CPU and Pins

1. CPU and Pins • A CPU is a VLSI chip • All chips have some pinout as its interface • CPU pins typically grouped by function • data • bus control and arbitration • coprocessor coordination • status and snooping

2. Common Pin Groups

3. The Bus • It’s just a bunch of wires • Perhaps the second most important component in the whole system • Motherboards not just built around CPU • CPUs come with “buddies” called chipsets

4. Bus = Pile of Wires

5. The Modern Bus = Caste System

6. Pentium II Bus Layout

7. Intel Chipset

8. How Many Layers? • Typically multiple buses in one system • Problem is creating appropriate layers • Usually each layer coordinates components with similar speed • Ideally the arrangement matches usage • Then next problem is how to coordinate multiple components

9. Bus Arbitration • Sometimes CPU chip contains arbitration • Other times a separate chip handles this • Hence the idea of a chipset • Bus is a shared resource • only allow one user at a time • Key arbitration mechanism is priority list • Highest priority component always wins • Smarter buses will prevent starvation

10. Arbiter Manages Requests

11. Arbitration via Daisy Chaining

12. Arbitration via Priority Encoder