Programming Assignment PA5: CS 270 Computer Organization

Programming Assignment PA5 - Simulating Digital Logic

Programming due Sunday, Oct. 5 at 10:00pm, no late submission.

This assignment has three objectives:

To learn how to simulate digital logic with C functions,
to learn how to write unit tests in C using asserts,
and to increase your understanding of circuits that are fundamental to computer hardware.

About the Assignment

For this assignment you will write a C program to simulate gates, latches, decoders, multiplexers, and an adder. You need to submit a tar archive with the code files: main.c, logic.h, and logic.c. The Makefile will have a target to make the archive by typing:

$ make package

The logic.h and logic.c files already contain declarations, implementations, and the main program contains a unit test for each of the following functions:

    // Gates
    BIT or_gate(BIT A, BIT B);
    BIT not_gate(BIT A);

    // Sequential Circuits
    BIT rs_latch(BIT S, BIT R);

The header file also defines a BIT as an enumerated value. Add the functions shown below to the logic.c file, and corresponding tests to the main.c program. Note that O1 and O2 inputs to the adder function are 4-bits and unsigned, so you only need to worry about input values between 0 and 15.

    // Gates
    BIT and_gate(BIT A, BIT B);
    BIT xor_gate(BIT A, BIT B);

    // Sequential Circuits
    BIT d_latch(BIT D, BIT WE);

    // Combinational Circuits
    int adder(int O1, int O2,  BIT carryIn, BIT *carryOut);
    BIT multiplexer(BIT A, BIT B, BIT C, BIT D, BIT S1, BIT S0);
    void decoder(BIT A, BIT B, BIT *O0, BIT *O1, BIT *O2, BIT *O3);

To compile all files into a program called PA5, type the following command:

    $ make

To run the compiled program, type the following command:

    $ ./PA5

Part of this assignment is to make sure that each test is exhaustive for the gate or circuit being tested, i.e. all combinations of inputs should be tested, except for the multiplexer and the adder circuits, where you only need to test the cases shown. NOTE: you will need to determine what the correct output should be in each case and encode that in your unit test case.

MULTIPLEXER

A	B	C	D	S1	S0	Output
0	0	0	0	0	0
1	1	1	1	1	1
1	0	1	0	1	0
0	1	0	1	0	1

ADDER

O1	O2	Carryin	Output Sum	Output Carryout
0101	0101	0
0101	0101	1
0001	0111	1
0111	0111	0
1101	1101	1

Getting Started

Copy the following five files into the PA5 working directory. It is easiest to right click on the link and do a Save Target As.. for each of the files:

main.c - (write comments in this file and unit tests)
Makefile - (do not modify)
logic.h - (write comments in this file, do not modify the interface)
logic.c - (write comments in this file and modify this file to add your code)

Open a terminal and cd to the directory created in step 1.
In the terminal, type make to build the executable. You should see the following output:


Compiling each C source file separately ...
gcc -g -std=c99 -Wall -O0 -c main.c

Compiling each C source file separately ...
gcc -g -std=c99 -Wall -O0 -c logic.c

Linking all object modules ...
gcc -g -std=c99 -Wall -O0 main.o logic.o  -o PA5

In the terminal type ./PA5 to see that the program currently runs. The output should be as follows:


===== Testing not_gate =====
===== Testing or_gate =====
===== Testing rs_latch =====

As long as none of the asserts in main.c do not cause the program to halt, the implementations are correct.

You have a functioning program. There are some example unit tests in main.c and some example implementations in logic.c. You need to write comments in all of the source files, implement the rest of the functions specified in logic.h, write unit tests for all of the functions in main.c. Copy the methodology of asserts from the existing code in main for your test cases. Keep in mind that the unit test cases need to be exhaustive for all of the functions except for the multiplexer and the adder, as described above.

Submission instructions

You will be submitting a single file PA5.tar using the Checkin tab. The tar ball should include the following files: logic.c, logic.h, and main.c. The file PA5.tar is made by the Makefile, as shown above. Check your source files to make sure you have put comments in all of the source files.

Reminders

Make sure that your tar file is named PA5.tar.
Make sure that your tar file unpacks to a directory named PA5.
Test your tar file in another directorty using $ tar xvf PA5.tar
Comments headers are required for each file and function.
Function return values, names, and parameters must exactly match, including case.

Grading Criteria

To grade the assignment, we will verify that your logic functions work correctly (50 points), and that your test cases are comprehensive (25 points). In addition points will be given for coding style and comments (10 points), and following assignment directions (15 points). The grading factors we consider for coding style include having clear and concise comments, consistent indentation, and avoidance of excessive code to solve the problem. NOTE: No preliminary testing is setup for PA5, since much of the assignment is for you to test your own code!