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40 * Authors: Ron Dreslinski
48 * Declaration of an abstract crossbar base class.
51 #ifndef __MEM_XBAR_HH__
52 #define __MEM_XBAR_HH__
55 #include <unordered_map>
57 #include "base/addr_range_map.hh"
58 #include "base/types.hh"
59 #include "mem/mem_object.hh"
60 #include "mem/qport.hh"
61 #include "params/BaseXBar.hh"
62 #include "sim/stats.hh"
65 * The base crossbar contains the common elements of the non-coherent
66 * and coherent crossbar. It is an abstract class that does not have
67 * any of the functionality relating to the actual reception and
68 * transmission of packets, as this is left for the subclasses.
70 * The BaseXBar is responsible for the basic flow control (busy or
71 * not), the administration of retries, and the address decoding.
73 class BaseXBar : public MemObject
79 * A layer is an internal crossbar arbitration point with its own
80 * flow control. Each layer is a converging multiplexer tree. By
81 * instantiating one layer per destination port (and per packet
82 * type, i.e. request, response, snoop request and snoop
83 * response), we model full crossbar structures like AXI, ACE,
86 * The template parameter, PortClass, indicates the destination
87 * port type for the layer. The retry list holds either master
88 * ports or slave ports, depending on the direction of the
89 * layer. Thus, a request layer has a retry list containing slave
90 * ports, whereas a response layer holds master ports.
92 template <typename SrcType, typename DstType>
93 class Layer : public Drainable
99 * Create a layer and give it a name. The layer uses
100 * the crossbar an event manager.
102 * @param _port destination port the layer converges at
103 * @param _xbar the crossbar this layer belongs to
104 * @param _name the layer's name
106 Layer(DstType& _port, BaseXBar& _xbar, const std::string& _name);
109 * Drain according to the normal semantics, so that the crossbar
110 * can tell the layer to drain, and pass an event to signal
113 * @param de drain event to call once drained
115 * @return 1 if busy or waiting to retry, or 0 if idle
117 DrainState drain() override;
119 const std::string name() const { return xbar.name() + _name; }
123 * Determine if the layer accepts a packet from a specific
124 * port. If not, the port in question is also added to the
125 * retry list. In either case the state of the layer is
126 * updated accordingly.
128 * @param port Source port presenting the packet
130 * @return True if the layer accepts the packet
132 bool tryTiming(SrcType* src_port);
135 * Deal with a destination port accepting a packet by potentially
136 * removing the source port from the retry list (if retrying) and
137 * occupying the layer accordingly.
139 * @param busy_time Time to spend as a result of a successful send
141 void succeededTiming(Tick busy_time);
144 * Deal with a destination port not accepting a packet by
145 * potentially adding the source port to the retry list (if
146 * not already at the front) and occupying the layer
149 * @param src_port Source port
150 * @param busy_time Time to spend as a result of a failed send
152 void failedTiming(SrcType* src_port, Tick busy_time);
154 void occupyLayer(Tick until);
157 * Send a retry to the port at the head of waitingForLayer. The
158 * caller must ensure that the list is not empty.
163 * Handle a retry from a neighbouring module. This wraps
164 * retryWaiting by verifying that there are ports waiting
165 * before calling retryWaiting.
174 * Sending the actual retry, in a manner specific to the
175 * individual layers. Note that for a MasterPort, there is
176 * both a RequestLayer and a SnoopResponseLayer using the same
177 * port, but using different functions for the flow control.
179 virtual void sendRetry(SrcType* retry_port) = 0;
183 /** The destination port this layer converges at. */
186 /** The crossbar this layer is a part of. */
192 * We declare an enum to track the state of the layer. The
193 * starting point is an idle state where the layer is waiting
194 * for a packet to arrive. Upon arrival, the layer
195 * transitions to the busy state, where it remains either
196 * until the packet transfer is done, or the header time is
197 * spent. Once the layer leaves the busy state, it can
198 * either go back to idle, if no packets have arrived while it
199 * was busy, or the layer goes on to retry the first port
200 * in waitingForLayer. A similar transition takes place from
201 * idle to retry if the layer receives a retry from one of
202 * its connected ports. The retry state lasts until the port
203 * in questions calls sendTiming and returns control to the
204 * layer, or goes to a busy state if the port does not
205 * immediately react to the retry by calling sendTiming.
207 enum State { IDLE, BUSY, RETRY };
212 * A deque of ports that retry should be called on because
213 * the original send was delayed due to a busy layer.
215 std::deque<SrcType*> waitingForLayer;
218 * Track who is waiting for the retry when receiving it from a
219 * peer. If no port is waiting NULL is stored.
221 SrcType* waitingForPeer;
224 * Release the layer after being occupied and return to an
225 * idle state where we proceed to send a retry to any
226 * potential waiting port, or drain if asked to do so.
