16 -bit CLA instantiation - verilog

Question

DO I need anything else to make a 16bit CLA ??????
so far I instantiated 4 (4 bit CLA to make a 16 bit CLA)
but I think I am missing about the carry I just don't understand how to add it to what I have since the 8 bit CLA was just instantiating 2 (4 bit CLA) I don't understand why can't just instantiate 4 (4 bit CLA together to get 16 bit CLA). Can someone help me figure out how to complete the 16bit CLA?
//CLA16Top.sv
module CLA4Bit(ain, bin, cin, sum, cout);
timeunit 1ns/1ns;
input [3:0] ain,bin;
input cin;
output logic [3:0] sum;
output logic cout;
logic [3:0] G,P,C;
// Carry propagate
assign P = ain ^ bin;
//Carry generate
assign G = ain & bin;
// Calculating each stage of the carry out
assign C[0] = cin;
assign #4 C[1] = (G[0] | (C[0] & P[0]));
assign #6 C[2] = (G[1] | (G[0] & P[1]) | (C[0] & P[1] & P[0]));
assign #8 C[3] = (G[2] | (G[1] & P[2]) | (G[0] & P[1] & P[2]) | (C[0] &
P[2] & P[1] & P[0]));
assign sum = P ^ C;
assign #13 cout= (G[3] | (G[2]&P[3]) | (G[1]&P[2]&P[3]) |
(G[0]&P[1]&P[2]&P[3]) | (C[0]&P[0]&P[1]&P[2]&P[3]));
endmodule
/*
module CLA16Top;
timeunit 1ns/1ns;
parameter nBITS = 16;
logic [nBITS - 1 : 0] ain, bin, sum;
logic in;
logic cout;
logic c4, c8, c12, c16;
assign cout = c16;
// instantiating the 16 bit CLA
CLA4Bit uut1(
.ain(ain[3:0]),
.bin(bin[3:0]),
.cin(cin),
.sum(sum[3:0]),
.cout(c4)
);
CLA4Bit uut2(
.ain(ain[7:4]),
.bin(bin[7:4]),
.cin(c4),
.sum(sum[7:4]),
.cout(c8)
);
CLA4Bit uut3(
.ain(ain[11:8]),
.bin(bin[11:8]),
.cin(c8),
.sum(sum[11:8]),
.cout(c12)
);
CLA4Bit uut4(
.ain(ain[15:12]),
.bin(bin[15:12]),
.cin(c12),
.sum(sum[15:12]),
.cout(c16)
);
// SIMULATE (CLA16Top)
//
test #(16) TB(.*);
endmodule: CLA16Top

Answer 1

I get compile errors in your test module. Change:
output in;
to:
output cin;
Also, the double-quoted string must be on one line:
$display("For inputs: ain = %b, bin = %b, cin = %b :: Actual outputs: cout = %1b, sum = %b :: Expected outputs: cout = %1b, sum = %b", ain, bin, cin, cout,
test_count could be too big to fit into an int variable. Use real and %g:
real test_count;
$display("***Congratulations, No errors found after %g tests***", test_count);
After those changes, the code compiles and runs for me. It took about 2 hours before the nested loops completed, and only the final message displays:
***Congratulations, No errors found after 8.58993e+09 tests***
This indicates that the adder works properly.
If you want to see more intermediate results, add more displays in the loops.
Note: The test module code was removed from the Question after I posted this Answer.