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Reorganized IFU PCNextF logic.

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This commit is contained in:
Ross Thompson 2022-12-20 12:58:54 -06:00
parent 16f3c25cb7
commit 684d260005
3 changed files with 48 additions and 48 deletions
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31
pipelined/src/ifu/bpred.sv
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@ -43,7 +43,6 @@ module bpred
input logic [`XLEN-1:0] PCNextF, // *** forgot to include this one on the I/O list
input logic [`XLEN-1:0] PCPlus2or4F,
output logic [`XLEN-1:0] PCNext1F,
output logic [`XLEN-1:0] PCCorrectE,
output logic [`XLEN-1:0] NextValidPCE, // The address of the currently executing instruction
// Update Predictor
@ -84,13 +83,10 @@ module bpred
logic [`XLEN-1:0] BPPredPCF;
logic BPPredWrongM;
logic [`XLEN-1:0] PCNext0F;
logic [`XLEN-1:0] PCCorrectE;
// Part 1 branch direction prediction
// look into the 2 port Sram model. something is wrong.
if (`BPTYPE == "BPTWOBIT") begin:Predictor
twoBitPredictor DirPredictor(.clk, .reset, .StallF,
.LookUpPC(PCNextF),
@ -263,23 +259,28 @@ module bpred
.NewState(UpdateBPPredE));
// Selects the BP or PC+2/4.
mux2 #(`XLEN) pcmux0(.d0(PCPlus2or4F), .d1(BPPredPCF), .s(SelBPPredF), .y(PCNext0F));
// If the prediction is wrong select the correct address.
mux2 #(`XLEN) pcmux1(.d0(PCNext0F), .d1(PCCorrectE), .s(BPPredWrongE), .y(PCNext1F));
// Correct branch/jump target.
mux2 #(`XLEN) pccorrectemux(.d0(PCLinkE), .d1(IEUAdrE), .s(PCSrcE), .y(PCCorrectE));
// If the fence/csrw was predicted as a taken branch then we select PCF, rather PCE.
// could also just use PCM+4, which should be pclinke
mux2 #(`XLEN) pcmuxBPWrongInvalidateFlush(.d0(PCE), .d1(PCF), .s(BPPredWrongM), .y(NextValidPCE));
// could also just use PCM+4, or PCLinkM
// ONLY valid for class prediction. add option for class prediction.
// if(`BPCLASS) begin
mux2 #(`XLEN) pcmuxBPWrongInvalidateFlush(.d0(PCE), .d1(PCF), .s(BPPredWrongM), .y(NextValidPCE));
// end else begin
// assign NextValidPCE = PCE;
// end
//logic [`XLEN-1:0] PCLinkM;
//flopenr #(`XLEN) PCPEReg(clk, reset, ~StallM, PCLinkE, PCLinkM);
//assign NextValidPCE = PCLinkM;
// of the three, the mux is the cheapest, but the least clear.
// this could move entirely into ifu with no relation to bp with the third.
//assign NextValidPCE = PCE;
mux2 #(`XLEN) pcmux1(.d0(PCNext0F), .d1(PCCorrectE), .s(BPPredWrongE), .y(PCNext1F));
endmodule

