Midterm #1 Review February 1, 2013 1 / 11 I will provide . . . - - PowerPoint PPT Presentation

Midterm #1 Review

February 1, 2013

1 / 11

I will provide . . .

• ASCII character encoding table
• powers of 2 up to 215
• a list of relevant instructions for assembly problems
• just the names!
• you should know the difference between: add and addi;

move, lw, sw, and la

• the interfaces of relevant system calls

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You should bring . . .

• a pencil and eraser
• one page of notes (optional)

No calculator!

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Structure of test

Part 1: Computer architecture vocabulary

• FDX cycle, datapath, control unit, bus
• multiplexor, control signal, conditional signal, clock
• program counter, instruction register, register file, ALU
• memory, text segment, data segment

Part 2: Representing integers and base conversion

• decimal ⇔ binary
• binary ⇔ hexadecimal
• two’s complement representation

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Structure of test

Part 3: Representing strings

• ASCII character encoding
• null-terminated strings and null-padding
• big-endian vs. little endian

Part 4: Integer arithmetic

• adding and multiplying signed integers

(helpful to understand carryout vs. overflow)

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Structure of test

Part 5: MIPS assembly

• encode math expressions as sequence of instructions
• declare variables and constants in data memory
• how to read and write memory (lw and sw)
• how to use system calls

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Representing integers and base conversion

Assume all integers are signed and in big-endian form

• Use two’s complement notation for negative numbers

Exercises

• 1. Convert decimal 102 into an 8-bit integer in binary
• 2. Convert decimal -102 into an 8-bit integer in binary
• 3. Convert decimal -844 into a 16-bit integer in binary
• 4. Write decimal -844 as a 16-bit integer in hexadecimal
• 5. Convert signed 16-bit integer 0xFACE into decimal

Powers of 2 n 1 2 3 4 5 6 7 8 9 10 . . . 2n 1 2 4 8 16 32 64 128 256 512 1024 . . .

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Representing strings

ASCII character encodings Assume 32-bit words and addressable bytes (as in MIPS) Encode “Aye, aye!” as a null-terminated ASCII string

• using big-endian byte ordering
• using little-endian byte ordering

(Give each byte in hexadecimal)

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Binary arithmetic

Assume all numbers are signed, 8-bit integers For each arithmetic expression:

• 1. convert the arguments to binary
• 2. perform the operation on the binary representation
• 3. convert back to hexadecimal
• 0x53 + 0x1B
• 0xB3 + 0xE9
• 0x0B × 0x06

← multiply!

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Assembly programming

# Pseudocode: # c = (a+3) * (b-2) + a # Register mappings: # a: $t0 # b: $t1 # c: $t2

Instructions you may need:

• li, add, addi, sub, subi, mul
• note: mul is a macro instruction that takes three registers:

mul $t0,$t1,$t2 # hi,lo = $t1 * $t2; $t0 = lo

• you can assume result is 32-bits (hi = 0)

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Assembly programming (solution)

# Pseudocode: # c = (a+3) * (b-2) + a # Register mappings: # a: $t0, b: $t1, c: $t2 # tmp1: $t3, tmp2: $t4, tmp3: $t5

+ + * a 3 a

• b

2 tmp1 tmp2 tmp3

addi $t3, $t0, 3 # tmp1 = a+3 subi $t4, $t1, 2 # tmp2 = b-2 mul $t5, $t3, $t4 # tmp3 = tmp1 * tmp2 add $t2, $t5, $t0 # c = tmp3 + a

Register optimization (optional)

addi $t3, $t0, 3 # tmp1 = a+3 subi $t2, $t1, 2 # c = b-2 mul $t2, $t3, $t2 # c = tmp1 * c add $t2, $t2, $t0 # c = c + a

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