Lect 13: 80486 and Pentium

1. Lect 13: 80486 and Pentium

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

3. Internal Architecture of the 80486 • Complex Reduced-Instruction-Set Computer (CRISC) • RISC integer core

4. Real-Mode Software Model • the same as that shown for the 80386

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.

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

7. System-Control Instruction Set + a flush bus cycle + a write-back bus cycle

8. Page Directory and Page Table Entries

9. Hardware Architecture of the 80486

10. Signal Interfaces Pseudo-lock

11. On-Chip Cache of the 80486SX

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

13. Internal Architecture of the Pentium Processors

14. I1 I3 I5 I7 PF I2 I4 I6 I8 I1 I3 I5 I7 D1 I2 I4 I6 I8 PF I1 I2 I3 I4 I1 I3 I5 I7 D2 I2 I4 I6 I8 D1 I1 I2 I3 I4 I1 I3 I5 I7 D2 I1 I2 I3 I4 EX I2 I4 I6 I8 I1 I2 I3 I4 I1 I3 I5 I7 EX WB I2 I4 I6 I8 I1 I2 I3 I4 WB 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

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

16. Branch Prediction • Branch Prediction • Branch Target Buffer • The processor accesses the BTB with the address of the instruction 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_loopPF • 486 : 6 clocks Pentium : 2 clocks with branch prediction

17. EFLAGS

18. Control Registers of the Pentium Processor

19. Enhancements to the Instruction Set

20. Hardware Architecture

21. Memory Subsystem

22. Organization of the DRAM Array

23. RAS/CAS address MUX

24. Data Bus Transceiver Circuitry

25. On-Chip Cache

26. On-chip cache operating mode