56
pipelined/src/ifu/ifu.sv
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@ -85,9 +85,8 @@ module ifu (
output logic ICacheAccess,
output logic ICacheMiss
);
(* mark_debug = "true" *) logic [`XLEN-1:0] PCCorrectE, UnalignedPCNextF, PCNextF;
(* mark_debug = "true" *) logic [`XLEN-1:0] UnalignedPCNextF, PCNextF;
logic BranchMisalignedFaultE;
logic PrivilegedChangePCM;
logic IllegalCompInstrD;
logic [`XLEN-1:0] PCPlus2or4F, PCLinkD;
logic [`XLEN-3:0] PCPlusUpperF;
@ -286,41 +285,19 @@ module ifu (
// PCNextF logic
////////////////////////////////////////////////////////////////////////////////////////////////
assign PrivilegedChangePCM = RetM | TrapM;
// if(`ICACHE | `ZICSR_SUPPORTED)
mux2 #(`XLEN) pcmux2(.d0(PCNext1F), .d1(NextValidPCE), .s(CSRWriteFenceM),.y(PCNext2F));
// mux2 #(`XLEN) pcmux2(.d0(PCNext1F), .d1(PCM+4), .s(CSRWriteFenceM),.y(PCNext2F));
// else assign PCNext2F = PCNext1F;
if(`ZICSR_SUPPORTED)
if(`ZICSR_SUPPORTED) begin
logic PrivilegedChangePCM;
assign PrivilegedChangePCM = RetM | TrapM;
mux2 #(`XLEN) pcmux3(.d0(PCNext2F), .d1(PrivilegedNextPCM), .s(PrivilegedChangePCM),
.y(UnalignedPCNextF));
else assign UnalignedPCNextF = PCNext2F;
.y(UnalignedPCNextF));
end else assign UnalignedPCNextF = PCNext2F;
assign PCNextF = {UnalignedPCNextF[`XLEN-1:1], 1'b0}; // hart-SPEC p. 21 about 16-bit alignment
flopenl #(`XLEN) pcreg(clk, reset, ~StallF, PCNextF, `RESET_VECTOR, PCF);
////////////////////////////////////////////////////////////////////////////////////////////////
// Branch and Jump Predictor
////////////////////////////////////////////////////////////////////////////////////////////////
if (`BPRED_ENABLED) begin : bpred
bpred bpred(.clk, .reset,
.StallF, .StallD, .StallE, .StallM,
.FlushD, .FlushE, .FlushM,
.InstrD, .PCNextF, .PCPlus2or4F, .PCNext1F, .PCE, .PCSrcE, .IEUAdrE, .PCCorrectE, .PCF, .NextValidPCE,
.PCD, .PCLinkE, .InstrClassM, .BPPredWrongE,
.BPPredDirWrongM, .BTBPredPCWrongM, .RASPredPCWrongM, .BPPredClassNonCFIWrongM);
end else begin : bpred
mux2 #(`XLEN) pcmux1(.d0(PCPlus2or4F), .d1(IEUAdrE), .s(PCSrcE), .y(PCNext1F));
assign BPPredWrongE = PCSrcE;
assign {BPPredDirWrongM, BTBPredPCWrongM, RASPredPCWrongM, BPPredClassNonCFIWrongM} = '0;
assign PCNext0F = PCPlus2or4F;
assign PCCorrectE = IEUAdrE;
assign NextValidPCE = PCE;
end
// pcadder
// add 2 or 4 to the PC, based on whether the instruction is 16 bits or 32
assign PCPlusUpperF = PCF[`XLEN-1:2] + 1; // add 4 to PC
@ -334,6 +311,27 @@ module ifu (
else PCPlus2or4F = {PCF[`XLEN-1:2], 2'b10};
else PCPlus2or4F = {PCPlusUpperF, PCF[1:0]}; // add 4
////////////////////////////////////////////////////////////////////////////////////////////////
// Branch and Jump Predictor
////////////////////////////////////////////////////////////////////////////////////////////////
if (`BPRED_ENABLED) begin : bpred
bpred bpred(.clk, .reset,
.StallF, .StallD, .StallE, .StallM,
.FlushD, .FlushE, .FlushM,
.InstrD, .PCNextF, .PCPlus2or4F, .PCNext1F, .PCE, .PCSrcE, .IEUAdrE, .PCF, .NextValidPCE,
.PCD, .PCLinkE, .InstrClassM, .BPPredWrongE,
.BPPredDirWrongM, .BTBPredPCWrongM, .RASPredPCWrongM, .BPPredClassNonCFIWrongM);
end else begin : bpred
mux2 #(`XLEN) pcmux1(.d0(PCPlus2or4F), .d1(IEUAdrE), .s(PCSrcE), .y(PCNext1F));
assign BPPredWrongE = PCSrcE;
assign {BPPredDirWrongM, BTBPredPCWrongM, RASPredPCWrongM, BPPredClassNonCFIWrongM} = '0;
assign PCNext0F = PCPlus2or4F;
assign NextValidPCE = PCE;
end
////////////////////////////////////////////////////////////////////////////////////////////////
// Decode stage pipeline register and compressed instruction decoding.
////////////////////////////////////////////////////////////////////////////////////////////////

9
pipelined/src/ifu/spillsupport.sv
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@ -59,10 +59,11 @@ module spillsupport #(parameter CACHE_ENABLED)
typedef enum logic [1:0] {STATE_READY, STATE_SPILL} statetype;
(* mark_debug = "true" *) statetype CurrState, NextState;
mux2 #(`XLEN) pcplus2mux(.d0({PCF[`XLEN-1:2], 2'b10}), .d1({PCPlusUpperF, 2'b00}),
.s(PCF[1]), .y(PCPlus2F));
mux2 #(`XLEN) pcnextspillmux(.d0(PCNextF), .d1(PCPlus2F), .s(SelNextSpillF & ~Flush),
.y(PCNextFSpill));
// compute PCF+2
mux2 #(`XLEN) pcplus2mux(.d0({PCF[`XLEN-1:2], 2'b10}), .d1({PCPlusUpperF, 2'b00}), .s(PCF[1]), .y(PCPlus2F));
// select between PCNextF and PCF+2
mux2 #(`XLEN) pcnextspillmux(.d0(PCNextF), .d1(PCPlus2F), .s(SelNextSpillF & ~Flush), .y(PCNextFSpill));
// select between PCF adn PCF+2
mux2 #(`XLEN) pcspillmux(.d0(PCF), .d1(PCPlus2F), .s(SelSpillF), .y(PCFSpill));
assign SpillF = &PCF[$clog2(SPILLTHRESHOLD)+1:1];