CS 2318 (Assembly Language) by Lee S. Koh
Exam 2 Study Guide
■ General


● When:


    SectionDateStart Time


    25104-03-2025 (Thursday)11:00 am


    255 & 256
04-03-2025 (Thursday)06:30 pm

● Duration: 1 hour 20 minutes.

● Questions can be on anything up to and including the lectures on 10/31/2024 (upcoming Thursday).


► That means the most relevant lecture notes are
 005a NotesOnBitwiseOperations
 006 ComputerOrg&DesignOverview01
 007 ComputerOrg&DesignOverview02
 008 MIPS32ArchitectureOverview
 009 MIPS32AssemblyLanguageGettingStarted
 010 MIPS32AssemblyLanguageDoingBasics01
 010a MIPS32AssemblyLanguageDoingBasics01_SomeDetailsQuirks
 011 MIPS32AssemblyLanguageDoingBasics02
  011_MIPS32AssemblyLanguageDoingBasics02_KeySlidesEtc

● Test will be closed books / notes / online-resources / discussion and no calculating devices of any kind are allowed.


► All allowed reference material (such as the first 2 pages of this posted under Other Resources) will be provided as part of the exam.

■ Checklist of (most if not all) the things you are expected to know and/or know how to do/apply:
(NOTE: Some items seen earlier have been bolstered/deepened, so they can re-appear here.)


● Know about bitwise operations, what they are useful for, and how to put them to use.


► What bit shifting is and how it can be useful.



○ Logical left shift, logical right shift, arithmetic right shift.



○ Efficient multiplication and division by powers of 2 for signed/unsigned numbers (and unsigned floating-point numbers) represented in binary.




♯ How, and under what provisions (for results to be valid).



○ Simply to bring certain bit(s) to certain desired position(s).


► What binary bitwise operation(s) and mask(s) to use to attain certain effects (setting/clearing/toggling/complementing/extracting/isolating/... of bit(s)).



○

Bitwise-AND

 -->

1 shows, 0 hides (behind 0)




(bit clearing with 0)

Bitwise-OR

 -->

0 shows, 1 hides (behind 1)




(bit setting with 1)

Bitwise-XOR

 -->

0 shows, 1 hides (behind "the reverse of actual")

(bit toggling with 1)



○ What combination of operation and mask to use to go from what's given to what's desired.


► XOR intrigue:



○ Same polarity gives 0, different polarity gives 1.



○ XOR a bit pattern P with itself makes P all 0's (clears P).

● The 4 main components of a computer system (based on the von-Neumann architecture).


► CPU (processor), main memory, I/O devices, main (system) bus.

● The 3 buses that form the system bus.


► Address, data, control.

● What register and register file refer to (in reference to the main processor).

● Know about the program counter (PC) and instruction register (IR) - what they are for.

● Know about the memory hierarchy of the typical computer: register -> cache memory -> main memory (RAM) -> disk ...

● What datapath and control are (from functional standpoint).


► "brawn" and "brain".

● What an instruction is (especially what its 2 main parts are: opcode and operands) and what an instruction set is.

● What 3 possible places the actual value of an operand (required to execute an instruction) may be located (for our programming purpose).


► In register, in memory, embedded within instruction - the last of the three is referred to as immediate in MIPS.

● What addressing mode means.


► Way of specifying the location(s) of operand(s) involved in an instruction - each operand may be a soure operand or a destination operand.

● The main differences between CISC and RISC.


► RISC design principles (C2S2).



○Smaller is faster.



○Simplicity favors regularity.



○Make the common case fast.



○Good design demands making good compromises.


► How certain MIPS design characteristics relate to RISC design principles.



○E.g.: Which design principle best explains why MIPS $0 register is hardwired to always contain 0.

● Big picture understanding of what pipelining is.


► Goal is to enhance throughput (how much is done per unit time).

● Know about programmer's view of main memory: linear pool of storage locations, memory addresses, address space.

● What byte addressable memory mean.


► There's an address for each byte (at each byte boundary), not for each bit and not just for each (multi-byte) word.

● Know what load and store memory operations are.

● Know that memory operations are relatively slow (relative to accessing registers).

● What it means when an architecture is described as a load-store architecture.


► Only load and store instructions access (read from or write to) main memory.

● MIPS32 architectural overview.


