src/mem/bus.cc

   1 /*
   2  * Copyright (c) 2006 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Ali Saidi
  29  */
  30
  31 /**
  32  * @file
  33  * Definition of a bus object.
  34  */
  35
  36 #include <algorithm>
  37 #include <limits>
  38
  39 #include "base/misc.hh"
  40 #include "base/trace.hh"
  41 #include "mem/bus.hh"
  42
  43 Port *
  44 Bus::getPort(const std::string &if_name, int idx)
  45 {
  46     if (if_name == "default") {
  47         if (defaultPort == NULL) {
  48             defaultPort = new BusPort(csprintf("%s-default",name()), this,
  49                                       defaultId);
  50             cachedBlockSizeValid = false;
  51             return defaultPort;
  52         } else
  53             fatal("Default port already set\n");
  54     }
  55     int id;
  56     if (if_name == "functional") {
  57         if (!funcPort) {
  58             id = maxId++;
  59             funcPort = new BusPort(csprintf("%s-p%d-func", name(), id), this, id);
  60             funcPortId = id;
  61             interfaces[id] = funcPort;
  62         }
  63         return funcPort;
  64     }
  65
  66     // if_name ignored?  forced to be empty?
  67     id = maxId++;
  68     assert(maxId < std::numeric_limits<typeof(maxId)>::max());
  69     BusPort *bp = new BusPort(csprintf("%s-p%d", name(), id), this, id);
  70     interfaces[id] = bp;
  71     cachedBlockSizeValid = false;
  72     return bp;
  73 }
  74
  75 void
  76 Bus::deletePortRefs(Port *p)
  77 {
  78
  79     BusPort *bp =  dynamic_cast<BusPort*>(p);
  80     if (bp == NULL)
  81         panic("Couldn't convert Port* to BusPort*\n");
  82     // If this is our one functional port
  83     if (funcPort == bp)
  84         return;
  85     interfaces.erase(bp->getId());
  86     clearBusCache();
  87     delete bp;
  88 }
  89
  90 /** Get the ranges of anyone other buses that we are connected to. */
  91 void
  92 Bus::init()
  93 {
  94     m5::hash_map<short,BusPort*>::iterator intIter;
  95
  96     for (intIter = interfaces.begin(); intIter != interfaces.end(); intIter++)
  97         intIter->second->sendStatusChange(Port::RangeChange);
  98 }
  99
 100 Bus::BusFreeEvent::BusFreeEvent(Bus *_bus) : Event(&mainEventQueue), bus(_bus)
 101 {}
 102
 103 void Bus::BusFreeEvent::process()
 104 {
 105     bus->recvRetry(-1);
 106 }
 107
 108 const char * Bus::BusFreeEvent::description()
 109 {
 110     return "bus became available";
 111 }
 112
 113 void Bus::occupyBus(PacketPtr pkt)
 114 {
 115     //Bring tickNextIdle up to the present tick
 116     //There is some potential ambiguity where a cycle starts, which might make
 117     //a difference when devices are acting right around a cycle boundary. Using
 118     //a < allows things which happen exactly on a cycle boundary to take up
 119     //only the following cycle. Anything that happens later will have to "wait"
 120     //for the end of that cycle, and then start using the bus after that.
 121     if (tickNextIdle < curTick) {
 122         tickNextIdle = curTick;
 123         if (tickNextIdle % clock != 0)
 124             tickNextIdle = curTick - (curTick % clock) + clock;
 125     }
 126
 127     // The packet will be sent. Figure out how long it occupies the bus, and
 128     // how much of that time is for the first "word", aka bus width.
 129     int numCycles = 0;
 130     // Requests need one cycle to send an address
 131     if (pkt->isRequest())
 132         numCycles++;
 133     else if (pkt->isResponse() || pkt->hasData()) {
 134         // If a packet has data, it needs ceil(size/width) cycles to send it
 135         // We're using the "adding instead of dividing" trick again here
 136         if (pkt->hasData()) {
 137             int dataSize = pkt->getSize();
 138             numCycles += dataSize/width;
 139             if (dataSize % width)
 140                 numCycles++;
 141         } else {
 142             // If the packet didn't have data, it must have been a response.
