CSCI 211 Intro

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CSCI 211 Intro

• Computer Organization
• Consists of gates for logic
• And
• Or
• Not
• Processor
• Memory
• I/O interface

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Instructions

• Instructions are in memory
• Fetch instruction, then execute it
• Fetch execute cycle
• More detailed
• Fetch instruction
• Fetch operands
• Execute instruction
• Save result
• Determine next instruction

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Processor Components

• Datapath
• Hardware that electrons flow through to
  accomplish an instruction
• Control
• Tells hardware what to do and when to do it.
• Registers
• Small amount of memory (32 4-byte for MIPS) that
  can be operated upon.

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Whats inside

• Everything in the computer is represented with
  0s and 1s (on-off)
• Integers
• Characters
• Boolean
• Float
• Instructions (machine language)

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Languages

• Machine Language
• Just 0s and 1s
• Very hard to program
• Assembly
• Symbolic for machine language
• Easy to create a program to translate from
  assembly language to machine language (almost 1
  to 1)
• Keeps track of variables addresses

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Why Learn Assembler

• Understand what the machine does
• Helps you to be a better guesser
• Needed to write a compiler (431)
• Needed to build CPUs
• Faster to execute
• To determine timing
• Gives you the power to access anything
• Maintaining older systems

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Why not USE assembly

• Tedious
• Error prone
• Slow to write
• Machine dependent
• Good compilers produce fast code already

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MIPS CPU

• Used in many systems
• SGI workstations
• Sony PS2
• Dish Network set top box
• Tivo DVR
• Pioneer Plasma TV
• HP Color laser printer
• Many more

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MIPS Layout

• Control
• Register file (32 registers with 32 bits each)
• ALU
• Program Counter (PC)
• Memory
• 32 bit address (232 bytes addressable 4Gb)
• Instruction register (IR)

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Control Unit

• Sends the proper control signals to each
  component to accomplish instruction
• Input to the control unit
• Instruction
• Cycle number which step of the instruction

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Register File

• A group of registers
• Input
• Which register (5 bits)
• Read or Write
• 32 bit value (for write)
• Outputs a 32 bit value for read

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Register Conventions

• 0 0
• 1 used by the assembler
• 2, 3 function return values
• 4-7 Arguments to a function
• Etc.

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Other components

• ALU
• Performs arithmetic and logic (and, or, shift)
• PC
• Program counter address of next instruction
• Memory
• 32 bit address
• Addresses a byte (8 bits)
• Some instructions use word (4 bytes), halfword (2
  bytes), or byte operands
• All instructions are 4 bytes (on MIPS)
• PCPC4

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Instruction Register

• IR
• Holds the 32 bit instruction just fetched
• Needed for control unit to determine what control
  signals to send

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Instruction Format

• Opcode
• First 6 bits
• 3 Formats
• R type
• Opcode all 0s
• Three 5-bit fields for registers (2 for operand,
  1 for result)
• 5-bit shift amount (for shift instructions)
• 6-bit function code

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Other formats

• I Type
• Two 5-bit register numbers
• 16-bit value as the third operand
• J type
• Jump instructions
• 26 bit address field (64M)