65. Ripple Carry Adder

How do you plan to solve it?

// 1-bit Full Adder (to be used by the 4-bit RCA)
module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);
    wire sum1, carry1, carry2;

    // First half adder
    xor(sum1, a , b);
    and(carry1, a, b);

    // Second half adder
    xor(sum, sum1, cin);
    and(carry2, sum1, cin);

    // Compute output carry
    or(cout, carry1, carry2);
endmodule

// 4-bit Ripple Carry Adder chain 4 full adders
module rca4_chain (
    input  [3:0] a,
    input  [3:0] b,
    input        cin,
    output [3:0] sum,
    output       cout
);
    // TODO: Declare internal ripple carries
    wire carry1, carry2, carry3;

    // TODO: instantiate 4 full adders and chain carries
    full_adder_1bit add0(
        .a(a[0]),
        .b(b[0]),
        .cin(cin),
        .sum(sum[0]),
        .cout(carry1)
    );
    full_adder_1bit add1(
        .a(a[1]),
        .b(b[1]),
        .cin(carry1),
        .sum(sum[1]),
        .cout(carry2)
    );
    full_adder_1bit add2(
        .a(a[2]),
        .b(b[2]),
        .cin(carry2),
        .sum(sum[2]),
        .cout(carry3)
    );
    full_adder_1bit add3(
        .a(a[3]),
        .b(b[3]),
        .cin(carry3),
        .sum(sum[3]),
        .cout(cout)
    );

    // TODO: drive cout


endmodule