 143             // Those use the bus for one cycle to send their data.
 144             numCycles++;
 145         }
 146     }
 147
 148     // The first word will be delivered after the current tick, the delivery
 149     // of the address if any, and one bus cycle to deliver the data
 150     pkt->firstWordTime = tickNextIdle + (pkt->isRequest() ? clock : 0) + clock;
 151
 152     //Advance it numCycles bus cycles.
 153     //XXX Should this use the repeated addition trick as well?
 154     tickNextIdle += (numCycles * clock);
 155     if (!busIdle.scheduled()) {
 156         busIdle.schedule(tickNextIdle);
 157     } else {
 158         busIdle.reschedule(tickNextIdle);
 159     }
 160     DPRINTF(Bus, "The bus is now occupied from tick %d to %d\n",
 161             curTick, tickNextIdle);
 162
 163     // The bus will become idle once the current packet is delivered.
 164     pkt->finishTime = tickNextIdle;
 165 }
 166
 167 /** Function called by the port when the bus is receiving a Timing
 168  * transaction.*/
 169 bool
 170 Bus::recvTiming(PacketPtr pkt)
 171 {
 172     short src = pkt->getSrc();
 173
 174     BusPort *src_port;
 175     if (src == defaultId)
 176         src_port = defaultPort;
 177     else {
 178         src_port = checkBusCache(src);
 179         if (src_port == NULL) {
 180             src_port = interfaces[src];
 181             updateBusCache(src, src_port);
 182         }
 183     }
 184
 185     // If the bus is busy, or other devices are in line ahead of the current
 186     // one, put this device on the retry list.
 187     if (!pkt->isExpressSnoop() &&
 188         (tickNextIdle > curTick ||
 189          (retryList.size() && (!inRetry || src_port != retryList.front()))))
 190     {
 191         addToRetryList(src_port);
 192         DPRINTF(Bus, "recvTiming: src %d dst %d %s 0x%x BUSY\n",
 193                 src, pkt->getDest(), pkt->cmdString(), pkt->getAddr());
 194         return false;
 195     }
 196
 197     DPRINTF(Bus, "recvTiming: src %d dst %d %s 0x%x\n",
 198             src, pkt->getDest(), pkt->cmdString(), pkt->getAddr());
 199
 200     if (!pkt->isExpressSnoop()) {
 201         occupyBus(pkt);
 202     }
 203
 204     short dest = pkt->getDest();
 205     int dest_port_id;
 206     Port *dest_port;
 207
 208     if (dest == Packet::Broadcast) {
 209         dest_port_id = findPort(pkt->getAddr());
 210         dest_port = (dest_port_id == defaultId) ?
 211             defaultPort : interfaces[dest_port_id];
 212         SnoopIter s_end = snoopPorts.end();
 213         for (SnoopIter s_iter = snoopPorts.begin(); s_iter != s_end; s_iter++) {
 214             BusPort *p = *s_iter;
 215             if (p != dest_port && p != src_port) {
 216                 // cache is not allowed to refuse snoop
 217                 bool success M5_VAR_USED = p->sendTiming(pkt);
 218                 assert(success);
 219             }
 220         }
 221     } else {
 222         assert(dest >= 0 && dest < maxId);
 223         assert(dest != src); // catch infinite loops
 224         dest_port_id = dest;
 225         if (dest_port_id == defaultId)
 226             dest_port = defaultPort;
 227         else {
 228             dest_port = checkBusCache(dest);
 229             if (dest_port == NULL) {
 230                 dest_port = interfaces[dest_port_id];
 231             // updateBusCache(dest_port_id, dest_port);
 232             }
 233         }
 234         dest_port = (dest_port_id == defaultId) ?
