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Minor optimization to btb.

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This commit is contained in:
Ross Thompson 2023-01-31 22:03:51 -06:00
parent 81b280576f
commit 8a6eaa23cc
2 changed files with 5 additions and 3 deletions
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1
pipelined/src/ifu/bpred/bpred.sv
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@ -149,6 +149,7 @@ module bpred (
.PredValidF,
.PredictionInstrClassWrongE,
.IEUAdrE,
.InstrClassD,
.InstrClassE);
// the branch predictor needs a compact decoding of the instruction class.

7
pipelined/src/ifu/bpred/btb.sv
View File

@ -41,6 +41,7 @@ module btb #(parameter int Depth = 10 ) (
// update
input logic PredictionInstrClassWrongE, // BTB's instruction class guess was wrong
input logic [`XLEN-1:0] IEUAdrE, // Branch/jump target address to insert into btb
input logic [3:0] InstrClassD, // Instruction class to insert into btb
input logic [3:0] InstrClassE // Instruction class to insert into btb
);
@ -71,7 +72,7 @@ module btb #(parameter int Depth = 10 ) (
assign ResetPC = `RESET_VECTOR;
assign PCNextFIndex = reset ? ResetPC[Depth+1:2] : {PCNextF[Depth+1] ^ PCNextF[1], PCNextF[Depth:2]};
assign MatchF = PCNextFIndex == PCFIndex;
assign MatchF = PCNextFIndex == PCFIndex & PredValidF;
assign MatchD = PCNextFIndex == PCDIndex;
assign MatchE = PCNextFIndex == PCEIndex;
assign MatchNextX = MatchF | MatchD | MatchE;
@ -79,7 +80,7 @@ module btb #(parameter int Depth = 10 ) (
flopenr #(1) MatchReg(clk, reset, ~StallF, MatchNextX, MatchXF);
assign ForwardBTBPrediction = MatchF ? {BTBPredInstrClassF, PredPCF} :
MatchD ? {PredInstrClassD, PredPCD} :
MatchD ? {InstrClassD, PredPCD} :
{InstrClassE, IEUAdrE} ;
flopenr #(`XLEN+4) ForwardBTBPredicitonReg(clk, reset, ~StallF, ForwardBTBPrediction, ForwardBTBPredictionF);
@ -104,6 +105,6 @@ module btb #(parameter int Depth = 10 ) (
.clk, .ce1(~StallF | reset), .ra1(PCNextFIndex), .rd1(TableBTBPredictionF),
.ce2(~StallM & ~FlushM), .wa2(PCEIndex), .wd2({InstrClassE, IEUAdrE}), .we2(UpdateEn), .bwe2('1));
flopenrc #(`XLEN+4) BTBD(clk, reset, FlushD, ~StallD, {BTBPredInstrClassF, PredPCF}, {PredInstrClassD, PredPCD});
flopenrc #(`XLEN) BTBD(clk, reset, FlushD, ~StallD, PredPCF, PredPCD);
endmodule