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https://github.com/openhwgroup/cvw
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Two bit predictor cleanup.
This commit is contained in:
Ross Thompson
parent
87c9682311
commit
bca87d326b
@ -67,7 +67,7 @@ module bpred (
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);
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logic BTBValidF;
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logic [1:0] BPPredF, BPPredD, BPPredE, UpdateBPPredE;
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logic [1:0] DirPredictionF, DirPredictionD, DirPredictionE, UpdateBPPredE;
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logic [4:0] BPInstrClassF, BPInstrClassD, BPInstrClassE;
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logic [`XLEN-1:0] BTBPredPCF, RASPCF;
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@ -87,22 +87,18 @@ module bpred (
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// Part 1 branch direction prediction
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// look into the 2 port Sram model. something is wrong.
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if (`BPTYPE == "BPTWOBIT") begin:Predictor
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twoBitPredictor DirPredictor(.clk, .reset, .StallF,
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.LookUpPC(PCNextF),
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.Prediction(BPPredF),
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// update
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.UpdatePC(PCE),
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.UpdateEN(InstrClassE[0] & ~StallE),
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.UpdatePrediction(UpdateBPPredE));
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twoBitPredictor DirPredictor(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .FlushD, .FlushE, .FlushM,
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.PCNextF, .PCM, .DirPredictionF(DirPredictionF), .DirPredictionWrongE(BPPredDirWrongE),
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.BranchInstrE(InstrClassE[0]), .BranchInstrM(InstrClassM[0]), .PCSrcE);
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end else if (`BPTYPE == "BPGLOBAL") begin:Predictor
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globalhistory DirPredictor(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .FlushD, .FlushE, .FlushM,
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.PCNextF, .PCM, .DirPredictionF(BPPredF), .DirPredictionWrongE(BPPredDirWrongE),
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.PCNextF, .PCM, .DirPredictionF(DirPredictionF), .DirPredictionWrongE(BPPredDirWrongE),
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.BranchInstrE(InstrClassE[0]), .BranchInstrM(InstrClassM[0]), .PCSrcE);
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end else if (`BPTYPE == "BPGSHARE") begin:Predictor
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gshare DirPredictor(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .FlushD, .FlushE, .FlushM,
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.PCNextF, .PCM, .DirPredictionF(BPPredF), .DirPredictionWrongE(BPPredDirWrongE),
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.PCNextF, .PCM, .DirPredictionF(DirPredictionF), .DirPredictionWrongE(BPPredDirWrongE),
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.BranchInstrE(InstrClassE[0]), .BranchInstrM(InstrClassM[0]), .PCSrcE);
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end
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else if (`BPTYPE == "BPLOCALPAg") begin:Predictor
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@ -110,7 +106,7 @@ module bpred (
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localHistoryPredictor DirPredictor(.clk,
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.reset, .StallF, .StallE,
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.LookUpPC(PCNextF),
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.Prediction(BPPredF),
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.Prediction(DirPredictionF),
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// update
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.UpdatePC(PCE),
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.UpdateEN(InstrClassE[0] & ~StallE),
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@ -123,7 +119,7 @@ module bpred (
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// 1) A direction (1 = Taken, 0 = Not Taken)
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// 2) Any information which is necessary for the predictor to build its next state.
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// For a 2 bit table this is the prediction count.
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assign SelBPPredF = ((BPInstrClassF[0] & BPPredF[1] & BTBValidF) |
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assign SelBPPredF = ((BPInstrClassF[0] & DirPredictionF[1] & BTBValidF) |
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BPInstrClassF[3] |
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(BPInstrClassF[2] & BTBValidF) |
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BPInstrClassF[1] & BTBValidF) ;
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@ -164,14 +160,14 @@ module bpred (
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flopenr #(2) BPPredRegD(.clk(clk),
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.reset(reset),
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.en(~StallD),
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.d(BPPredF),
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.q(BPPredD));
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.d(DirPredictionF),
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.q(DirPredictionD));
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flopenr #(2) BPPredRegE(.clk(clk),
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.reset(reset),
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.en(~StallE),
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.d(BPPredD),
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.q(BPPredE));
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.d(DirPredictionD),
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.q(DirPredictionE));
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// the branch predictor needs a compact decoding of the instruction class.
