CS310 Resources for the LC-3 Simulator

Patt/Patel LC-3 Simulators and User's Manuals	What's installed at the UTCS Micro Lab?	UTCS LINUX TURN-IN Instructions	CS310 LC-3 Simulator FAQ and Advice
CS310 Assembly Language Documentation Guidelines	Source Code for figures & examples	UTCS linux simulator	Submit advice to webmaster

This page consists of helpful links and information for using the LC-3 Simulator in CS 310 and is intended to provide "one-stop shopping" for the LC-3.

Textbook resources: LC-3 Simulator, User's Manual, Source Code

• All of the following are found in the Patt/Patel textbook's accompanying website. 
  
• Patt/Patel have provided two LC-3 simulators that you can use at home or in the CS Labs. We encourage you to use the Windows version of the Simulator (which is also installed in the Micro Lab) for its ease of use, which includes  a debugger and a "help menu".
  
• Windows version : the .exe to download includes an editor/assembler called LC3Edit, and a loader/simulator/debugger called LC3Simulator.  Each program has a classic GUI interface, and some built-in help information.
  
• Linux Version -  (NOTE: this version has a command line assembler, a simplified debugger, missing features, and no built-in "help information")
• Note:  UTCS students built their own simulator that runs on UTCS linux.  (most of the team here has not used this)
  
• There are two LC-3 Simulator User's Manuals and are particularly helpful to read at the first.
• All source code provided in the book is also on the P/P website.

UTCS MicroLab:

• The Micro Lab (in PAI Hall) has already installed the Windows version of the LC-3 Simulator:  you will find the LC3Edit, LC3Simulator, (and I believe that the LC-3 User's Manual for Windows is also installed???)

Turnin Guidelines:
NOTE!!! We will be using the turnin program available on the UTCS Linux systems and NOT the turnin.exe program available in the PCs in the microlab!

The turnin guideline and standards are as follows:

• All the required files for the Homeworks MUST be turned in by the due date(s).
• Besides the online submission, you will often be asked to turn in a stapled hardcopy of your source file with your name, your TA's name, discussion section time
• Your source files must follow the documentation guidelines.
• Sometimes you will also be asked to include in the hardcopy a screen capture (not a text file) showing your outputs.
• You MUST ALWAYS Turn in electronically the source file with your name, your TA's name and discussion section time as part of the comments for your code (via the LINUX TURN IN COMMAND --- we do not accept turnin.exe input)
• If your program does not work, then for partial credit, it would help if you write up a README, describing what does work...
• The actual Linux turnin command has been described below:
  The turnin command is as follows:
  > /lusr/bin/turnin --submit < ta_id > < homework_id > < your_homework_file_name >
  For example : If you need to turn in HW#7 to Honguk, then type the following according to the HW FAQ:
  #53845: > turnin --submit phchung   hw7    hw7.asm
  
  

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LC-3 Assembler/Simulator FAQs & other questions:

• I was trying to "read a character" but it looks like  my program is in an "infinite loop".  What's happening?

First, Probably, the simulator is waiting for you to enter a single character into the console window.  Sometimes, it is lost behind the simulator window.

• Beware! Don't use R7 as a register for your calculations!!! Calling a trap routine (or using JSR/JSRR) will modify R7.
  
  
•   How to get my console output into the text file?

  In LC3 simulator, load your obj file and then

• 1. File->Start Console File: specify your output filename, example, h4.q5.out
• 2. Run program (put a breakpoint on HALT if needed)
• 3. File->End Console File: check the content of the out file. Its content should be same as what you've seen in the LC3 console window during running your program.
  
  
• Some homework questions ask me to turn in a .dump file by "DUMP"ing the contents of a specific section of memory, in order to turn that in as output.  How do I do this using the LC-3 simulator?

• First, debug your program, using the powerful step over button, etc... Once it is correct, then follow these steps to create the memory dump file.
  
• You will need to re-load your program.
  
• Place (“toggle”) a break point at the specified point in the program (the turn-in instructions will specify this point)
  
• Then select “run the program”.
  
• When the program stops at the breakpoint, you can see the contents of memory.  Examine it to make sure that you have captured the required information.
  
• Select “Save Memory Contents” under the “File” menu in the LC3 simulator.  The turn-in instructions will specify the values that you should supply to the  Memory Address Range.  (Choose a filename that ends with .dump)

• Some homework questions ask me to turn in a "screen dump" (or screen capture).  How do I get a screen dump (or screen capture) of an LC3 window?

On the MS Windows system, first make that window “active” by mouse-clicking anywhere in the window, and then press “ALT-Print Screen”. The dump is copied on to the clipboard. To use this in any application, just click the “paste” item in the menu bar of the edit menu in that application. You may use MS WORD or the PAINT program for this purpose.

On Unix/Linux systems, you can use the “xv” image processing program. It has a “grab” button that will let you grab the screen.

• How does one access a floppy disk on a Linux machine?

In order to use the floppy disk, you need to mount it first. Type the following command on the prompt:
> mount /floppy
(See the man pages for more information on mount). This will mount the file system and your files from the floppy will be available under the /floppy directory.
Note: the /floppy directory is under the root directory. so you have to change your directory first. Type:
> cd /floppy (this will take you to the right directory)
> ls (to view you files).
When you finish your work, you have to unmount the floppy drive. Just type > umount /floppy

• I keep getting an error message that says "A trap was executed with an illegal vector number."

  First of all, make sure that you're using a Trap vector that's actually defined. (such as x20 ~ x25)
  If that's not the problem, then it's very likely that you're using decimals instead of hexadecimals. (e.g. TRAP 25 is WRONG. TRAP x25 is correct)

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CS310 Assembly Language Documentation Guidelines:

• LC-3 programs should be written to follow these documentation guidelines.

Source Code for figures & examples:

• All source code (both LC-3 and C) from figures in the book are on the P/P website.
• Lectures:  several handouts of LC-3 examples are provided in lecture, and generated during discussion sections (see Discussion notes).
  

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UTCS unsupported LC-3 Simulator:
This is an optional simulator for use under Linux that you may choose to use.  (Note:  UTCS students built their own simulator that runs on UTCS linux.... most of the CS310 team has not yet used this tool.)

LC3 for Linux:

1. Information on how to use this simulator (from the UTCS Linux systems)
http://www.cs.utexas.edu/users/aliguori/lc3db/   (also designed to provide OS support for Interrupts)

2. To assemble an LC-3 program:
/p/bin/lc3asm filename.asm - assembles filename.asm and creates filename.obj, in addition to a couple of other files.

3. To run the simulator/debugger:

/p/bin/lc3db  --ddd   (with graphical interface)
/p/bin/lc3db    (commandline interface)

4.  As for installing lc3db locally, I just copied the following message from http://www.cs.utexas.edu/users/aliguori/lc3db

"lc3db can be run locally on an Intel-based Linux machine. The only requirement is that GNU ddd is installed if you wish to use a GUI interface. GNU ddd is available from the GNU ddd website.
There is no support provided if you run lc3db locally. It's import to run the static version from the directory you have it installed in."

5.  The UTCS simulator buttons "step" and "next" are comparable to the Windows simulator buttons: "Step Into" and "Step Over".

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If you have encountered a problem with a homework, then contact the professor.  Otherwise, if you have run into a confusion with the LC-3 assembler or simulator/debugger, and have resolved it, then please send the question & its answer to the webmaster  ( Pak Ho (Simon) Chung )   THANKS!
Last updated: 1/18/2006