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/*
* Copyright (c) 2004-2006 The Regents of The University of Michigan
* 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: Kevin Lim
*/
#ifndef __CPU_O3_DECODE_HH__
#define __CPU_O3_DECODE_HH__
#include <queue>
#include "base/statistics.hh"
#include "cpu/timebuf.hh"
struct DerivO3CPUParams;
/**
* DefaultDecode class handles both single threaded and SMT
* decode. Its width is specified by the parameters; each cycles it
* tries to decode that many instructions. Because instructions are
* actually decoded when the StaticInst is created, this stage does
* not do much other than check any PC-relative branches.
*/
template<class Impl>
class DefaultDecode
{
private:
// Typedefs from the Impl.
typedef typename Impl::O3CPU O3CPU;
typedef typename Impl::DynInstPtr DynInstPtr;
typedef typename Impl::CPUPol CPUPol;
// Typedefs from the CPU policy.
typedef typename CPUPol::FetchStruct FetchStruct;
typedef typename CPUPol::DecodeStruct DecodeStruct;
typedef typename CPUPol::TimeStruct TimeStruct;
public:
/** Overall decode stage status. Used to determine if the CPU can
* deschedule itself due to a lack of activity.
*/
enum DecodeStatus {
Active,
Inactive
};
/** Individual thread status. */
enum ThreadStatus {
Running,
Idle,
StartSquash,
Squashing,
Blocked,
Unblocking
};
private:
/** Decode status. */
DecodeStatus _status;
/** Per-thread status. */
ThreadStatus decodeStatus[Impl::MaxThreads];
public:
/** DefaultDecode constructor. */
DefaultDecode(O3CPU *_cpu, DerivO3CPUParams *params);
/** Returns the name of decode. */
std::string name() const;
/** Registers statistics. */
void regStats();
/** Sets the main backwards communication time buffer pointer. */
void setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr);
/** Sets pointer to time buffer used to communicate to the next stage. */
void setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr);
/** Sets pointer to time buffer coming from fetch. */
void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);
/** Sets pointer to list of active threads. */
void setActiveThreads(std::list<ThreadID> *at_ptr);
/** Drains the decode stage. */
bool drain();
/** Resumes execution after a drain. */
void resume() { }
/** Switches out the decode stage. */
void switchOut() { }
/** Takes over from another CPU's thread. */
void takeOverFrom();
/** Ticks decode, processing all input signals and decoding as many
* instructions as possible.
*/
void tick();
/** Determines what to do based on decode's current status.
* @param status_change decode() sets this variable if there was a status
* change (ie switching from from blocking to unblocking).
* @param tid Thread id to decode instructions from.
*/
void decode(bool &status_change, ThreadID tid);
/** Processes instructions from fetch and passes them on to rename.
* Decoding of instructions actually happens when they are created in
* fetch, so this function mostly checks if PC-relative branches are
* correct.
*/
void decodeInsts(ThreadID tid);
private:
/** Inserts a thread's instructions into the skid buffer, to be decoded
* once decode unblocks.
*/
void skidInsert(ThreadID tid);
/** Returns if all of the skid buffers are empty. */
bool skidsEmpty();
/** Updates overall decode status based on all of the threads' statuses. */
void updateStatus();
/** Separates instructions from fetch into individual lists of instructions
* sorted by thread.
*/
void sortInsts();
/** Reads all stall signals from the backwards communication timebuffer. */
void readStallSignals(ThreadID tid);
/** Checks all input signals and updates decode's status appropriately. */
bool checkSignalsAndUpdate(ThreadID tid);
/** Checks all stall signals, and returns if any are true. */
bool checkStall(ThreadID tid) const;
/** Returns if there any instructions from fetch on this cycle. */
inline bool fetchInstsValid();
/** Switches decode to blocking, and signals back that decode has
* become blocked.
* @return Returns true if there is a status change.
*/
bool block(ThreadID tid);
/** Switches decode to unblocking if the skid buffer is empty, and
* signals back that decode has unblocked.
* @return Returns true if there is a status change.
