65. Ripple Carry Adder

How do you plan to solve it?

// 1-bit Full Adder (to be used by the 4-bit RCA)
// Half Adder primitive
module half_adder (
    input  a, b,
    output sum, carry
);
    // Write code here
    assign sum   = a ^ b;
    assign carry = a & b;
endmodule

module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);
    // TODO: implement 1-bit full adder (structural or dataflow)
    wire sum1, carry1, carry2;
    // Write code here
    half_adder ha1 (.a(a),    .b(b),   .sum(sum1), .carry(carry1));
    half_adder ha2 (.a(sum1), .b(cin), .sum(sum), .carry(carry2));
    assign 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
    parameter BIT = 4;
	wire [BIT-1 : 0] c_out;
    // TODO: instantiate 4 full adders and chain carries
	full_adder_1bit fa0 (.a(a[0]),  .b(b[0]),  .cin(cin),      .sum(sum[0]),  .cout(c_out[0]));
	full_adder_1bit fa1 (.a(a[1]),  .b(b[1]),  .cin(c_out[0]),  .sum(sum[1]),  .cout(c_out[1]));
	full_adder_1bit fa2 (.a(a[2]),  .b(b[2]),  .cin(c_out[1]),  .sum(sum[2]),  .cout(c_out[2]));
	full_adder_1bit fa3 (.a(a[3]),  .b(b[3]),  .cin(c_out[2]),  .sum(sum[3]),  .cout(cout));

    // TODO: drive cout


endmodule