Spring 2002 CSCI 255 Lab 8

This lab is scheduled for the week of 3 April - 4 April.

Goals and Methods

This week we'll look at:

  1. Assembling LC-2 programs
  2. Performing some C logical operations on the LC-2

Start off creating and then connecting to a directory called csci/255/lab8.

Assembly language programming on the LC-2

You're going to write an assembly language program for the LC-2. The program will set the values of registers R0, R1, and R2 based on the values of registers R3 and R4. Your program should not change the values of R3 and R4; however, it is free to use R5, R6, and R7 as "scratch" registers. You must be sure your is loaded at x3000.

Here is the C-code you are supposed to implement:

    R0 = !R3 ;
    R1 = ( R3 | 0x4444) & ~0x1111 ;
    R2 = R3 || R4 ;

Keep in mind that the C ! and || operators always return either 0, for false, or 1, for true. Your code should do likewise. For example, if the value of R3 is 6 and the value of R4 is 5; your code should set R0 to 0 and R2 to 1.

Getting started

We're going to make this a little easier for you by giving you a program that performs the first of the three statements:

    R0 = !R3 ;

Use the following Linux commands to obtain a copy of this program, to assemble the program, and to then list the files contained in your lab8 directory:

If you don't see a file called lab8.obj in your directory, you need to get the attention of the instructor.

Rather use Windoze

If you prefer, you can use Windows. Start by downloading the lab files in either ZIP or Windows EXE format. However, if you use windows, you must FTP your completed program back to your ~/csci/255/lab8 directory.

Testing the program

Start the LC/2 simulator by typing the command "lc2sim &" and load the object file lab8.obj. Next run the program.

Notice that this program really doesn't have any I/O: It doesn't an read initial value for R3, and it doesn't print the final value for R0. To set R3 you have to use the thenSet Value introduced in Lab 5. To discover the value of R0, just look at the LC/2 register display at the top of the simulator's window.

Test out the program with R3 set to the following values: 5, 0, and -5. You will probably want to set a breakpoint at the HALT trap to make sure the values in R0 and R1 are not changed by the HALT trap.

Instructor check-off

Show the instructor the result of running the program with R3 equal to -5.

Finishing the program

Now you need to write the remaining two lines of code for your program. Think about the code you are going to write and use pico to modify your program. If you've forgotten how to use pico, you can review Lab 2 of CSCI 107. If you have ever used pico, you can study Lab 2 of CSCI 107. If you have ever used pico.

You will undoubtedly need to cycle through pico, lc2asm, and lc2sim as your debug your program. The cycle will progress a bit faster if you keep lc2sim running while you pico and lc2asm.

Be sure to test out your program on a few different and interesting input combinations.


Presently, your program ends with a HALT trap. Make your program into a subroutine by replacing the HALT with a RET.

Now you need something to call your newly subroutinified Lab 8 program. Copy the object file /usr/local/csci/lab8/main8.obj into your directory and load it into lc2sim. This newly loaded program will prompt you for input, call your subroutine a location x3000, and display its results. It will will repeat this process until you type a ^D, control-D or ASCII EOT.

Try running the main program to give your code a more thorough testing.

Going home

When you are done, exit the simulator and log out of the Linux workstation. Do not delete your files. Your lab instructor will examine them later.

Your lab instructor can verified that your correctly copied your program by executing the following command on woodfin.