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// Todo: add in statistics, only get the MachInst and let decode actually
// decode, think about SMT fetch,
// fix up branch prediction stuff into one thing,
// Figure out where to advance time buffer. Add a way to get a
// stage's current status.
#ifndef __CPU_BETA_CPU_SIMPLE_FETCH_HH__
#define __CPU_BETA_CPU_SIMPLE_FETCH_HH__
//Will want to include: time buffer, structs, MemInterface, Event,
//whatever class bzero uses, MemReqPtr
#include "base/statistics.hh"
#include "base/timebuf.hh"
#include "cpu/pc_event.hh"
#include "mem/mem_interface.hh"
#include "sim/eventq.hh"
/**
* SimpleFetch class to fetch a single instruction each cycle. SimpleFetch
* will stall if there's an Icache miss, but otherwise assumes a one cycle
* Icache hit.
*/
template <class Impl>
class SimpleFetch
{
public:
/** Typedefs from Impl. */
typedef typename Impl::ISA ISA;
typedef typename Impl::CPUPol CPUPol;
typedef typename Impl::DynInst DynInst;
typedef typename Impl::DynInstPtr DynInstPtr;
typedef typename Impl::FullCPU FullCPU;
typedef typename Impl::Params Params;
typedef typename CPUPol::BPredUnit BPredUnit;
typedef typename CPUPol::FetchStruct FetchStruct;
typedef typename CPUPol::TimeStruct TimeStruct;
/** Typedefs from ISA. */
typedef typename ISA::MachInst MachInst;
public:
enum Status {
Running,
Idle,
Squashing,
Blocked,
IcacheMissStall,
IcacheMissComplete
};
// May eventually need statuses on a per thread basis.
Status _status;
bool stalled;
public:
/** SimpleFetch constructor. */
SimpleFetch(Params ¶ms);
void regStats();
void setCPU(FullCPU *cpu_ptr);
void setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer);
void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);
void tick();
void fetch();
void processCacheCompletion();
// Figure out PC vs next PC and how it should be updated
void squash(const Addr &new_PC);
private:
inline void doSquash(const Addr &new_PC);
void squashFromDecode(const Addr &new_PC, const InstSeqNum &seq_num);
/**
* Looks up in the branch predictor to see if the next PC should be
* either next PC+=MachInst or a branch target.
* @params next_PC Next PC variable passed in by reference. It is
* expected to be set to the current PC; it will be updated with what
* the next PC will be.
* @return Whether or not a branch was predicted as taken.
*/
bool lookupAndUpdateNextPC(DynInstPtr &inst, Addr &next_PC);
/**
* Fetches the cache line that contains fetch_PC. Returns any
* fault that happened. Puts the data into the class variable
* cacheData.
* @params fetch_PC The PC address that is being fetched from.
* @return Any fault that occured.
*/
Fault fetchCacheLine(Addr fetch_PC);
// Align an address (typically a PC) to the start of an I-cache block.
// We fold in the PISA 64- to 32-bit conversion here as well.
Addr icacheBlockAlignPC(Addr addr)
{
addr = ISA::realPCToFetchPC(addr);
return (addr & ~(cacheBlkMask));
}
public:
class CacheCompletionEvent : public Event
{
private:
SimpleFetch *fetch;
public:
CacheCompletionEvent(SimpleFetch *_fetch);
virtual void process();
virtual const char *description();
};
// CacheCompletionEvent cacheCompletionEvent;
private:
/** Pointer to the FullCPU. */
FullCPU *cpu;
/** Time buffer interface. */
TimeBuffer<TimeStruct> *timeBuffer;
/** Wire to get decode's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromDecode;
/** Wire to get rename's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromRename;
/** Wire to get iew's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromIEW;
/** Wire to get commit's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromCommit;
/** Internal fetch instruction queue. */
TimeBuffer<FetchStruct> *fetchQueue;
//Might be annoying how this name is different than the queue.
/** Wire used to write any information heading to decode. */
typename TimeBuffer<FetchStruct>::wire toDecode;
/** Icache interface. */
MemInterface *icacheInterface;
/** BPredUnit. */
BPredUnit branchPred;
/** Memory request used to access cache. */
MemReqPtr memReq;
/** Decode to fetch delay, in ticks. */
unsigned decodeToFetchDelay;
/** Rename to fetch delay, in ticks. */
unsigned renameToFetchDelay;
/** IEW to fetch delay, in ticks. */
unsigned iewToFetchDelay;
/** Commit to fetch delay, in ticks. */
unsigned commitToFetchDelay;
/** The width of fetch in instructions. */
unsigned fetchWidth;
/** Cache block size. */
int cacheBlkSize;
/** Mask to get a cache block's address. */
Addr cacheBlkMask;
/** The cache line being fetched. */
uint8_t *cacheData;
/** Size of instructions. */
int instSize;
/** Icache stall statistics. */
Counter lastIcacheStall;
Stats::Scalar<> icacheStallCycles;
Stats::Scalar<> fetchedInsts;
Stats::Scalar<> predictedBranches;
Stats::Scalar<> fetchCycles;
Stats::Scalar<> fetchSquashCycles;
Stats::Scalar<> fetchBlockedCycles;
Stats::Scalar<> fetchedCacheLines;
Stats::Distribution<> fetch_nisn_dist;
};
#endif //__CPU_BETA_CPU_SIMPLE_FETCH_HH__
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