1 files changed, 43 insertions, 0 deletions
diff --git a/rtl/src/alu_op_decode.v b/rtl/src/alu_op_decode.v
new file mode 100644
index 0000000..4523255
--- /dev/null
+++ b/rtl/src/alu_op_decode.v
@@ -0,0 +1,43 @@
+module alu_op_decode (
+  input [6:0] opcode,
+  input [2:0] funct3,
+  input [6:0] funct7,
+  
+  input alu_ctrl,
+  
+  output reg [3:0] alu_op
+);
+
+`include "include/consts.vh"
+
+always @ (*) begin
+  if (alu_ctrl == ALU_CTRL_ADD) begin
+    alu_op = ALU_OP_ADD;
+  end else if (opcode == OPCODE_REG || opcode == OPCODE_IMM) begin
+    case (funct3)
+      FUNCT3_ALU_ADD_SUB: alu_op = (opcode == OPCODE_REG && funct7 == FUNCT7_ALU_SUB) ? ALU_OP_SUB : ALU_OP_ADD;
+      FUNCT3_ALU_SLL:     alu_op = ALU_OP_SLL;
+      FUNCT3_ALU_SLT:     alu_op = ALU_OP_SLT;
+      FUNCT3_ALU_SLTU:    alu_op = ALU_OP_SLTU;
+      FUNCT3_ALU_XOR:     alu_op = ALU_OP_XOR;
+      FUNCT3_ALU_SR:      alu_op = funct7 == FUNCT7_ALU_SRL ? ALU_OP_SRL : ALU_OP_SRA;
+      FUNCT3_ALU_OR:      alu_op = ALU_OP_OR;
+      FUNCT3_ALU_AND:     alu_op = ALU_OP_AND;
+      default:            alu_op = ALU_OP_ADD;
+    endcase
+  end else if (opcode == OPCODE_BRANCH) begin
+    case (funct3)
+      FUNCT3_BRANCH_BEQ:  alu_op = ALU_OP_SUB;
+      FUNCT3_BRANCH_BNE:  alu_op = ALU_OP_SUB;
+      FUNCT3_BRANCH_BLT:  alu_op = ALU_OP_SLT;
+      FUNCT3_BRANCH_BGE:  alu_op = ALU_OP_SLT;
+      FUNCT3_BRANCH_BLTU: alu_op = ALU_OP_SLTU;
+      FUNCT3_BRANCH_BGEU: alu_op = ALU_OP_SLTU;
+      default:            alu_op = ALU_OP_ADD;
+    endcase
+  end else begin
+    alu_op = ALU_OP_ADD;
+  end
+end
+
+endmodule