 235             defaultPort : interfaces[dest_port_id];
 236     }
 237
 238     if (dest_port_id == src) {
 239         // Must be forwarded snoop up from below...
 240         assert(dest == Packet::Broadcast);
 241         assert(src != defaultId); // catch infinite loops
 242     } else {
 243         // send to actual target
 244         if (!dest_port->sendTiming(pkt))  {
 245             // Packet not successfully sent. Leave or put it on the retry list.
 246             // illegal to block responses... can lead to deadlock
 247             assert(!pkt->isResponse());
 248             DPRINTF(Bus, "recvTiming: src %d dst %d %s 0x%x TGT RETRY\n",
 249                     src, pkt->getDest(), pkt->cmdString(), pkt->getAddr());
 250             addToRetryList(src_port);
 251             return false;
 252         }
 253         // send OK, fall through
 254     }
 255
 256     // Packet was successfully sent.
 257     // Also take care of retries
 258     if (inRetry) {
 259         DPRINTF(Bus, "Remove retry from list %d\n", src);
 260         retryList.front()->onRetryList(false);
 261         retryList.pop_front();
 262         inRetry = false;
 263     }
 264     return true;
 265 }
 266
 267 void
 268 Bus::recvRetry(int id)
 269 {
 270     // If there's anything waiting, and the bus isn't busy...
 271     if (retryList.size() && curTick >= tickNextIdle) {
 272         //retryingPort = retryList.front();
 273         inRetry = true;
 274         DPRINTF(Bus, "Sending a retry to %s\n", retryList.front()->getPeer()->name());
 275         retryList.front()->sendRetry();
 276         // If inRetry is still true, sendTiming wasn't called
 277         if (inRetry)
 278         {
 279             retryList.front()->onRetryList(false);
 280             retryList.pop_front();
 281             inRetry = false;
 282
 283             //Bring tickNextIdle up to the present
 284             while (tickNextIdle < curTick)
 285                 tickNextIdle += clock;
 286
 287             //Burn a cycle for the missed grant.
 288             tickNextIdle += clock;
 289
 290             busIdle.reschedule(tickNextIdle, true);
 291         }
 292     }
 293     //If we weren't able to drain before, we might be able to now.
 294     if (drainEvent && retryList.size() == 0 && curTick >= tickNextIdle) {
 295         drainEvent->process();
 296         // Clear the drain event once we're done with it.
 297         drainEvent = NULL;
 298     }
 299 }
 300
 301 int
 302 Bus::findPort(Addr addr)
 303 {
 304     /* An interval tree would be a better way to do this. --ali. */
 305     int dest_id = -1;
 306
 307     dest_id = checkPortCache(addr);
 308     if (dest_id == -1) {
 309         PortIter i = portMap.find(RangeSize(addr,1));
 310         if (i != portMap.end())
 311           dest_id = i->second;
 312         updatePortCache(dest_id, i->first.start, i->first.end);
 313     }
 314
 315     // Check if this matches the default range
 316     if (dest_id == -1) {
 317         AddrRangeIter a_end = defaultRange.end();
 318         for (AddrRangeIter i = defaultRange.begin(); i != a_end; i++) {
 319             if (*i == addr) {
 320                 DPRINTF(Bus, "  found addr %#llx on default\n", addr);
 321                 return defaultId;
 322             }
 323         }
 324
 325         if (responderSet) {
 326             panic("Unable to find destination for addr (user set default "
 327                   "responder): %#llx", addr);
 328         } else {
 329             DPRINTF(Bus, "Unable to find destination for addr: %#llx, will use "
 330                     "default port", addr);
 331
 332             return defaultId;
 333         }
 334     }
 335
 336     return dest_id;
 337 }
 338
 339
 340 /** Function called by the port when the bus is receiving a Atomic
 341  * transaction.*/
 342 Tick
 343 Bus::recvAtomic(PacketPtr pkt)
 344 {
 345     DPRINTF(Bus, "recvAtomic: packet src %d dest %d addr 0x%x cmd %s\n",
 346             pkt->getSrc(), pkt->getDest(), pkt->getAddr(), pkt->cmdString());
 347     assert(pkt->getDest() == Packet::Broadcast);
 348     assert(pkt->isRequest());
 349
