Linux Kernel Architecture

Chapter 6: Device Drivers

processor architectures. It is rarely used in workstation systems because its electrical installation

is very complicated as compared to other buses (each SCSI chain must be terminated in order to

function correctly).

❑ Parallel and Serial Interfaces— These are present in most architectures regardless of the design

of the overall system. These are extremely simple and very slow connections to the outside world

and have been with us for an eternity. They are used to address slow devices such as printers,

modems, and keyboards that place no great performance demands on the system.

Regardless of the processor architecture employed,systems usually have not just one but a combination

of buses. Current PC designs generally include two PCI buses interconnected by abridge. For compatibil-

ity reasons, they sometimes also feature an ISA bus (mostly with just one slot). Some buses such as USB

or FireWire cannot be operated as main buses but always require a further system bus via which data are

passed to the processor. Figure 6-2 shows how different buses are linked in a system.

RAM CPU

I/O Memory

bus

PCI #0

PCI #1

BridgePCI

PCI Slots

Root-Hub

Hub Webcam

Mouse Keyboard

SCSI

Controller Scanner

Hard Disk

Hard Disk CD ROM

USB

Controller

Figure 6-2: Linking different kinds of buses.

Interactionwith the Peripherals

Let us turn our attention to the methods that are available to communicate with peripherals. There are

several ways of communicating with the hardware attached to the system.

I/O Scheduling

OneoptionistousetheI/OportsfoundonIA-32andmany other architectures. In this case, the kernel

sends data to an I/O controller. The device for which the data are intended then is identified by means of