**LAB 9**

**Question 1**

module alu(res,op,a,b);
    input [3:0] a,b;
    input [1:0] op;
    output reg [3:0] res;
    always@(a or b or op or res)
        begin
            case(op)
                2'b00: res = a + b;
                2'b01: res = a - b;
                2'b10: res = a & b;
                2'b11: res = a | b;
                default: res = 4'b0000;
            endcase
        end
endmodule

module mux4to1(out1,in0,in1,in2,in3,sel);
    input [3:0] in0,in1,in2,in3;
    input [1:0] sel;
    output reg [3:0] out1;
    always@(in0 or in1 or in2 or in3 or sel)
        begin
            case(sel)
                2'b00: out1 = in0;
                2'b01: out1 = in1;
                2'b10: out1 = in2;
                2'b11: out1 = in3;
                default: out1 = 4'b0000;
            endcase
        end
endmodule

//test bench

module testbench;
    reg [3:0] a,b;
    reg [1:0] opcode;
    wire [3:0] result,out;
    
    alu at(.res(result),.op(opcode),.a(a),.b(b));
    
    mux4to1 m(.out1(out),.in0(4'b0000),.in1(4'b0000),.in2(4'b0000),.in3(result),.sel(opcode));
    
    initial
        begin
            a = 4'b1100; b = 4'b0011; opcode = 2'b00; #10;
            a = 4'b0111; b = 4'b0000; opcode = 2'b01; #10;
            a = 4'b0100; b = 4'b1111; opcode = 2'b10; #10;
            a = 4'b0010; b = 4'b1001; opcode = 2'b11; #10;
        end
endmodule


**Question 2**

module processor(input [7:0] inst);
    reg [7:0] memory [255:0];
    reg [7:0] regf [15:0];
    reg op;
    reg [1:0] destination;
    reg [2:0] offset;
    reg [1:0] src;
    
    always@(*)
        begin
            op = inst[7];
            destination = inst[6:5];
            offset = inst[4:2];
            src = inst[1:0];
        end
    always@(*)
        begin
            if(op == 0)
                begin
                    regf[destination] <= memory[regf[src]+offset];
                end
        end
    always@(*)
        begin
            if(op == 1)
                begin
                    memory[regf[src]+offset] <= regf[destination];
                end
        end
endmodule


**Question 3**

#include <stdio.h>

int main() {
    int a = 5;
    int b = 6;
    int c = a + b;
    printf("c = %d\n", c);

    return 0;
}