Alu Control output not return 010 for Addi instruction

Question

I'm currently working on a project for a MIPS Datapath Simulation website. The project aims to demonstrate how instructions work. I've implemented the Alu Control Unit using the combinational logic shown in this image:

I'm facing an issue with the addi instruction. While the AluOp is set to 11 for addi, since it's an I-type instruction, the func bits are X (don't care). However, the current logic doesn't allow for overwriting in this case. Do I need to modify this component for addi instruction? I've been searching for the past 3-4 days, but I haven't come across any specific implementations for I-type instructions.

By the way, I'm primarily a software developer and I'm trying to gain a better understanding of MIPS CPU design. Any additional resources or references you could provide would be greatly appreciated.

For anyone who wants to try the simulation, here is the current demo: https://saliherdemk.github.io/Mips-Datapath-Simulator/

Answer 1

I didn't find any circuit for this so I ended up with this design.

It works for add, sub, and, or, jr, addi, lw, sw, beq, j and jal instructions.

And here is the js implementation

  let a1 = aluop0 && aluop1;
  let a2 = (f1 && aluop1) || aluop0;

  let op2 = a1 ^ a2; // (!a1 && a2) || (!a2 && a1)
  let op1 = !f2 || !aluop1 || a1;
  let op0 = (f0 || f3) && aluop1 && !aluop0;