkt->burstHelper->burstsServiced ==
                                  dram_pkt->burstHelper->burstCount) {
            // we have now serviced all children packets of a system packet
            // so we can now respond to the requester
            // @todo we probably want to have a different front end and back
            // end latency for split packets
            accessAndRespond(dram_pkt->pkt, frontendLatency + backendLatency);
            delete dram_pkt->burstHelper;
            dram_pkt->burstHelper = NULL;
        }
    } else {
        // it is not a split packet
        accessAndRespond(dram_pkt->pkt, frontendLatency + backendLatency);
    }

    delete respQueue.front();
    respQueue.pop_front();

    // Update stats
    avgRdQLen = readQueue.size() + respQueue.size();

    if (!respQueue.empty()) {
        assert(respQueue.front()->readyTime >= curTick());
        assert(!respondEvent.scheduled());
        schedule(respondEvent, respQueue.front()->readyTime);
    } else {
        // if there is nothing left in any queue, signal a drain
        if (writeQueue.empty() && readQueue.empty() &&
            drainManager) {
            drainManager->signalDrainDone();
            drainManager = NULL;
        }
    }

    // We have made a location in the queue available at this point,
    // so if there is a read that was forced to wait, retry now
    if (retryRdReq) {
        retryRdReq = false;
        port.sendRetry();
    }
}

void
SimpleDRAM::chooseNextWrite()
{
    // This method does the arbitration between write requests. The
    // chosen packet is simply moved to the head of the write
    // queue. The other methods know that this is the place to
    // look. For example, with FCFS, this method does nothing
    assert(!writeQueue.empty());

    if (writeQueue.size() == 1) {
        DPRINTF(DRAM, "Single write request, nothing to do\n");
        return;
    }

    if (memSchedPolicy == Enums::fcfs) {
        // Do nothing, since the correct request is already head
    } else if (memSchedPolicy == Enums::frfcfs) {
        // Only determine bank availability when needed
        uint64_t earliest_banks = 0;

        auto i = writeQueue.begin();
        bool foundRowHit = false;
        while (!foundRowHit && i != writeQueue.end()) {
            DRAMPacket* dram_pkt = *i;
            const Bank& bank = dram_pkt->bankRef;
            if (bank.openRow == dram_pkt->row) {
                DPRINTF(DRAM, "Write row buffer hit\n");
                writeQueue.erase(i);
                writeQueue.push_front(dram_pkt);
                foundRowHit = true;
            } else {
                // No row hit, go for first ready
                if (earliest_banks == 0)
                    earliest_banks = minBankFreeAt(writeQueue);

                // Bank is ready or is one of the first available bank
                if (bank.freeAt <= curTick() ||
                    bits(earliest_banks, dram_pkt->bankId, dram_pkt->bankId)) {
                    writeQueue.erase(i);
                    writeQueue.push_front(dram_pkt);
                    break;
                }
            }
            ++i;
        }
    } else
        panic("No scheduling policy chosen\n");

    DPRINTF(DRAM, "Selected next write request\n");
}

bool
SimpleDRAM::chooseNextRead()
{
    // This method does the arbitration between read requests. The
    // chosen packet is simply moved to the head of the queue. The
    // other methods know that this is the place to look. For example,
    // with FCFS, this method does nothing
    if (readQueue.empty()) {
        DPRINTF(DRAM, "No read request to select\n");
        return false;
    }

    // If there is only one request then there is nothing left to do
    if (readQueue.size() == 1)
        return true;

    if (memSchedPolicy == Enums::fcfs) {
        // Do nothing, since the request to serve is already the first
        // one in the read queue
    } else if (memSchedPolicy == Enums::frfcfs) {
        // Only determine this when needed
        uint64_t earliest_banks = 0;

        for (auto i = readQueue.begin(); i != readQueue.end() ; ++i) {
            DRAMPacket* dram_pkt = *i;
            const Bank& bank = dram_pkt->bankRef;
            // Check if it is a row hit
            if (bank.openRow == dram_pkt->row) {
                DPRINTF(DRAM, "Row buffer hit\n");
                readQueue.erase(i);
                readQueue.push_front(dram_pkt);
                break;
            } else {
                // No row hit, go for first ready
                if (earliest_banks == 0)
                    earliest_banks = minBankFreeAt(readQueue);

                // Bank is ready or is the first available bank
                if (bank.freeAt <= curTick() ||
                    bits(earliest_banks, dram_pkt->bankId, dram_pkt->bankId)) {
                    readQueue.erase(i);
                    readQueue.push_front(dram_pkt);
                    break;
                }
            }
        }
    } else
        panic("No scheduling policy chosen!\n");