 350     // Variables for recording original command and snoop response (if
 351     // any)... if a snooper respondes, we will need to restore
 352     // original command so that additional snoops can take place
 353     // properly
 354     MemCmd orig_cmd = pkt->cmd;
 355     MemCmd snoop_response_cmd = MemCmd::InvalidCmd;
 356     Tick snoop_response_latency = 0;
 357     int orig_src = pkt->getSrc();
 358
 359     int target_port_id = findPort(pkt->getAddr());
 360     BusPort *target_port;
 361     if (target_port_id == defaultId)
 362         target_port = defaultPort;
 363     else {
 364       target_port = checkBusCache(target_port_id);
 365       if (target_port == NULL) {
 366           target_port = interfaces[target_port_id];
 367           updateBusCache(target_port_id, target_port);
 368       }
 369     }
 370
 371     SnoopIter s_end = snoopPorts.end();
 372     for (SnoopIter s_iter = snoopPorts.begin(); s_iter != s_end; s_iter++) {
 373         BusPort *p = *s_iter;
 374         // same port should not have both target addresses and snooping
 375         assert(p != target_port);
 376         if (p->getId() != pkt->getSrc()) {
 377             Tick latency = p->sendAtomic(pkt);
 378             if (pkt->isResponse()) {
 379                 // response from snoop agent
 380                 assert(pkt->cmd != orig_cmd);
 381                 assert(pkt->memInhibitAsserted());
 382                 // should only happen once
 383                 assert(snoop_response_cmd == MemCmd::InvalidCmd);
 384                 // save response state
 385                 snoop_response_cmd = pkt->cmd;
 386                 snoop_response_latency = latency;
 387                 // restore original packet state for remaining snoopers
 388                 pkt->cmd = orig_cmd;
 389                 pkt->setSrc(orig_src);
 390                 pkt->setDest(Packet::Broadcast);
 391             }
 392         }
 393     }
 394
 395     Tick response_latency = 0;
 396
 397     // we can get requests sent up from the memory side of the bus for
 398     // snooping... don't send them back down!
 399     if (target_port_id != pkt->getSrc()) {
 400         response_latency = target_port->sendAtomic(pkt);
 401     }
 402
 403     // if we got a response from a snooper, restore it here
 404     if (snoop_response_cmd != MemCmd::InvalidCmd) {
 405         // no one else should have responded
 406         assert(!pkt->isResponse());
 407         assert(pkt->cmd == orig_cmd);
 408         pkt->cmd = snoop_response_cmd;
 409         response_latency = snoop_response_latency;
 410     }
 411
 412     // why do we have this packet field and the return value both???
 413     pkt->finishTime = curTick + response_latency;
 414     return response_latency;
 415 }
 416
 417 /** Function called by the port when the bus is receiving a Functional
 418  * transaction.*/
 419 void
 420 Bus::recvFunctional(PacketPtr pkt)
 421 {
 422     if (!pkt->isPrint()) {
 423         // don't do DPRINTFs on PrintReq as it clutters up the output
 424         DPRINTF(Bus,
 425                 "recvFunctional: packet src %d dest %d addr 0x%x cmd %s\n",
 426                 pkt->getSrc(), pkt->getDest(), pkt->getAddr(),
 427                 pkt->cmdString());
 428     }
 429     assert(pkt->getDest() == Packet::Broadcast);
 430
 431     int port_id = findPort(pkt->getAddr());
 432     Port *port = (port_id == defaultId) ? defaultPort : interfaces[port_id];
 433     // The packet may be changed by another bus on snoops, restore the
 434     // id after each
 435     int src_id = pkt->getSrc();
 436
 437     assert(pkt->isRequest()); // hasn't already been satisfied
 438
 439     SnoopIter s_end = snoopPorts.end();
 440     for (SnoopIter s_iter = snoopPorts.begin(); s_iter != s_end; s_iter++) {
 441         BusPort *p = *s_iter;
 442         if (p != port && p->getId() != src_id) {
 443             p->sendFunctional(pkt);
 444         }
 445         if (pkt->isResponse()) {
 446             break;
 447         }
 448         pkt->setSrc(src_id);
 449     }
 450
 451     // If the snooping hasn't found what we were looking for, keep going.