229 EventFunctionWrapper releaseEvent;
232 * Stats for occupancy and utilization. These stats capture
233 * the time the layer spends in the busy state and are thus only
234 * relevant when the memory system is in timing mode.
236 Stats::Scalar occupancy;
237 Stats::Formula utilization;
241 class ReqLayer : public Layer<SlavePort, MasterPort>
245 * Create a request layer and give it a name.
247 * @param _port destination port the layer converges at
248 * @param _xbar the crossbar this layer belongs to
249 * @param _name the layer's name
251 ReqLayer(MasterPort& _port, BaseXBar& _xbar, const std::string& _name) :
252 Layer(_port, _xbar, _name)
257 sendRetry(SlavePort* retry_port) override
259 retry_port->sendRetryReq();
263 class RespLayer : public Layer<MasterPort, SlavePort>
267 * Create a response layer and give it a name.
269 * @param _port destination port the layer converges at
270 * @param _xbar the crossbar this layer belongs to
271 * @param _name the layer's name
273 RespLayer(SlavePort& _port, BaseXBar& _xbar,
274 const std::string& _name) :
275 Layer(_port, _xbar, _name)
280 sendRetry(MasterPort* retry_port) override
282 retry_port->sendRetryResp();
286 class SnoopRespLayer : public Layer<SlavePort, MasterPort>
290 * Create a snoop response layer and give it a name.
292 * @param _port destination port the layer converges at
293 * @param _xbar the crossbar this layer belongs to
294 * @param _name the layer's name
296 SnoopRespLayer(MasterPort& _port, BaseXBar& _xbar,
297 const std::string& _name) :
298 Layer(_port, _xbar, _name)
304 sendRetry(SlavePort* retry_port) override
306 retry_port->sendRetrySnoopResp();
311 * Cycles of front-end pipeline including the delay to accept the request
312 * and to decode the address.
314 const Cycles frontendLatency;
315 const Cycles forwardLatency;
316 const Cycles responseLatency;
317 /** the width of the xbar in bytes */
318 const uint32_t width;
320 AddrRangeMap<PortID, 3> portMap;
323 * Remember where request packets came from so that we can route
324 * responses to the appropriate port. This relies on the fact that
325 * the underlying Request pointer inside the Packet stays
328 std::unordered_map<RequestPtr, PortID> routeTo;
330 /** all contigous ranges seen by this crossbar */
331 AddrRangeList xbarRanges;
333 AddrRange defaultRange;
336 * Function called by the port when the crossbar is recieving a
339 * @param master_port_id id of the port that received the change
341 virtual void recvRangeChange(PortID master_port_id);
344 * Find which port connected to this crossbar (if any) should be
345 * given a packet with this address range.
347 * @param addr_range Address range to find port for.
348 * @return id of port that the packet should be sent out of.
350 PortID findPort(AddrRange addr_range);
353 * Return the address ranges the crossbar is responsible for.
355 * @return a list of non-overlapping address ranges
357 AddrRangeList getAddrRanges() const;
360 * Calculate the timing parameters for the packet. Updates the
361 * headerDelay and payloadDelay fields of the packet
362 * object with the relative number of ticks required to transmit
363 * the header and the payload, respectively.
365 * @param pkt Packet to populate with timings
366 * @param header_delay Header delay to be added
368 void calcPacketTiming(PacketPtr pkt, Tick header_delay);
371 * Remember for each of the master ports of the crossbar if we got
372 * an address range from the connected slave. For convenience,
373 * also keep track of if we got ranges from all the slave modules
376 std::vector<bool> gotAddrRanges;
377 bool gotAllAddrRanges;
379 /** The master and slave ports of the crossbar */
380 std::vector<QueuedSlavePort*> slavePorts;
381 std::vector<MasterPort*> masterPorts;
383 /** Port that handles requests that don't match any of the interfaces.*/
384 PortID defaultPortID;
386 /** If true, use address range provided by default device. Any
387 address not handled by another port and not in default device's
388 range will cause a fatal error. If false, just send all
389 addresses not handled by another port to default device. */
390 const bool useDefaultRange;
392 BaseXBar(const BaseXBarParams *p);
395 * Stats for transaction distribution and data passing through the
396 * crossbar. The transaction distribution is globally counting
397 * different types of commands. The packet count and total packet
398 * size are two-dimensional vectors that are indexed by the
399 * slave port and master port id (thus the neighbouring master and
400 * neighbouring slave), summing up both directions (request and
403 Stats::Vector transDist;
404 Stats::Vector2d pktCount;
405 Stats::Vector2d pktSize;
411 void init() override;
413 /** A function used to return the port associated with this object. */
414 Port &getPort(const std::string &if_name,
415 PortID idx=InvalidPortID) override;
417 void regStats() override;
420 #endif //__MEM_XBAR_HH__