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Simiplified BTB.

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This commit is contained in:
Ross Thompson 2023-02-20 15:39:42 -06:00
parent 36b2d530c4
commit 545af7697f
4 changed files with 27 additions and 21 deletions
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10
src/ifu/bpred/bpred.sv
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@ -56,6 +56,7 @@ module bpred (
input logic JumpD, JumpE,
input logic PCSrcE, // Executation stage branch is taken
input logic [`XLEN-1:0] IEUAdrE, // The branch/jump target address
input logic [`XLEN-1:0] IEUAdrM, // The branch/jump target address
input logic [`XLEN-1:0] PCLinkE, // The address following the branch instruction. (AKA Fall through address)
output logic [3:0] InstrClassM, // The valid instruction class. 1-hot encoded as jalr, ret, jr (not ret), j, br
output logic JumpOrTakenBranchM, // The valid instruction class. 1-hot encoded as jalr, ret, jr (not ret), j, br
@ -143,14 +144,13 @@ module bpred (
// BTB contains target address for all CFI
btb #(`BTB_SIZE)
TargetPredictor(.clk, .reset, .StallF, .StallD, .StallM, .FlushD, .FlushM,
.PCNextF, .PCF, .PCD, .PCE,
TargetPredictor(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .FlushD, .FlushE, .FlushM,
.PCNextF, .PCF, .PCD, .PCE, .PCM,
.PredPCF,
.BTBPredInstrClassF,
.AnyWrongPredInstrClassE,
.IEUAdrE,
.InstrClassD,
.InstrClassE);
.IEUAdrE, .IEUAdrM,
.InstrClassD, .InstrClassE, .InstrClassM);
// the branch predictor needs a compact decoding of the instruction class.
if (`INSTR_CLASS_PRED == 0) begin : DirectClassDecode

33
src/ifu/bpred/btb.sv
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@ -31,22 +31,24 @@
`include "wally-config.vh"
module btb #(parameter Depth = 10 ) (
input logic clk,
input logic reset,
input logic StallF, StallD, StallM, FlushD, FlushM,
input logic [`XLEN-1:0] PCNextF, PCF, PCD, PCE, // PC at various stages
output logic [`XLEN-1:0] PredPCF, // BTB's guess at PC
output logic [3:0] BTBPredInstrClassF, // BTB's guess at instruction class
input logic clk,
input logic reset,
input logic StallF, StallD, StallE, StallM, FlushD, FlushE, FlushM,
input logic [`XLEN-1:0] PCNextF, PCF, PCD, PCE, PCM, // PC at various stages
output logic [`XLEN-1:0] PredPCF, // BTB's guess at PC
output logic [3:0] BTBPredInstrClassF, // BTB's guess at instruction class
// update
input logic AnyWrongPredInstrClassE, // 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
input logic AnyWrongPredInstrClassE, // BTB's instruction class guess was wrong
input logic [`XLEN-1:0] IEUAdrE, // Branch/jump target address to insert into btb
input logic [`XLEN-1:0] IEUAdrM, // 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
input logic [3:0] InstrClassM // Instruction class to insert into btb
);
logic [Depth-1:0] PCNextFIndex, PCFIndex, PCDIndex, PCEIndex;
logic [Depth-1:0] PCNextFIndex, PCFIndex, PCDIndex, PCEIndex, PCMIndex;
logic [`XLEN-1:0] ResetPC;
logic MatchF, MatchD, MatchE, MatchNextX, MatchXF;
logic MatchF, MatchD, MatchE, MatchM, MatchNextX, MatchXF;
logic [`XLEN+3:0] ForwardBTBPrediction, ForwardBTBPredictionF;
logic [`XLEN+3:0] TableBTBPredictionF;
logic [`XLEN-1:0] PredPCD;
@ -59,6 +61,7 @@ module btb #(parameter Depth = 10 ) (
assign PCFIndex = {PCF[Depth+1] ^ PCF[1], PCF[Depth:2]};
assign PCDIndex = {PCD[Depth+1] ^ PCD[1], PCD[Depth:2]};
assign PCEIndex = {PCE[Depth+1] ^ PCE[1], PCE[Depth:2]};
assign PCMIndex = {PCM[Depth+1] ^ PCM[1], PCM[Depth:2]};
// must output a valid PC and valid bit during reset. Because only PCF, not PCNextF is reset, PCNextF is invalid
// during reset. The BTB must produce a non X PC1NextF to allow the simulation to run.
@ -70,13 +73,15 @@ module btb #(parameter Depth = 10 ) (
assign MatchF = PCNextFIndex == PCFIndex;
assign MatchD = PCNextFIndex == PCDIndex;
assign MatchE = PCNextFIndex == PCEIndex;
assign MatchM = PCNextFIndex == PCMIndex;
assign MatchNextX = MatchF | MatchD | MatchE;
flopenr #(1) MatchReg(clk, reset, ~StallF, MatchNextX, MatchXF);
assign ForwardBTBPrediction = MatchF ? {BTBPredInstrClassF, PredPCF} :
MatchD ? {InstrClassD, PredPCD} :
{InstrClassE, IEUAdrE} ;
MatchE ? {InstrClassE, IEUAdrE} :
{InstrClassM, IEUAdrM} ;
flopenr #(`XLEN+4) ForwardBTBPredicitonReg(clk, reset, ~StallF, ForwardBTBPrediction, ForwardBTBPredictionF);
@ -90,6 +95,6 @@ module btb #(parameter Depth = 10 ) (
.clk, .ce1(~StallF | reset), .ra1(PCNextFIndex), .rd1(TableBTBPredictionF),
.ce2(~StallM & ~FlushM), .wa2(PCEIndex), .wd2({InstrClassE, IEUAdrE}), .we2(UpdateEn), .bwe2('1));
flopenrc #(`XLEN) BTBD(clk, reset, FlushD, ~StallD, {PredPCF}, {PredPCD});
flopenrc #(`XLEN) BTBD(clk, reset, FlushD, ~StallD, PredPCF, PredPCD);
endmodule