► CPU, memory, Coprocessor 0, Coprocessor 1.


► Some 32's about MIPS32.



○ 32 general purpose registers.



○ Each general purpose register is 32 bits wide.



○ 32-bit address --> 4GB address space.



○ 32-bit word.



○ Uses 32-bit (a word) to represent integer data type .



○ Each (and every) instruction is 32-bit wide --> fixed width.


► The typical (conventional) layout of the virtual memory address space.



○ Text, data (static and dynamic) and stack segments and reserved memory.




♯ Text segment --> where.program code will be placed.




♯ Static data segment --> where.global data will be placed.




♯ Stack segment --> where (non-static) local data will be placed.


► Preliminaries on MIPS32's general purpose registers.



○ Names used to reference them.



○ Need for usage convention --> to regulate use of shared resource (many competing parties, 1 register file).




♯ Preliminary notions: $0, $v#, $a#, $t# ( temporary ), $s# ( saved ), others.





(Due to MIPS register usage convention, do not use the $s# ( saved ) registers until explicitly required to use them later, if ever.)

● MARS and first-program basics.


► MARS interface basics.



○ Key panes/windows, tab-metaphor, ...


► What the 3 categories of MIPS assembly language statements are and things about them.



○ Assembler directives --> each begins with a dot --> for use by assembler --> DON'T produce machine instructions.



○ (True) Instructions --> supported by assembler and by hardware --> each has an opcode assigned.



○ Pseudoinstructions --> supported by assembler but not by hardware --> opcode not applicable.




♯ Assembler translates each pseudoinstruction into 1 or more (true) instructions.
NOTE: Thus, each pseudoinstruction (unlike assembly directive) effectively/ultimately DOES produce machine instruction(s).


► Labels.



○ Enables programmer to mark strategic data/code locations --> for referencing convenience during coding.




♯ C/C++ variable and function names both map to labels in assembly language.



○ Key helper item generated/used by assembler to support labeling --> symbol table.




♯ Primarily, a tabular list of what address each symbol corresponds to.


► System services.



○ How a typical syscall is made --> basic I/O and graceful exit.




♯ Know how to write code involving syscall to do integer I/O.




♯ Know how to write code involving syscall to do (null-terminated) string I/O.




♯ Know how to write code involving syscall to do character I/O.

● How to use MIPS assembler directives.


► Segment declaration: .data and .text in particular.


► Data segment (global) storage space reservation/initialization/naming: .asciiz, .word, .byte and .space in particular.


► Miscellaneous specification: .globl in particular.

● How to write assembly language code to perform relatively simple tasks:


► Writing program segments involving arithmetic, bit manipulation and main memory data movement.



○ Addition/subtraction/multiplication/division involving integers.




♯ Bit-shifting for multiplications/divisions by powers of 2.



○ and and andi, or and ori, xor and xori, sll, srl and sra.
(MIPS also supports nor but either disregarded or only mentioned in passing here.)




♯ Bit manipulations (including masking) for various desired effects.



○ lb and lw, sb and sw.




♯ Pointer-arithmetic and memory-alignment traps.


► Know how to re-write C++ code involving selection (if and if-else) and/or repetition (for, while and do-while) and/or one-way transfer (break and continue) in terms of conditional and unconditional goto's.



○ (NOTE: Prerequisite C++ neatly used to play "pseudo-code" role in this course.)



○ May be nested and may involve compound conditions (i.e., conditions involving logical AND and/or logical OR).



○ Questions testing student's ability to read (interpret)/debug/complete/modify/... code involving above use of conditional and unconditional goto's are common/popular.

■ Other


● Other relevant material.


► Use Assignment 2 (up to and including Assign02P2) as part of the preparation.


► In-class examples (posted under Examples).

● You may want to check out sample past Exam 2 questions already posted on the class homepage.


► You should not however, expect the questions to be identical in number, kind, topic coverage, etc.

● You should not have to worry about questions being written on topics we have not yet covered.


► NOTE that to fully answer some questions may require knowledge and application of material covered previously.

● Do the following if you are eligible and intend to use ATSD-supported accommodations (extended time, . . .):


► Follow proper procedure to request taking the exam at the ATSD.



○You typically need to do the request at least a certain number of (non-weekend?) hours in advance.



○The start time of your request should be the closest to your class start time on exam date.