Programming Embedded Systems in C and C++

84

Chapter 7

In this chapter:

• Control and Status

Registers

• The Device Driver

Philosophy

• A Simple Timer

Driver

• Das Blinkenlights,

Revisited

7

Peripherals 7.

Each pizza glides into a slot like a circuit board into a

computer, clicks into place as the smart box interfaces

with the onboard system of the car. The address of the

customer is communicated to the car, which computes

and projects the optimal route on a heads-up display.

—Neal Stephenson

Snow Crash

In addition to the processor and memory, most embedded systems contain a hand-

ful of other hardware devices. Some of these devices are specific to the applica-

tion domain, while others—like timers and serial ports—are useful in a wide variety

of systems. The most generically useful of these are often included within the

same chip as the processor and are called internal, or on-chip, peripherals. Hard-

ware devices that reside outside the processor chip are, therefore, said to be exter-

nal peripherals. In this chapter we’ll discuss the most common software issues that

arise when interfacing to a peripheral of either type.

Control and Status Registers

The basic interface between an embedded processor and a peripheral device is a

set of control and status registers. These registers are part of the peripheral hard-

ware, and their locations, size, and individual meanings are features of the periph-

eral. For example, the registers within a serial controller ...