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CMPT 250 Computer Architecture. Instructor: Yuzhuang Hu [email protected] Design strategy in ASM. CISC Architecture.

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Presentation Transcript
cisc architecture
CISC Architecture
  • The goal of the CISC architecture is to match more closely the operations used in programming language and to provide instructions that facilitate compact programs and conserve memory.
  • A purely CISC architecture has the following properties:
    • Memory access is directly available to most types of instructions.
    • Addressing modes are substantial in number.
    • Instruction formats are of different lengths.
    • Instructions perform both elementary and complex operations.
combined cisc risc organization
Combined CISC-RISC Organization

Instruction fetch

Microprogram counter

Decode and operand fetch

Control ROM

Execute

Write-back

cisc cpu instruction formats
CISC CPU Instruction Formats

31

25

24

20

19

15

14

10

9

0

Three register type

OPCODE

DR

SA

SB

Two register type

OPCODE

DR

SA

Immediate

Branch 1

OPCODE

DR

SA

Large target offset

Branch 2

OPCODE

DR

SA

SB

Short target offset

micro programmed control
Micro-programmed Control

SA

CA

CA-1

MS

MI

+1

MZ

0 1 2 3

Mux E

ME

MZ-1

MC

PS

Z

Address

Microcode ROM

Data

MZ

CA

DOF

EX

MZ-1

CA-1

a personal computer
A Personal Computer

Screen

Hard drive

Keyboard

Drive Controller

Bus Interface

Graphics Adapter

RAM

Processor

CPU, FPU, MMU

Internal Cache

External Cache

access times
Access Times
  • Cache: 1 ns, memory: 10 ns, hard drive: 13 ms
  • Assume that 95% of the fetches will be from a cache and about 4.999995 percent of the fetches will be from main memory. The average access time then is:
    • 0.95*2+0.49999995*10+5*10-8*1.3*107=3.05ns
locality of reference
Locality of Reference
  • Temporal Locality: refers to the relative times at which instructions and operands are accessed.
  • Spatial Locality: refers to the relative locations at which they reside in main memory.
write methods
Write Methods
  • Write the result into main memory. This is also called write-through.
  • Write the result into the cache if there is a cache hit. This is also called write-back.
    • write-allocate: when a cache miss happens, read the line containing the word to be written from main memory into the cache, with the new word written into both the cache and main memory. Dirty bit of a line.
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