Module 7: Assembly Language

Question 1

machine language

Answer 1

bit patterns that are directly executable by the computer

• -may look like gibberish to humans but it is actually the binary encoded instructions that the CPU can understand
• -may also contain data in addition to instructions

Question 2

assembly language

Answer 2

symbolic representation of machine langauge

• -instructions as mnemonic ASCII strings
• -cannot run but mostly readable by humans
• -can be handwritten or produced by a compiler from a high level language like C
• -assembly files can also contain ASCII lables (e.g. BRnzp LOOP)

Question 3

assembler

Answer 3

used to translate assembly programs (.ASM) into machine code (.OBJ)

Question 4

linking

Answer 4

process of connecting several .OBJ files together into one executable program

Question 5

programming

Answer 5

process of designing/writing/testing/debugging/maintaining the “source code” of computer programs

Question 6

variables

Answer 6

places to “store” information as in algebra

Question 7

loops

Answer 7

a way to “repeat” a portion of a program over and over again

Question 8

conditional control

Answer 8

a way for our program to change the natural flow of a program based on a condition

Question 9

subroutine

Answer 9

group of instructions meant to perform a specific task e.g. square a number, print out a string, etc. in assembly; similar to a “function” in a high level language

Question 10

pointers

Answer 10

variable storing a memory address (as opposed to a regular variable that holds data)

Question 11

dereferencing

Answer 11

act of using memory address held by a pointer to read/write from the memory location held onto by that pointer

Question 12

assembly directives

Answer 12

provide an indication to the assembler of where it should place various blocks of code or data

Question 13

Loops & if-else statements

Answer 13

covers: loading constants, arithmetic, compare, branch, basic jump instructions, labeling in assembling

Question 14

subroutines

Answer 14

covers: JSR, RET, labels, assembly directives: .FALIGN

Question 15

accessing data memory

Answer 15

covers: LDR, STR, what is a pointer?, for loops

Question 16

an “assembler” program

Answer 16

operates in two phases:

1. converts labels into offsets and removes comments
2. converts assembly code into machine code
   - -uses ISA to do this and saves in a .OBJ file

Question 17

Loader

Answer 17

after assembler finishes a “loader” program loads it into computer memory

Question 18

LC4 memory

Answer 18

user region

• programs run by users e.g. MS Word
• processes run in user mode with PSR[15]=0 are not allowed to access OS locations in the memory

OS region

• processes run in OS mode with PSR[15]=1
• note: address x8200, first address of your OS

Question 19

LC4 assembly directives

Answer 19

.DATA
-next values are in DATA memory
.ADDR
-set current address to the specified value
.FILL IMM16
-set value at the current address to the specified 16-bit value

ultimately, the assembly program gets assembled to an object file that is a specification for how the machine memory should be set up