Lect 13-1

Lect 13: 80486 and Pentium

Lect 13-2

80486 Microprocessor Family

80486 Microprocessor Introduced in 1989 High Integration

On-chip 8K Code and Data cache Floating Point Unit Paged, Virtual Memory Management

168-pin PGA package Multiprocessor Support

Multiprocessor Instructions Cache Consistency Protocols

Lect 13-3

Internal Architecture of the 80486

Complex Reduced-Instruction-Set Computer (CRISC) RISC integer core

Lect 13-4

Real-Mode Software Model

the same as that shown for the 80386

Lect 13-5

Protected-Mode Software Architecture

AC: Alignment-Check flag When this bit is set, an alignment check is performed during all memory accesses at privilege level 3. If an unaligned access takes place, exception 17 occurs.

Lect 13-6

Control Registers

AM : alignment mask -- If this is switched to 0, the alignment check is masked out.

NE : Numeric Error CD : cache disable NW : not write-through WP : write protect

• PCD : page-level cache disable• PWT : page-level write transparent

Lect 13-7

System-Control Instruction Set

+ a flush bus cycle

+ a write-back bus cycle

Lect 13-8

Page Directory and Page Table Entries

Lect 13-9

Hardware Architecture of the 80486

Lect 13-10

Signal Interfaces

Pseudo-lock

Lect 13-11

On-Chip Cache of the 80486SX

Lect 13-12

Pentium Processor

Pentium Processor 32-bit Microprocessor

32-bit addressing 64-bit Data Bus

Superscalar architecture Two pipelined integer units Capable of under one clock per instruction Pipelined Floating Point Unit

Separate Code and Data Caches 8K Code, 8K Write Back Data 2-way 32-byte line size MESI cache consistency protocol

Advance Design Features Branch Prediction

237-pin PGA

Lect 13-13

Internal Architecture of the Pentium Processors

Lect 13-14

Pentium Processor

Pipeline and Instruction Flow 5 stage pipeline

PF : prefetch

D1 : Instruction decode

D2 : Address Generation

EX : Execute -ALU and Cache Access

WB : Write Back

Intel 486 Pentium

I1 I3I2 I4

I1 I3I2 I4

I1 I3I2 I4

I1 I3I2 I4

I1 I3I2 I4

PF

D1

D2

EX

WB

I1

I2

I5

I6

I7

I8

I3

I4

I1

I2

I5

I6

I7

I8

I3

I4

I1

I2

I5

I6

I7

I8

I3

I4

I1

I2

I5

I6

I7

I8

I3

I4

I1

I2

I5

I6

I7

I8

I3

I4

PF

D1

D2

EX

WB

Lect 13-15

Pentium Processor

“U”, “V” pipes - “pairing” U : any instruction V : ‘simple instructions” as defined in the ‘Pairing” rules

PF : instructions on chip cache or memory -> prefetch buffers

prefetch buffers - two independent pairs of line size(32 bytes)

D1 : two parallel decoders

D2 : address generation for operand fetch

EX : ALU operations and data cache access

WB : modify processor state ; complete execution

Lect 13-16

Branch Prediction

Branch Prediction Branch Target Buffer The processor accesses the BTB with the address of the instructi

on in the D1 stage

example)

inner_loop : mov byte ptr flag[edx], al PF D1 D2 EX WB

add edx, ecx PF D1 D2 EX WB

cmp edx, FALSE PF D1 D2 EX WB

jle inner_loop PF

486 : 6 clocks

Pentium : 2 clocks with branch prediction

Lect 13-17

EFLAGS

Lect 13-18

Control Registers of the Pentium Processor

Lect 13-19

Enhancements to the Instruction Set

Lect 13-20

Hardware Architecture

Lect 13-21

Memory Subsystem

Lect 13-22

Organization of the DRAM Array

Lect 13-23

RAS/CAS address MUX

Lect 13-24

Data Bus Transceiver Circuitry

Lect 13-25

On-Chip Cache

Lect 13-26

On-chip cache operating mode