    DPRINTF(DRAM, "Selected next read request\n");
    return true;
}

void
SimpleDRAM::accessAndRespond(PacketPtr pkt, Tick static_latency)
{
    DPRINTF(DRAM, "Responding to Address %lld.. ",pkt->getAddr());

    bool needsResponse = pkt->needsResponse();
    // do the actual memory access which also turns the packet into a
    // response
    access(pkt);

    // turn packet around to go back to requester if response expected
    if (needsResponse) {
        // access already turned the packet into a response
        assert(pkt->isResponse());

        // @todo someone should pay for this
        pkt->busFirstWordDelay = pkt->busLastWordDelay = 0;

        // queue the packet in the response queue to be sent out after
        // the static latency has passed
        port.schedTimingResp(pkt, curTick() + static_latency);
    } else {
        // @todo the packet is going to be deleted, and the DRAMPacket
        // is still having a pointer to it
        pendingDelete.push_back(pkt);
    }

    DPRINTF(DRAM, "Done\n");

    return;
}

pair<Tick, Tick>
SimpleDRAM::estimateLatency(DRAMPacket* dram_pkt, Tick inTime)
{
    // If a request reaches a bank at tick 'inTime', how much time
    // *after* that does it take to finish the request, depending
    // on bank status and page open policy. Note that this method
    // considers only the time taken for the actual read or write
    // to complete, NOT any additional time thereafter for tRAS or
    // tRP.
    Tick accLat = 0;
    Tick bankLat = 0;
    rowHitFlag = false;

    const Bank& bank = dram_pkt->bankRef;
    if (pageMgmt == Enums::open) { // open-page policy
        if (bank.openRow == dram_pkt->row) {
            // When we have a row-buffer hit,
            // we don't care about tRAS having expired or not,
            // but do care about bank being free for access
            rowHitFlag = true;

            // When a series of requests arrive to the same row,
            // DDR systems are capable of streaming data continuously
            // at maximum bandwidth (subject to tCCD). Here, we approximate
            // this condition, and assume that if whenever a bank is already
            // busy and a new request comes in, it can be completed with no
            // penalty beyond waiting for the existing read to complete.
            if (bank.freeAt > inTime) {
                accLat += bank.freeAt - inTime;
                bankLat += 0;
            } else {
               // CAS latency only
               accLat += tCL;
               bankLat += tCL;
            }

        } else {
            // Row-buffer miss, need to close existing row
            // once tRAS has expired, then open the new one,
            // then add cas latency.
            Tick freeTime = std::max(bank.tRASDoneAt, bank.freeAt);

            if (freeTime > inTime)
               accLat += freeTime - inTime;

            accLat += tRP + tRCD + tCL;
            bankLat += tRP + tRCD + tCL;
        }
    } else if (pageMgmt == Enums::close) {
        // With a close page policy, no notion of
        // bank.tRASDoneAt
        if (bank.freeAt > inTime)
            accLat += bank.freeAt - inTime;

        // page already closed, simply open the row, and
        // add cas latency
        accLat += tRCD + tCL;
        bankLat += tRCD + tCL;
    } else
        panic("No page management policy chosen\n");

    DPRINTF(DRAM, "Returning < %lld, %lld > from estimateLatency()\n",
            bankLat, accLat);

    return make_pair(bankLat, accLat);
}

void
SimpleDRAM::processNextReqEvent()
{
    scheduleNextReq();
}

void
SimpleDRAM::recordActivate(Tick act_tick)
{
    assert(actTicks.size() == activationLimit);

    DPRINTF(DRAM, "Activate at tick %d\n", act_tick);

    // if the activation limit is disabled then we are done
    if (actTicks.empty())
        return;

    // sanity check
    if (actTicks.back() && (act_tick - actTicks.back()) < tXAW) {
        // @todo For now, stick with a warning
        warn("Got %d activates in window %d (%d - %d) which is smaller "
             "than %d\n", activationLimit, act_tick - actTicks.back(),
             act_tick, actTicks.back(), tXAW);
    }

    // shift the times used for the book keeping, the last element
    // (highest index) is the oldest one and hence the lowest value
    actTicks.pop_back();

    // record an new activation (in the future)
    actTicks.push_front(act_tick);

