Programming Embedded Systems, 2nd Edition

Chapter 7. Peripherals

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 handful of other hardware devices. Some of these devices are specific to each embedded system’s application domain, while others—such as timers/counters and serial ports—are useful in a wide variety of systems. The most commonly used devices are often included within the same chip as the processor and are called internal, or on-chip, peripherals. Hardware devices that reside outside the processor chip are, therefore, said to be external 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

An embedded processor interacts with a peripheral device through a set of control and status registers. These registers are part of the peripheral hardware, and their locations, size, and individual meanings are features of the peripheral. For example, the registers within a serial controller are very different from those in a timer. In this section, we’ll describe how to manipulate the contents of these control and status registers directly from your C language programs.

As discussed in Chapter ...