3
src/ifu/ifu.sv
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@ -52,6 +52,7 @@ module ifu (
output logic [`XLEN-1:0] PCLinkE, // The address following the branch instruction. (AKA Fall through address)
input logic PCSrcE, // Executation stage branch is taken
input logic [`XLEN-1:0] IEUAdrE, // The branch/jump target address
input logic [`XLEN-1:0] IEUAdrM, // The branch/jump target address
output logic [`XLEN-1:0] PCE, // Execution stage instruction address
output logic BPPredWrongE, // Prediction is wrong
output logic BPPredWrongM, // Prediction is wrong
@ -327,7 +328,7 @@ module ifu (
.StallF, .StallD, .StallE, .StallM, .StallW,
.FlushD, .FlushE, .FlushM, .FlushW, .InstrValidD, .InstrValidE,
.BranchD, .BranchE, .JumpD, .JumpE,
.InstrD, .PCNextF, .PCPlus2or4F, .PCNext1F, .PCE, .PCM, .PCSrcE, .IEUAdrE, .PCF, .NextValidPCE,
.InstrD, .PCNextF, .PCPlus2or4F, .PCNext1F, .PCE, .PCM, .PCSrcE, .IEUAdrE, .IEUAdrM, .PCF, .NextValidPCE,
.PCD, .PCLinkE, .InstrClassM, .BPPredWrongE, .PostSpillInstrRawF, .JumpOrTakenBranchM, .BPPredWrongM,
.DirPredictionWrongM, .BTBPredPCWrongM, .RASPredPCWrongM, .PredictionInstrClassWrongM);

2
src/wally/wallypipelinedcore.sv
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@ -174,7 +174,7 @@ module wallypipelinedcore (
.IFUStallF, .IFUHBURST, .IFUHTRANS, .IFUHSIZE, .IFUHREADY, .IFUHWRITE,
.ICacheAccess, .ICacheMiss,
// Execute
.PCLinkE, .PCSrcE, .IEUAdrE, .PCE, .BPPredWrongE, .BPPredWrongM,
.PCLinkE, .PCSrcE, .IEUAdrE, .IEUAdrM, .PCE, .BPPredWrongE, .BPPredWrongM,
// Mem
.CommittedF, .UnalignedPCNextF, .InvalidateICacheM, .CSRWriteFenceM,
.InstrD, .InstrM, .PCM, .InstrClassM, .DirPredictionWrongM, .JumpOrTakenBranchM,