    // cannot activate more than X times in time window tXAW, push the
    // next one (the X + 1'st activate) to be tXAW away from the
    // oldest in our window of X
    if (actTicks.back() && (act_tick - actTicks.back()) < tXAW) {
        DPRINTF(DRAM, "Enforcing tXAW with X = %d, next activate no earlier "
                "than %d\n", activationLimit, actTicks.back() + tXAW);
        for(int i = 0; i < ranksPerChannel; i++)
            for(int j = 0; j < banksPerRank; j++)
                // next activate must not happen before end of window
                banks[i][j].freeAt = std::max(banks[i][j].freeAt,
                                              actTicks.back() + tXAW);
    }
}

void
SimpleDRAM::doDRAMAccess(DRAMPacket* dram_pkt)
{

    DPRINTF(DRAM, "Timing access to addr %lld, rank/bank/row %d %d %d\n",
            dram_pkt->addr, dram_pkt->rank, dram_pkt->bank, dram_pkt->row);

    // estimate the bank and access latency
    pair<Tick, Tick> lat = estimateLatency(dram_pkt, curTick());
    Tick bankLat = lat.first;
    Tick accessLat = lat.second;
    Tick actTick;

    // This request was woken up at this time based on a prior call
    // to estimateLatency(). However, between then and now, both the
    // accessLatency and/or busBusyUntil may have changed. We need
    // to correct for that.

    Tick addDelay = (curTick() + accessLat < busBusyUntil) ?
        busBusyUntil - (curTick() + accessLat) : 0;

    Bank& bank = dram_pkt->bankRef;

    // Update bank state
    if (pageMgmt == Enums::open) {
        bank.openRow = dram_pkt->row;
        bank.freeAt = curTick() + addDelay + accessLat;
        bank.bytesAccessed += burstSize;

        // If you activated a new row do to this access, the next access
        // will have to respect tRAS for this bank.
        if (!rowHitFlag) {
            // any waiting for banks account for in freeAt
            actTick = bank.freeAt - tCL - tRCD;
            bank.tRASDoneAt = actTick + tRAS;
            recordActivate(actTick);

            // sample the number of bytes accessed and reset it as
            // we are now closing this row
            bytesPerActivate.sample(bank.bytesAccessed);
            bank.bytesAccessed = 0;
        }
    } else if (pageMgmt == Enums::close) {
        actTick = curTick() + addDelay + accessLat - tRCD - tCL;
        recordActivate(actTick);

        // If the DRAM has a very quick tRAS, bank can be made free
        // after consecutive tCL,tRCD,tRP times. In general, however,
        // an additional wait is required to respect tRAS.
        bank.freeAt = std::max(actTick + tRAS + tRP,
                actTick + tRCD + tCL + tRP);

        DPRINTF(DRAM,"doDRAMAccess::bank.freeAt is %lld\n",bank.freeAt);
        bytesPerActivate.sample(burstSize);
    } else
        panic("No page management policy chosen\n");

    // Update request parameters
    dram_pkt->readyTime = curTick() + addDelay + accessLat + tBURST;


    DPRINTF(DRAM, "Req %lld: curtick is %lld accessLat is %d " \
                  "readytime is %lld busbusyuntil is %lld. " \
                  "Scheduling at readyTime\n", dram_pkt->addr,
                   curTick(), accessLat, dram_pkt->readyTime, busBusyUntil);

    // Make sure requests are not overlapping on the databus
    assert (dram_pkt->readyTime - busBusyUntil >= tBURST);

    // Update bus state
    busBusyUntil = dram_pkt->readyTime;

    DPRINTF(DRAM,"Access time is %lld\n",
            dram_pkt->readyTime - dram_pkt->entryTime);

    if (rowHitFlag) {
        if(dram_pkt->isRead)
            readRowHits++;
         else
            writeRowHits++;
    }

    // At this point, commonality between reads and writes ends.
    // For writes, we are done since we long ago responded to the
    // requestor. We also don't care about stats for writes. For
    // reads, we still need to figure out respoding to the requestor,
    // and capture stats.

    if (!dram_pkt->isRead) {
        return;
    }

    // Update stats
    totMemAccLat += dram_pkt->readyTime - dram_pkt->entryTime;
    totBankLat += bankLat;
    totBusLat += tBURST;
    totQLat += dram_pkt->readyTime - dram_pkt->entryTime - bankLat - tBURST;


    // At this point we're done dealing with the request
    // It will be moved to a separate response queue with a
    // correct readyTime, and eventually be sent back at that
    //time
    moveToRespQ();

