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Simplified SLT and SLTU code in ALU

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David Harris 2023-03-09 15:14:52 -08:00
parent 9a6514f20d
commit 2614448218
1 changed files with 10 additions and 14 deletions
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24
src/ieu/alu.sv
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@ -38,7 +38,7 @@ module alu #(parameter WIDTH=32) (
// CondInvB = ~B when subtracting, B otherwise. Shift = shift result. SLT/U = result of a slt/u instruction.
// FullResult = ALU result before adjusting for a RV64 w-suffix instruction.
logic [WIDTH-1:0] CondInvB, Shift, SLT, SLTU, FullResult; // Intermediate results
logic [WIDTH-1:0] CondInvB, Shift, FullResult; // Intermediate results
logic Carry, Neg; // Flags: carry out, negative
logic LT, LTU; // Less than, Less than unsigned
logic W64; // RV64 W-type instruction
@ -66,21 +66,17 @@ module alu #(parameter WIDTH=32) (
assign LT = Asign & ~Bsign | Asign & Neg | ~Bsign & Neg;
assign LTU = ~Carry;
// SLT
assign SLT = {{(WIDTH-1){1'b0}}, LT};
assign SLTU = {{(WIDTH-1){1'b0}}, LTU};
// Select appropriate ALU Result
always_comb
if (~ALUOp) FullResult = Sum; // Always add for ALUOp = 0 (address generation)
else casez (Funct3) // Otherwise check Funct3
3'b000: FullResult = Sum; // add or sub
3'b?01: FullResult = Shift; // sll, sra, or srl
3'b010: FullResult = SLT; // slt
3'b011: FullResult = SLTU; // sltu
3'b100: FullResult = A ^ B; // xor
3'b110: FullResult = A | B; // or
3'b111: FullResult = A & B; // and
if (~ALUOp) FullResult = Sum; // Always add for ALUOp = 0 (address generation)
else casez (Funct3) // Otherwise check Funct3
3'b000: FullResult = Sum; // add or sub
3'b?01: FullResult = Shift; // sll, sra, or srl
3'b010: FullResult = {{(WIDTH-1){1'b0}}, LT}; // slt
3'b011: FullResult = {{(WIDTH-1){1'b0}}, LTU}; // sltu
3'b100: FullResult = A ^ B; // xor
3'b110: FullResult = A | B; // or
3'b111: FullResult = A & B; // and
endcase
// Support RV64I W-type addw/subw/addiw/shifts that discard upper 32 bits and sign-extend 32-bit result to 64 bits