*/
bool unblock(ThreadID tid);
/** Squashes if there is a PC-relative branch that was predicted
* incorrectly. Sends squash information back to fetch.
*/
void squash(DynInstPtr &inst, ThreadID tid);
public:
/** Squashes due to commit signalling a squash. Changes status to
* squashing and clears block/unblock signals as needed.
*/
unsigned squash(ThreadID tid);
private:
// Interfaces to objects outside of decode.
/** CPU interface. */
O3CPU *cpu;
/** Time buffer interface. */
TimeBuffer<TimeStruct> *timeBuffer;
/** Wire to get rename's output 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;
/** Wire to write information heading to previous stages. */
// Might not be the best name as not only fetch will read it.
typename TimeBuffer<TimeStruct>::wire toFetch;
/** Decode instruction queue. */
TimeBuffer<DecodeStruct> *decodeQueue;
/** Wire used to write any information heading to rename. */
typename TimeBuffer<DecodeStruct>::wire toRename;
/** Fetch instruction queue interface. */
TimeBuffer<FetchStruct> *fetchQueue;
/** Wire to get fetch's output from fetch queue. */
typename TimeBuffer<FetchStruct>::wire fromFetch;
/** Queue of all instructions coming from fetch this cycle. */
std::queue<DynInstPtr> insts[Impl::MaxThreads];
/** Skid buffer between fetch and decode. */
std::queue<DynInstPtr> skidBuffer[Impl::MaxThreads];
/** Variable that tracks if decode has written to the time buffer this
* cycle. Used to tell CPU if there is activity this cycle.
*/
bool wroteToTimeBuffer;
/** Source of possible stalls. */
struct Stalls {
bool rename;
bool iew;
bool commit;
};
/** Tracks which stages are telling decode to stall. */
Stalls stalls[Impl::MaxThreads];
/** Rename to decode delay. */
Cycles renameToDecodeDelay;
/** IEW to decode delay. */
Cycles iewToDecodeDelay;
/** Commit to decode delay. */
Cycles commitToDecodeDelay;
/** Fetch to decode delay. */
Cycles fetchToDecodeDelay;
/** The width of decode, in instructions. */
unsigned decodeWidth;
/** Index of instructions being sent to rename. */
unsigned toRenameIndex;
/** number of Active Threads*/
ThreadID numThreads;
/** List of active thread ids */
std::list<ThreadID> *activeThreads;
/** Number of branches in flight. */
unsigned branchCount[Impl::MaxThreads];
/** Maximum size of the skid buffer. */
unsigned skidBufferMax;
/** SeqNum of Squashing Branch Delay Instruction (used for MIPS)*/
Addr bdelayDoneSeqNum[Impl::MaxThreads];
/** Instruction used for squashing branch (used for MIPS)*/
DynInstPtr squashInst[Impl::MaxThreads];
/** Tells when their is a pending delay slot inst. to send
* to rename. If there is, then wait squash after the next
* instruction (used for MIPS).
*/
bool squashAfterDelaySlot[Impl::MaxThreads];
/** Stat for total number of idle cycles. */
Stats::Scalar decodeIdleCycles;
/** Stat for total number of blocked cycles. */
Stats::Scalar decodeBlockedCycles;
/** Stat for total number of normal running cycles. */
Stats::Scalar decodeRunCycles;
/** Stat for total number of unblocking cycles. */
Stats::Scalar decodeUnblockCycles;
/** Stat for total number of squashing cycles. */
Stats::Scalar decodeSquashCycles;
/** Stat for number of times a branch is resolved at decode. */
Stats::Scalar decodeBranchResolved;
/** Stat for number of times a branch mispredict is detected. */
Stats::Scalar decodeBranchMispred;
/** Stat for number of times decode detected a non-control instruction
* incorrectly predicted as a branch.
*/
Stats::Scalar decodeControlMispred;
/** Stat for total number of decoded instructions. */
Stats::Scalar decodeDecodedInsts;
/** Stat for total number of squashed instructions. */
Stats::Scalar decodeSquashedInsts;
};
#endif // __CPU_O3_DECODE_HH__
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