 452     if (!pkt->isResponse() && port_id != pkt->getSrc()) {
 453         port->sendFunctional(pkt);
 454     }
 455 }
 456
 457 /** Function called by the port when the bus is receiving a status change.*/
 458 void
 459 Bus::recvStatusChange(Port::Status status, int id)
 460 {
 461     AddrRangeList ranges;
 462     bool snoops;
 463     AddrRangeIter iter;
 464
 465     if (inRecvStatusChange.count(id))
 466         return;
 467     inRecvStatusChange.insert(id);
 468
 469     assert(status == Port::RangeChange &&
 470            "The other statuses need to be implemented.");
 471
 472     DPRINTF(BusAddrRanges, "received RangeChange from device id %d\n", id);
 473
 474     clearPortCache();
 475     if (id == defaultId) {
 476         defaultRange.clear();
 477         // Only try to update these ranges if the user set a default responder.
 478         if (responderSet) {
 479             defaultPort->getPeerAddressRanges(ranges, snoops);
 480             assert(snoops == false);
 481             for(iter = ranges.begin(); iter != ranges.end(); iter++) {
 482                 defaultRange.push_back(*iter);
 483                 DPRINTF(BusAddrRanges, "Adding range %#llx - %#llx for default range\n",
 484                         iter->start, iter->end);
 485             }
 486         }
 487     } else {
 488
 489         assert((id < maxId && id >= 0) || id == defaultId);
 490         BusPort *port = interfaces[id];
 491
 492         // Clean out any previously existent ids
 493         for (PortIter portIter = portMap.begin();
 494              portIter != portMap.end(); ) {
 495             if (portIter->second == id)
 496                 portMap.erase(portIter++);
 497             else
 498                 portIter++;
 499         }
 500
 501         for (SnoopIter s_iter = snoopPorts.begin();
 502              s_iter != snoopPorts.end(); ) {
 503             if ((*s_iter)->getId() == id)
 504                 s_iter = snoopPorts.erase(s_iter);
 505             else
 506                 s_iter++;
 507         }
 508
 509         port->getPeerAddressRanges(ranges, snoops);
 510
 511         if (snoops) {
 512             DPRINTF(BusAddrRanges, "Adding id %d to snoop list\n", id);
 513             snoopPorts.push_back(port);
 514         }
 515
 516         for (iter = ranges.begin(); iter != ranges.end(); iter++) {
 517             DPRINTF(BusAddrRanges, "Adding range %#llx - %#llx for id %d\n",
 518                     iter->start, iter->end, id);
 519             if (portMap.insert(*iter, id) == portMap.end())
 520                 panic("Two devices with same range\n");
 521
 522         }
 523     }
 524     DPRINTF(MMU, "port list has %d entries\n", portMap.size());
 525
 526     // tell all our peers that our address range has changed.