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@ -225,7 +221,7 @@ module bpred (
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assign BPPredClassNonCFIWrongE = PredictionInstrClassWrongE & ~|InstrClassE;
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// 2 bit saturating counter
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satCounter2 BPDirUpdate(.BrDir(PCSrcE), .OldState(BPPredE), .NewState(UpdateBPPredE));
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satCounter2 BPDirUpdate(.BrDir(PCSrcE), .OldState(DirPredictionE), .NewState(UpdateBPPredE));
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// Selects the BP or PC+2/4.
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mux2 #(`XLEN) pcmux0(PCPlus2or4F, BPPredPCF, SelBPPredF, PCNext0F);
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@ -33,58 +33,49 @@
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`include "wally-config.vh"
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module twoBitPredictor
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#(parameter int Depth = 10
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#(parameter int k = 10
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)
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(input logic clk,
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input logic reset,
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input logic StallF,
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input logic [`XLEN-1:0] LookUpPC,
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output logic [1:0] Prediction,
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// update
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input logic [`XLEN-1:0] UpdatePC,
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input logic UpdateEN,
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input logic [1:0] UpdatePrediction
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input logic StallF, StallD, StallE, StallM,
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input logic FlushD, FlushE, FlushM,
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input logic [`XLEN-1:0] PCNextF, PCM,
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output logic [1:0] DirPredictionF,
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output logic DirPredictionWrongE,
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input logic BranchInstrE, BranchInstrM,
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input logic PCSrcE
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);
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logic [Depth-1:0] LookUpPCIndex, UpdatePCIndex;
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logic [k-1:0] IndexNextF, IndexM;
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logic [1:0] PredictionMemory;
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logic DoForwarding, DoForwardingF;
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logic [1:0] UpdatePredictionF;
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logic [1:0] DirPredictionD, DirPredictionE;
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logic [1:0] NewDirPredictionE, NewDirPredictionM;
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// hashing function for indexing the PC
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// We have Depth bits to index, but XLEN bits as the input.
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// We have k bits to index, but XLEN bits as the input.
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// bit 0 is always 0, bit 1 is 0 if using 4 byte instructions, but is not always 0 if
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// using compressed instructions. XOR bit 1 with the MSB of index.
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assign UpdatePCIndex = {UpdatePC[Depth+1] ^ UpdatePC[1], UpdatePC[Depth:2]};
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assign LookUpPCIndex = {LookUpPC[Depth+1] ^ LookUpPC[1], LookUpPC[Depth:2]};
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assign IndexNextF = {PCNextF[k+1] ^ PCNextF[1], PCNextF[k:2]};
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assign IndexM = {PCM[k+1] ^ PCM[1], PCM[k:2]};
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ram2p1r1wb #(Depth, 2) PHT(.clk(clk),
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.reset(reset),
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.ra1(LookUpPCIndex),
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.rd1(PredictionMemory),
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.ren1(~StallF),
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.wa2(UpdatePCIndex),
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.wd2(UpdatePrediction),
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.wen2(UpdateEN),
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.bwe2(2'b11));
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ram2p1r1wbefix #(2**k, 2) PHT(.clk(clk),
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.ce1(~StallF), .ce2(~StallM & ~FlushM),
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.ra1(IndexNextF),
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.rd1(DirPredictionF),
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.wa2(IndexM),
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.wd2(NewDirPredictionM),
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.we2(BranchInstrM & ~StallM & ~FlushM),
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.bwe2(1'b1));
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// need to forward when updating to the same address as reading.
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// first we compare to see if the update and lookup addreses are the same
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assign DoForwarding = UpdatePCIndex == LookUpPCIndex;
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flopenrc #(2) PredictionRegD(clk, reset, FlushD, ~StallD, DirPredictionF, DirPredictionD);
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flopenrc #(2) PredictionRegE(clk, reset, FlushE, ~StallE, DirPredictionD, DirPredictionE);
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// register the update value and the forwarding signal into the Fetch stage
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flopr #(1) DoForwardingReg(.clk(clk),
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.reset(reset),
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.d(DoForwarding),
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.q(DoForwardingF));
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assign DirPredictionWrongE = PCSrcE != DirPredictionE[1] & BranchInstrE;
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flopr #(2) UpdatePredictionReg(.clk(clk),
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.reset(reset),
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.d(UpdatePrediction),
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.q(UpdatePredictionF));
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satCounter2 BPDirUpdateE(.BrDir(PCSrcE), .OldState(DirPredictionE), .NewState(NewDirPredictionE));
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flopenrc #(2) NewPredictionRegM(clk, reset, FlushM, ~StallM, NewDirPredictionE, NewDirPredictionM);
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assign Prediction = DoForwardingF ? UpdatePredictionF : PredictionMemory;
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endmodule
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