(*intIter)->sendStatusChange(Port::RangeChange);
}
+Bus::BusFreeEvent::BusFreeEvent(Bus *_bus) : Event(&mainEventQueue), bus(_bus)
+{}
+
+void Bus::BusFreeEvent::process()
+{
+ bus->recvRetry(0);
+}
+
+const char * Bus::BusFreeEvent::description()
+{
+ return "bus became available";
+}
+
+void
+Bus::occupyBus(int numCycles)
+{
+ //Move up when the bus will next be free
+ //We avoid the use of divide by adding repeatedly
+ //This should be faster if the value is updated frequently, but should
+ //be may be slower otherwise.
+
+ //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. Anthing that happens later will have to "wait" for the
+ //end of that cycle, and then start using the bus after that.
+ while (tickNextIdle < curTick)
+ tickNextIdle += clock;
+ //Advance it numCycles bus cycles.
+ //XXX Should this use the repeating add trick as well?
+ tickNextIdle += (numCycles * clock);
+ if (!busIdle.scheduled()) {
+ busIdle.schedule(tickNextIdle);
+ } else {
+ busIdle.reschedule(tickNextIdle);
+ }
+}
/** Function called by the port when the bus is receiving a Timing
* transaction.*/
DPRINTF(Bus, "recvTiming: packet src %d dest %d addr 0x%x cmd %s\n",
pkt->getSrc(), pkt->getDest(), pkt->getAddr(), pkt->cmdString());
- short dest = pkt->getDest();
- //if (pkt->isRequest() && curTick < tickAddrLastUsed ||
- // (pkt->isResponse() || pkt->hasData()) && curTick < tickDataLastUsed) {
- //We're going to need resources that have already been committed
- //Send this guy to the back of the line
- //We don't need to worry about scheduling an event to deal with when the
- //bus is freed because that's handled when tick*LastUsed is incremented.
- // retryList.push_back(interfaces[pkt->getSrc()]);
- // return false;
- //}
+ Port *pktPort = interfaces[pkt->getSrc()];
- if (dest == Packet::Broadcast) {
- if ( timingSnoopPhase1(pkt) )
- {
- timingSnoopPhase2(pkt);
- port = findPort(pkt->getAddr(), pkt->getSrc());
- }
- else
- {
- //Snoop didn't succeed
- retryList.push_back(interfaces[pkt->getSrc()]);
- return false;
+ // If the bus is busy, or other devices are in line ahead of the current one,
+ // put this device on the retry list.
+ if (tickNextIdle > curTick || (retryList.size() && pktPort != retryingPort)) {
+ addToRetryList(pktPort);
+ return false;
+ }
+
+ // If the bus is blocked, make the device wait.
+ if (!(port = findDestPort(pkt, pkt->getSrc()))) {
+ addToRetryList(pktPort);
+ return false;
+ }
+
+ // The packet will be sent. Figure out how long it occupies the bus.
+ int numCycles = 0;
+ // Requests need one cycle to send an address
+ if (pkt->isRequest())
+ numCycles++;
+ else if (pkt->isResponse() || pkt->hasData()) {
+ // If a packet has data, it needs ceil(size/width) cycles to send it
+ // We're using the "adding instead of dividing" trick again here
+ if (pkt->hasData()) {
+ int dataSize = pkt->getSize();
+ for (int transmitted = 0; transmitted < dataSize;
+ transmitted += width) {
+ numCycles++;
+ }
+ } else {
+ // If the packet didn't have data, it must have been a response.
+ // Those use the bus for one cycle to send their data.
+ numCycles++;
}
- } else {
- assert(dest >= 0 && dest < interfaces.size());
- assert(dest != pkt->getSrc()); // catch infinite loops
- port = interfaces[dest];
}
+ occupyBus(numCycles);
if (port->sendTiming(pkt)) {
- // Packet was successfully sent.
- // Figure out what resources were used, and then return true.
- //if (pkt->isRequest()) {
- // The address bus will be used for one cycle
- // while (tickAddrLastUsed <= curTick)
- // tickAddrLastUsed += clock;
- //}
- //if (pkt->isResponse() || pkt->hasData()) {
- // Use up the data bus for at least one bus cycle
- // while (tickDataLastUsed <= curTick)
- // tickDataLastUsed += clock;
- // Use up the data bus for however many cycles remain
- // if (pkt->hasData()) {
- // int dataSize = pkt->getSize();
- // for (int transmitted = width; transmitted < dataSize;
- // transmitted += width) {
- // tickDataLastUsed += clock;
- // }
- // }
- //}
+ // Packet was successfully sent. Return true.
return true;
}
- // packet not successfully sent
- retryList.push_back(interfaces[pkt->getSrc()]);
+ // Packet not successfully sent. Leave or put it on the retry list.
