Introduction

The program handin33 will only submit files in the cs33/labs/04 directory. (You can run update33 first to set up the directory first.)

You are encouraged to work with a partner; however, you may work alone if you choose to do so.

In this lab, you will write machine language and assembly language programs for the LC-3, convert them to object code for the LC-3 (lc3convert for machine language programs, lc3as for assembly language programs), and then run them in the LC-3 simulator (lc3sim-tk).

Your programs must follow these following guidelines:

• Each file should be named using provided name, and you must follow any instructions concerning memory addresses to use. Otherwise, evaluating your work is exceedingly difficult.
• Each machine language program should compile without errors using the lc3convert program and be written in binary.
• Each assembly language program should compile without errors using the lc3as program.
• Each binary instruction should be commented with a description of the actual operation you are performing. For example:

       0101 010 011 0 00 101    ; AND R2, R3, R5 (or R2 = R3 AND R5)
       0000 011 000000011       ; BRzp #3
  

  WARNING: One of the hardest errors to figure out occurs when you change the comment without changing the code. For example, in the BRzp line above, changing BRzp to BRp in the comment does not change your program... you need to also change the binary code. Always verify your program with what the simulator believes you have typed in to be sure you don't get caught by this nasty problem.
• In both machine language and assembly language, sequences of code which perform a single logical operation should be commented above the block, and a newline should separate it from the next block:

       (machine language example)
       ; Store in R3 the value of -R2 (negative R2)
       1001 011 010 111111 ; NOT R3, R2 (or R3 = NOT R2)
       0001 011 0111 00001 ; R3 = R3 + #1
  
       (assembly language example)
       ;; Shift R3 to the left two places
       ADD     R3, R3, R3
       ADD     R3, R3, R3
  

• If a portion of your program is data, you should indicate that:

       ...
       ...
       1111 0000 0010 0101      ; TRAP x25 (or HALT)
  
       ; Data
       0000 0000 1111 1111      ; Bit mask for low order bits
       1111 0111 0011 0001      ; The value xF731
  

For this lab assignment, all programs should begin at x3000 and, unless otherwise specified, should not make any assumptions about the initial state of registers or memory locations.

Machine Language

Write a program called countOnes.bin which counts the number of bits that are set to 1 in memory location x2FFE and stores the result in memory location x2FFF. You will have to manually set the value in memory location x2FFE before your program begins.

Your solution should use a loop to count the bits -- don't just list the same sequence of instructions 16 times to accomplish this task.

Challenge: Can you complete this program in 8 instructions or less -- including the HALT instruction?

Assembly Language

Write a program called dec2bin.asm which converts numbers typed in ASCII into their binary equivalent. Your program should read a decimal value (made up of multiple digits) from the keyboard and then output the binary value to the screen. Keyboard input is terminated when the user presses enter.

For example, here the user enters the decimal value "4304" which yields the binary result "0001000011010000".

Input a character> 4

Input a character> 3

Input a character> 0

Input a character> 4

Input a character> 

0001000011010000

To avoid complicating issues, you should assume that the user always enters input from keyboard that consists only of the digits 0 through 9 and Enter -- there's no need to do any error checking. Also, you should assume -- again, don't error check -- that all values are positive, and that the user will not type a value larger than (2¹⁵ - 1) = 32767.

Though this might sound quite complicated, if you break the problem into two halves, it's quite manageable:

1. In the first half, you need to read digits from the keyboard and store these digits as a single number in a register. You don't have to actually convert it to binary -- simply by storing the numerical value in the register, you're storing it in binary!
2. In the second half, you need to print the contents of that register to the screen.

This program is obviously more complicated than the countOnes program, but my fairly straightforward implementation (not doing anything fancy) took 40 instructions including some data. That's not to say your solution won't take more or less: it's just a ballpark number to give you some idea of the complexity of the problem.

Extra challenging (optional): In a file called dec2hex.asm, change your previous program so that it converts decimal input into hexadecimal output. (It's not trivial, but it's not as hard as it seems at first... my implementation took 57 instructions including some data.)