    // The absolute soonest you have to start thinking about the
    // next request is the longest access time that can occur before
    // busBusyUntil. Assuming you need to precharge,
    // open a new row, and access, it is tRP + tRCD + tCL

    Tick newTime = (busBusyUntil > tRP + tRCD + tCL ) ?
                   std::max(busBusyUntil - (tRP + tRCD + tCL) , curTick()) :
                   curTick();

    if (!nextReqEvent.scheduled() && !stopReads){
        schedule(nextReqEvent, newTime);
    } else {
        if (newTime < nextReqEvent.when())
            reschedule(nextReqEvent, newTime);
    }


}

void
SimpleDRAM::moveToRespQ()
{
    // Remove from read queue
    DRAMPacket* dram_pkt = readQueue.front();
    readQueue.pop_front();

    // sanity check
    assert(dram_pkt->size <= burstSize);

    // Insert into response queue sorted by readyTime
    // It will be sent back to the requestor at its
    // readyTime
    if (respQueue.empty()) {
        respQueue.push_front(dram_pkt);
        assert(!respondEvent.scheduled());
        assert(dram_pkt->readyTime >= curTick());
        schedule(respondEvent, dram_pkt->readyTime);
    } else {
        bool done = false;
        auto i = respQueue.begin();
        while (!done && i != respQueue.end()) {
            if ((*i)->readyTime > dram_pkt->readyTime) {
                respQueue.insert(i, dram_pkt);
                done = true;
            }
            ++i;
        }

        if (!done)
            respQueue.push_back(dram_pkt);

        assert(respondEvent.scheduled());

        if (respQueue.front()->readyTime < respondEvent.when()) {
            assert(respQueue.front()->readyTime >= curTick());
            reschedule(respondEvent, respQueue.front()->readyTime);
        }
    }
}

void
SimpleDRAM::scheduleNextReq()
{
    DPRINTF(DRAM, "Reached scheduleNextReq()\n");

    // Figure out which read request goes next, and move it to the
    // front of the read queue
    if (!chooseNextRead()) {
        // In the case there is no read request to go next, see if we
        // are asked to drain, and if so trigger writes, this also
        // ensures that if we hit the write limit we will do this
        // multiple times until we are completely drained
        if (drainManager && !writeQueue.empty() && !writeEvent.scheduled())
            triggerWrites();
    } else {
        doDRAMAccess(readQueue.front());
    }
}

Tick
SimpleDRAM::maxBankFreeAt() const
{
    Tick banksFree = 0;

    for(int i = 0; i < ranksPerChannel; i++)
        for(int j = 0; j < banksPerRank; j++)
            banksFree = std::max(banks[i][j].freeAt, banksFree);

    return banksFree;
}

uint64_t
SimpleDRAM::minBankFreeAt(const deque<DRAMPacket*>& queue) const
{
    uint64_t bank_mask = 0;
    Tick freeAt = MaxTick;

    // detemrine if we have queued transactions targetting the
    // bank in question
    vector<bool> got_waiting(ranksPerChannel * banksPerRank, false);
    for (auto p = queue.begin(); p != queue.end(); ++p) {
        got_waiting[(*p)->bankId] = true;
    }

    for (int i = 0; i < ranksPerChannel; i++) {
        for (int j = 0; j < banksPerRank; j++) {
            // if we have waiting requests for the bank, and it is
            // amongst the first available, update the mask
            if (got_waiting[i * banksPerRank + j] &&
                banks[i][j].freeAt <= freeAt) {
                // reset bank mask if new minimum is found
                if (banks[i][j].freeAt < freeAt)
                    bank_mask = 0;
                // set the bit corresponding to the available bank
                uint8_t bit_index = i * ranksPerChannel + j;
                replaceBits(bank_mask, bit_index, bit_index, 1);
                freeAt = banks[i][j].freeAt;
            }
        }
    }
    return bank_mask;
}

void
SimpleDRAM::processRefreshEvent()
{
    DPRINTF(DRAM, "Refreshing at tick %ld\n", curTick());

    Tick banksFree = std::max(curTick(), maxBankFreeAt()) + tRFC;

    for(int i = 0; i < ranksPerChannel; i++)
        for(int j = 0; j < banksPerRank; j++)
            banks[i][j].freeAt = banksFree;

    schedule(refreshEvent, curTick() + tREFI);
}

void
SimpleDRAM::regStats()
{
    using namespace Stats;