+ addToRetryList(pktPort);
return false;
}
void
Bus::recvRetry(int id)
{
- // Go through all the elements on the list calling sendRetry on each
- // This is not very efficient at all but it works. Ultimately we should end
- // up with something that is more intelligent.
- int initialSize = retryList.size();
- int i;
- Port *p;
-
- for (i = 0; i < initialSize; i++) {
- assert(retryList.size() > 0);
- p = retryList.front();
- retryList.pop_front();
- p->sendRetry();
+ //If there's anything waiting...
+ if (retryList.size()) {
+ retryingPort = retryList.front();
+ retryingPort->sendRetry();
+ //If the retryingPort pointer isn't null, either sendTiming wasn't
+ //called, or it was and the packet was successfully sent.
+ if (retryingPort) {
+ retryList.pop_front();
+ retryingPort = 0;
+ }
}
}
+Port *
+Bus::findDestPort(PacketPtr pkt, int id)
+{
+ Port * port = NULL;
+ short dest = pkt->getDest();
+
+ if (dest == Packet::Broadcast) {
+ if (timingSnoopPhase1(pkt)) {
+ timingSnoopPhase2(pkt);
+ port = findPort(pkt->getAddr(), pkt->getSrc());
+ }
+ //else, port stays NULL
+ } else {
+ assert(dest >= 0 && dest < interfaces.size());
+ assert(dest != pkt->getSrc()); // catch infinite loops
+ port = interfaces[dest];
+ }
+ return port;
+}
Port *
Bus::findPort(Addr addr, int id)
#include "mem/packet.hh"
#include "mem/port.hh"
#include "mem/request.hh"
+#include "sim/eventq.hh"
class Bus : public MemObject
{
int clock;
/** the width of the bus in bits */
int width;
- /** the last tick the address bus was used */
- Tick tickAddrLastUsed;
- /** the last tick the data bus was used */
- Tick tickDataLastUsed;
+ /** the next tick at which the bus will be idle */
+ Tick tickNextIdle;
static const int defaultId = -1;
*/
Port *findPort(Addr addr, int id);
+ /** Finds the port a packet should be sent to. If the bus is blocked, no port
+ * is returned.
+ * @param pkt Packet to find a destination port for.
+ * @param id Id of the port this packet was received from
+ * (to prevent loops)
+ */
+
+ Port *findDestPort(PacketPtr pkt, int id);
+
/** Find all ports with a matching snoop range, except src port. Keep in mind
* that the ranges shouldn't overlap or you will get a double snoop to the same
* interface.and the cache will assert out.
};
+ class BusFreeEvent : public Event
+ {
+ Bus * bus;
+
+ public:
+ BusFreeEvent(Bus * _bus);
+ void process();
+ const char *description();
+ };
+
+ BusFreeEvent busIdle;
+
+ void occupyBus(int numCycles);
+
+ Port * retryingPort;
+
/** An array of pointers to the peer port interfaces
connected to this bus.*/
std::vector<Port*> interfaces;
* original send failed for whatever reason.*/
std::list<Port*> retryList;
+ void addToRetryList(Port * port)
+ {
+ if (!retryingPort) {
+ // The device wasn't retrying a packet, or wasn't at an appropriate
+ // time.
+ retryList.push_back(port);
+ } else {
+ // The device was retrying a packet. It didn't work, so we'll leave
+ // it at the head of the retry list.
+ retryingPort = 0;
+
+ // We shouldn't be receiving a packet from one port when a different
+ // one is retrying.
+ assert(port == retryingPort);
+ }
+ }
+
/** Port that handles requests that don't match any of the interfaces.*/
Port *defaultPort;
Bus(const std::string &n, int bus_id, int _clock, int _width)
: MemObject(n), busId(bus_id), clock(_clock), width(_width),
- tickAddrLastUsed(0), tickDataLastUsed(0), defaultPort(NULL)
+ tickNextIdle(0), busIdle(this), retryingPort(0), defaultPort(NULL)
{
+ //Both the width and clock period must be positive
assert(width);
+ assert(clock);
}
};
projects / gem5.git / commitdiff