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Cleaned up branch predictor.

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This commit is contained in:
Ross Thompson 2023-01-25 15:29:55 -06:00
parent bb89bf82bf
commit 3d285312f0
2 changed files with 7 additions and 10 deletions
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3
pipelined/src/ifu/brpred/bpred.sv
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@ -142,8 +142,7 @@ module bpred (
.BTBPredPCF, .BTBPredPCF,
.PredInstrClassF, .PredInstrClassF,
.PredValidF, .PredValidF,
// update .PredictionInstrClassWrongE,
.UpdateEN(|InstrClassE | PredictionInstrClassWrongE),
.PCE, .PCE,
.IEUAdrE, .IEUAdrE,
.InstrClassE); .InstrClassE);

14
pipelined/src/ifu/brpred/btb.sv
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@ -41,7 +41,7 @@ module btb
output logic [3:0] PredInstrClassF, output logic [3:0] PredInstrClassF,
output logic PredValidF, output logic PredValidF,
// update // update
input logic UpdateEN, input logic PredictionInstrClassWrongE,
input logic [`XLEN-1:0] PCE, input logic [`XLEN-1:0] PCE,
input logic [`XLEN-1:0] IEUAdrE, input logic [`XLEN-1:0] IEUAdrE,
input logic [3:0] InstrClassE input logic [3:0] InstrClassE
@ -50,7 +50,6 @@ module btb
localparam TotalDepth = 2 ** Depth; localparam TotalDepth = 2 ** Depth;
logic [TotalDepth-1:0] ValidBits; logic [TotalDepth-1:0] ValidBits;
logic [Depth-1:0] PCNextFIndex, PCFIndex, PCDIndex, PCEIndex; logic [Depth-1:0] PCNextFIndex, PCFIndex, PCDIndex, PCEIndex;
logic UpdateENQ;
logic [`XLEN-1:0] ResetPC; logic [`XLEN-1:0] ResetPC;
logic MatchF, MatchD, MatchE, MatchNextX, MatchXF; logic MatchF, MatchD, MatchE, MatchNextX, MatchXF;
logic [`XLEN+3:0] ForwardBTBPrediction, ForwardBTBPredictionF; logic [`XLEN+3:0] ForwardBTBPrediction, ForwardBTBPredictionF;
@ -67,8 +66,10 @@ module btb
assign PCDIndex = {PCD[Depth+1] ^ PCD[1], PCD[Depth:2]}; assign PCDIndex = {PCD[Depth+1] ^ PCD[1], PCD[Depth:2]};
assign PCEIndex = {PCE[Depth+1] ^ PCE[1], PCE[Depth:2]}; assign PCEIndex = {PCE[Depth+1] ^ PCE[1], PCE[Depth:2]};
// must output a valid PC and valid bit during reset. Because the PCNextF logic of the IFU and trap units // must output a valid PC and valid bit during reset. Because only PCF, not PCNextF is reset, PCNextF is invalid
// does not mux in RESET_VECTOR we have to do it here. This is a performance optimization. // during reset. The BTB must produce a non X PC1NextF to allow the simulation to run.
// While thie mux could be included in IFU it is not necessary for the IROM/I$/bus.
// For now it is optimal to leave it here.
assign ResetPC = `RESET_VECTOR; assign ResetPC = `RESET_VECTOR;
assign PCNextFIndex = reset ? ResetPC[Depth+1:2] : {PCNextF[Depth+1] ^ PCNextF[1], PCNextF[Depth:2]}; assign PCNextFIndex = reset ? ResetPC[Depth+1:2] : {PCNextF[Depth+1] ^ PCNextF[1], PCNextF[Depth:2]};
@ -90,7 +91,7 @@ module btb
always_ff @ (posedge clk) begin always_ff @ (posedge clk) begin
if (reset) begin if (reset) begin
ValidBits <= #1 {TotalDepth{1'b0}}; ValidBits <= #1 {TotalDepth{1'b0}};
end else if (UpdateEN & ~StallM & ~FlushM) begin end else if ((|InstrClassE | PredictionInstrClassWrongE) & ~StallM & ~FlushM) begin
ValidBits[PCEIndex] <= #1 |InstrClassE; ValidBits[PCEIndex] <= #1 |InstrClassE;
end end
PredValidF = ValidBits[PCNextFIndex]; PredValidF = ValidBits[PCNextFIndex];
@ -103,7 +104,4 @@ module btb
flopenrc #(`XLEN+4) BTBD(clk, reset, FlushD, ~StallD, {PredInstrClassF, BTBPredPCF}, {PredInstrClassD, BTBPredPCD}); flopenrc #(`XLEN+4) BTBD(clk, reset, FlushD, ~StallD, {PredInstrClassF, BTBPredPCF}, {PredInstrClassD, BTBPredPCD});
endmodule endmodule