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ALUControl cleanup

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This commit is contained in:
David Harris 2021-12-19 13:53:45 -08:00
parent f201af4bb7
commit 9e6c9c38c0
1 changed files with 3 additions and 4 deletions
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wally-pipelined/src/ieu/controller.sv
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@ -170,10 +170,10 @@ module controller(
assign CSRZeroSrcD = InstrD[14] ? (InstrD[19:15] == 0) : (Rs1D == 0); // Is a CSR instruction using zero as the source? assign CSRZeroSrcD = InstrD[14] ? (InstrD[19:15] == 0) : (Rs1D == 0); // Is a CSR instruction using zero as the source?
assign CSRWriteD = CSRReadD & !(CSRZeroSrcD && InstrD[13]); // Don't write if setting or clearing zeros assign CSRWriteD = CSRReadD & !(CSRZeroSrcD && InstrD[13]); // Don't write if setting or clearing zeros
// ALU Decoding // ALU Decoding is lazy, only using func7[5] to distinguish add/sub and srl/sra
assign sltD = (Funct3D == 3'b010); assign sltD = (Funct3D == 3'b010);
assign sltuD = (Funct3D == 3'b011); assign sltuD = (Funct3D == 3'b011);
assign subD = (Funct3D == 3'b000 & Funct7D[5] & OpD[5]); // OpD[5] needed; ***explain why assign subD = (Funct3D == 3'b000 & Funct7D[5] & OpD[5]); // OpD[5] needed to distinguish sub from addi
assign sraD = (Funct3D == 3'b101 & Funct7D[5]); assign sraD = (Funct3D == 3'b101 & Funct7D[5]);
assign SubArithD = ALUOpD & (subD | sraD | sltD | sltuD); // TRUE for R-type subtracts and sra, slt, sltu assign SubArithD = ALUOpD & (subD | sraD | sltD | sltuD); // TRUE for R-type subtracts and sra, slt, sltu
assign ALUControlD = {W64D, SubArithD, ALUOpD}; assign ALUControlD = {W64D, SubArithD, ALUOpD};
@ -205,12 +205,11 @@ module controller(
assign {eqE, ltE, ltuE} = FlagsE; assign {eqE, ltE, ltuE} = FlagsE;
mux4 #(1) branchflagmux(eqE, 1'b0, ltE, ltuE, Funct3E[2:1], BranchFlagE); mux4 #(1) branchflagmux(eqE, 1'b0, ltE, ltuE, Funct3E[2:1], BranchFlagE);
assign BranchTakenE = BranchFlagE ^ Funct3E[0]; assign BranchTakenE = BranchFlagE ^ Funct3E[0];
assign PCSrcE = JumpE | BranchE & BranchTakenE; assign PCSrcE = JumpE | BranchE & BranchTakenE;
// Other execute stage controller signals
assign MemReadE = MemRWE[1]; assign MemReadE = MemRWE[1];
assign SCE = (ResultSrcE == 3'b100); assign SCE = (ResultSrcE == 3'b100);
assign RegWriteE = IEURegWriteE | FWriteIntE; // IRF register writes could come from IEU or FPU controllers assign RegWriteE = IEURegWriteE | FWriteIntE; // IRF register writes could come from IEU or FPU controllers
// Memory stage pipeline control register // Memory stage pipeline control register