    AbstractMemory::regStats();

    readReqs
        .name(name() + ".readReqs")
        .desc("Total number of read requests accepted by DRAM controller");

    writeReqs
        .name(name() + ".writeReqs")
        .desc("Total number of write requests accepted by DRAM controller");

    readBursts
        .name(name() + ".readBursts")
        .desc("Total number of DRAM read bursts. "
              "Each DRAM read request translates to either one or multiple "
              "DRAM read bursts");

    writeBursts
        .name(name() + ".writeBursts")
        .desc("Total number of DRAM write bursts. "
              "Each DRAM write request translates to either one or multiple "
              "DRAM write bursts");

    servicedByWrQ
        .name(name() + ".servicedByWrQ")
        .desc("Number of DRAM read bursts serviced by write Q");

    neitherReadNorWrite
        .name(name() + ".neitherReadNorWrite")
        .desc("Reqs where no action is needed");

    perBankRdReqs
        .init(banksPerRank * ranksPerChannel)
        .name(name() + ".perBankRdReqs")
        .desc("Track reads on a per bank basis");

    perBankWrReqs
        .init(banksPerRank * ranksPerChannel)
        .name(name() + ".perBankWrReqs")
        .desc("Track writes on a per bank basis");

    avgRdQLen
        .name(name() + ".avgRdQLen")
        .desc("Average read queue length over time")
        .precision(2);

    avgWrQLen
        .name(name() + ".avgWrQLen")
        .desc("Average write queue length over time")
        .precision(2);

    totQLat
        .name(name() + ".totQLat")
        .desc("Total cycles spent in queuing delays");

    totBankLat
        .name(name() + ".totBankLat")
        .desc("Total cycles spent in bank access");

    totBusLat
        .name(name() + ".totBusLat")
        .desc("Total cycles spent in databus access");

    totMemAccLat
        .name(name() + ".totMemAccLat")
        .desc("Sum of mem lat for all requests");

    avgQLat
        .name(name() + ".avgQLat")
        .desc("Average queueing delay per request")
        .precision(2);

    avgQLat = totQLat / (readBursts - servicedByWrQ);

    avgBankLat
        .name(name() + ".avgBankLat")
        .desc("Average bank access latency per request")
        .precision(2);

    avgBankLat = totBankLat / (readBursts - servicedByWrQ);

    avgBusLat
        .name(name() + ".avgBusLat")
        .desc("Average bus latency per request")
        .precision(2);

    avgBusLat = totBusLat / (readBursts - servicedByWrQ);

    avgMemAccLat
        .name(name() + ".avgMemAccLat")
        .desc("Average memory access latency")
        .precision(2);

    avgMemAccLat = totMemAccLat / (readBursts - servicedByWrQ);

    numRdRetry
        .name(name() + ".numRdRetry")
        .desc("Number of times rd buffer was full causing retry");

    numWrRetry
        .name(name() + ".numWrRetry")
        .desc("Number of times wr buffer was full causing retry");

    readRowHits
        .name(name() + ".readRowHits")
        .desc("Number of row buffer hits during reads");

    writeRowHits
        .name(name() + ".writeRowHits")
        .desc("Number of row buffer hits during writes");

    readRowHitRate
        .name(name() + ".readRowHitRate")
        .desc("Row buffer hit rate for reads")
        .precision(2);

    readRowHitRate = (readRowHits / (readBursts - servicedByWrQ)) * 100;

    writeRowHitRate
        .name(name() + ".writeRowHitRate")
        .desc("Row buffer hit rate for writes")
        .precision(2);

    writeRowHitRate = (writeRowHits / writeBursts) * 100;

    readPktSize
        .init(ceilLog2(burstSize) + 1)
        .name(name() + ".readPktSize")
        .desc("Categorize read packet sizes");

     writePktSize
        .init(ceilLog2(burstSize) + 1)
        .name(name() + ".writePktSize")
        .desc("Categorize write packet sizes");

     rdQLenPdf
        .init(readBufferSize)
        .name(name() + ".rdQLenPdf")
        .desc("What read queue length does an incoming req see");

     wrQLenPdf
        .init(writeBufferSize)
        .name(name() + ".wrQLenPdf")
        .desc("What write queue length does an incoming req see");

     bytesPerActivate
         .init(rowBufferSize)
         .name(name() + ".bytesPerActivate")
         .desc("Bytes accessed per row activation")
         .flags(nozero);

    bytesRead
        .name(name() + ".bytesRead")
        .desc("Total number of bytes read from memory");

    bytesWritten
        .name(name() + ".bytesWritten")
        .desc("Total number of bytes written to memory");

