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Removed unnecessary pc reset logic from ifu and btb.

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This commit is contained in:
Rose Thompson 2023-12-13 13:05:10 -06:00
parent c6ed08ce12
commit c98c0dd3e0
2 changed files with 4 additions and 11 deletions
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8
src/ifu/bpred/btb.sv
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@ -50,7 +50,6 @@ module btb import cvw::*; #(parameter cvw_t P,
);
logic [Depth-1:0] PCNextFIndex, PCFIndex, PCDIndex, PCEIndex, PCMIndex, PCWIndex;
logic [P.XLEN-1:0] ResetPC;
logic MatchD, MatchE, MatchM, MatchW, MatchX;
logic [P.XLEN+3:0] ForwardBTBPrediction, ForwardBTBPredictionF;
logic [P.XLEN+3:0] TableBTBPredF;
@ -70,12 +69,7 @@ module btb import cvw::*; #(parameter cvw_t P,
assign PCMIndex = {PCM[Depth+1] ^ PCM[1], PCM[Depth:2]};
assign PCWIndex = {PCW[Depth+1] ^ PCW[1], PCW[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.
// While the 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 = P.RESET_VECTOR[P.XLEN-1:0];
assign PCNextFIndex = reset ? ResetPC[Depth+1:2] : {PCNextF[Depth+1] ^ PCNextF[1], PCNextF[Depth:2]};
assign PCNextFIndex = {PCNextF[Depth+1] ^ PCNextF[1], PCNextF[Depth:2]};
assign MatchD = PCFIndex == PCDIndex;
assign MatchE = PCFIndex == PCEIndex;

7
src/ifu/ifu.sv
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@ -300,8 +300,8 @@ module ifu import cvw::*; #(parameter cvw_t P) (
mux2 #(P.XLEN) pcmux2(.d0(PC1NextF), .d1(NextValidPCE), .s(CSRWriteFenceM),.y(PC2NextF));
else assign PC2NextF = PC1NextF;
assign PCNextF = {UnalignedPCNextF[P.XLEN-1:1], 1'b0}; // hart-SPEC p. 21 about 16-bit alignment
flopenl #(P.XLEN) pcreg(clk, reset, ~StallF, PCNextF, P.RESET_VECTOR[P.XLEN-1:0], PCF);
mux2 #(P.XLEN) pcresetmux({UnalignedPCNextF[P.XLEN-1:1], 1'b0}, P.RESET_VECTOR[P.XLEN-1:0], reset, PCNextF);
flopen #(P.XLEN) pcreg(clk, ~StallF | reset, PCNextF, PCF);
// pcadder
// add 2 or 4 to the PC, based on whether the instruction is 16 bits or 32
@ -315,8 +315,7 @@ module ifu import cvw::*; #(parameter cvw_t P) (
// an X. This version of the code does not die because if CompressedF is an X it just defaults to the last
// option. The above code would work, but propagates the x.
always_comb
if(reset) PCPlus2or4F = '0;
else if (CompressedF) // add 2
if (CompressedF) // add 2
if (PCF[1]) PCPlus2or4F = {PCPlus4F, 2'b00};
else PCPlus2or4F = {PCF[P.XLEN-1:2], 2'b10};
else PCPlus2or4F = {PCPlus4F, PCF[1:0]}; // add 4