 527     // Don't tell the device that caused this change, it already knows
 528     m5::hash_map<short,BusPort*>::iterator intIter;
 529
 530     for (intIter = interfaces.begin(); intIter != interfaces.end(); intIter++)
 531         if (intIter->first != id && intIter->first != funcPortId)
 532             intIter->second->sendStatusChange(Port::RangeChange);
 533
 534     if (id != defaultId && defaultPort)
 535         defaultPort->sendStatusChange(Port::RangeChange);
 536     inRecvStatusChange.erase(id);
 537 }
 538
 539 void
 540 Bus::addressRanges(AddrRangeList &resp, bool &snoop, int id)
 541 {
 542     resp.clear();
 543     snoop = false;
 544
 545     DPRINTF(BusAddrRanges, "received address range request, returning:\n");
 546
 547     for (AddrRangeIter dflt_iter = defaultRange.begin();
 548          dflt_iter != defaultRange.end(); dflt_iter++) {
 549         resp.push_back(*dflt_iter);
 550         DPRINTF(BusAddrRanges, "  -- Dflt: %#llx : %#llx\n",dflt_iter->start,
 551                 dflt_iter->end);
 552     }
 553     for (PortIter portIter = portMap.begin();
 554          portIter != portMap.end(); portIter++) {
 555         bool subset = false;
 556         for (AddrRangeIter dflt_iter = defaultRange.begin();
 557              dflt_iter != defaultRange.end(); dflt_iter++) {
 558             if ((portIter->first.start < dflt_iter->start &&
 559                 portIter->first.end >= dflt_iter->start) ||
 560                (portIter->first.start < dflt_iter->end &&
 561                 portIter->first.end >= dflt_iter->end))
 562                 fatal("Devices can not set ranges that itersect the default set\
 563                         but are not a subset of the default set.\n");
 564             if (portIter->first.start >= dflt_iter->start &&
 565                 portIter->first.end <= dflt_iter->end) {
 566                 subset = true;
 567                 DPRINTF(BusAddrRanges, "  -- %#llx : %#llx is a SUBSET\n",
 568                     portIter->first.start, portIter->first.end);
 569             }
 570         }
 571         if (portIter->second != id && !subset) {
 572             resp.push_back(portIter->first);
 573             DPRINTF(BusAddrRanges, "  -- %#llx : %#llx\n",
 574                     portIter->first.start, portIter->first.end);
 575         }
 576     }
 577
 578     for (SnoopIter s_iter = snoopPorts.begin(); s_iter != snoopPorts.end();
 579          s_iter++) {
 580         if ((*s_iter)->getId() != id) {
 581             snoop = true;
 582             break;
 583         }
 584     }
 585 }
 586
 587 int
 588 Bus::findBlockSize(int id)
 589 {
 590     if (cachedBlockSizeValid)
 591         return cachedBlockSize;
 592
 593     int max_bs = -1;
 594
 595     PortIter p_end = portMap.end();
 596     for (PortIter p_iter = portMap.begin(); p_iter != p_end; p_iter++) {
 597         int tmp_bs = interfaces[p_iter->second]->peerBlockSize();
 598         if (tmp_bs > max_bs)
 599             max_bs = tmp_bs;
 600     }
 601     SnoopIter s_end = snoopPorts.end();
 602     for (SnoopIter s_iter = snoopPorts.begin(); s_iter != s_end; s_iter++) {
 603         int tmp_bs = (*s_iter)->peerBlockSize();
 604         if (tmp_bs > max_bs)
 605             max_bs = tmp_bs;
 606     }
 607     if (max_bs <= 0)
 608         max_bs = defaultBlockSize;
 609
 610     if (max_bs != 64)
 611         warn_once("Blocksize found to not be 64... hmm... probably not.\n");
 612     cachedBlockSize = max_bs;
 613     cachedBlockSizeValid = true;
 614     return max_bs;
 615 }
 616
 617
 618 unsigned int
 619 Bus::drain(Event * de)
 620 {
 621     //We should check that we're not "doing" anything, and that noone is
 622     //waiting. We might be idle but have someone waiting if the device we
 623     //contacted for a retry didn't actually retry.
 624     if (retryList.size() || (curTick < tickNextIdle && busIdle.scheduled())) {
 625         drainEvent = de;
 626         return 1;
 627     }
 628     return 0;
 629 }
 630
 631 void
 632 Bus::startup()
 633 {
 634     if (tickNextIdle < curTick)
 635         tickNextIdle = (curTick / clock) * clock + clock;
 636 }
 637
 638 Bus *
 639 BusParams::create()
 640 {
 641     return new Bus(this);
 642 }