    bytesConsumedRd
        .name(name() + ".bytesConsumedRd")
        .desc("bytesRead derated as per pkt->getSize()");

    bytesConsumedWr
        .name(name() + ".bytesConsumedWr")
        .desc("bytesWritten derated as per pkt->getSize()");

    avgRdBW
        .name(name() + ".avgRdBW")
        .desc("Average achieved read bandwidth in MB/s")
        .precision(2);

    avgRdBW = (bytesRead / 1000000) / simSeconds;

    avgWrBW
        .name(name() + ".avgWrBW")
        .desc("Average achieved write bandwidth in MB/s")
        .precision(2);

    avgWrBW = (bytesWritten / 1000000) / simSeconds;

    avgConsumedRdBW
        .name(name() + ".avgConsumedRdBW")
        .desc("Average consumed read bandwidth in MB/s")
        .precision(2);

    avgConsumedRdBW = (bytesConsumedRd / 1000000) / simSeconds;

    avgConsumedWrBW
        .name(name() + ".avgConsumedWrBW")
        .desc("Average consumed write bandwidth in MB/s")
        .precision(2);

    avgConsumedWrBW = (bytesConsumedWr / 1000000) / simSeconds;

    peakBW
        .name(name() + ".peakBW")
        .desc("Theoretical peak bandwidth in MB/s")
        .precision(2);

    peakBW = (SimClock::Frequency / tBURST) * burstSize / 1000000;

    busUtil
        .name(name() + ".busUtil")
        .desc("Data bus utilization in percentage")
        .precision(2);

    busUtil = (avgRdBW + avgWrBW) / peakBW * 100;

    totGap
        .name(name() + ".totGap")
        .desc("Total gap between requests");

    avgGap
        .name(name() + ".avgGap")
        .desc("Average gap between requests")
        .precision(2);

    avgGap = totGap / (readReqs + writeReqs);
}

void
SimpleDRAM::recvFunctional(PacketPtr pkt)
{
    // rely on the abstract memory
    functionalAccess(pkt);
}

BaseSlavePort&
SimpleDRAM::getSlavePort(const string &if_name, PortID idx)
{
    if (if_name != "port") {
        return MemObject::getSlavePort(if_name, idx);
    } else {
        return port;
    }
}

unsigned int
SimpleDRAM::drain(DrainManager *dm)
{
    unsigned int count = port.drain(dm);

    // if there is anything in any of our internal queues, keep track
    // of that as well
    if (!(writeQueue.empty() && readQueue.empty() &&
          respQueue.empty())) {
        DPRINTF(Drain, "DRAM controller not drained, write: %d, read: %d,"
                " resp: %d\n", writeQueue.size(), readQueue.size(),
                respQueue.size());
        ++count;
        drainManager = dm;
        // the only part that is not drained automatically over time
        // is the write queue, thus trigger writes if there are any
        // waiting and no reads waiting, otherwise wait until the
        // reads are done
        if (readQueue.empty() && !writeQueue.empty() &&
            !writeEvent.scheduled())
            triggerWrites();
    }

    if (count)
        setDrainState(Drainable::Draining);
    else
        setDrainState(Drainable::Drained);
    return count;
}

SimpleDRAM::MemoryPort::MemoryPort(const std::string& name, SimpleDRAM& _memory)
    : QueuedSlavePort(name, &_memory, queue), queue(_memory, *this),
      memory(_memory)
{ }

AddrRangeList
SimpleDRAM::MemoryPort::getAddrRanges() const
{
    AddrRangeList ranges;
    ranges.push_back(memory.getAddrRange());
    return ranges;
}

void
SimpleDRAM::MemoryPort::recvFunctional(PacketPtr pkt)
{
    pkt->pushLabel(memory.name());

    if (!queue.checkFunctional(pkt)) {
        // Default implementation of SimpleTimingPort::recvFunctional()
        // calls recvAtomic() and throws away the latency; we can save a
        // little here by just not calculating the latency.
        memory.recvFunctional(pkt);
    }

    pkt->popLabel();
}

Tick
SimpleDRAM::MemoryPort::recvAtomic(PacketPtr pkt)
{
    return memory.recvAtomic(pkt);
}

bool
SimpleDRAM::MemoryPort::recvTimingReq(PacketPtr pkt)
{
    // pass it to the memory controller
    return memory.recvTimingReq(pkt);
}

SimpleDRAM*
SimpleDRAMParams::create()
{
    return new SimpleDRAM(this);
}