Programming Embedded Systems, 2nd Edition

Chapter 6. Memory

Tyrell: If we give them a past, we create a cushion for their emotions and, consequently, we can control them better.Deckard: Memories. You’re talking about memories.

—the movie Blade Runner

In this chapter, you will learn everything you need to know about memory in embedded systems. In particular, you will learn about the types of memory you are likely to encounter, how to test memory devices to see whether they are working properly, and how to use flash memory.

Types of Memory

Many types of memory devices are available for use in modern computer systems. As an embedded software engineer, you must be aware of the differences between them and understand how to use each type effectively. In our discussion, we will approach these devices from a software viewpoint. As you are reading, try to keep in mind that the development of these devices took several decades. The names of the memory types frequently reflect the historical nature of the development process.

Most software developers think of memory as being either RAM or ROM. But, in fact, there are subtypes of each class, and even a third class of hybrid memories that exhibit some of the characteristics of both RAM and ROM. In a RAM device, the data stored at each memory location can be read or written, as desired. In a ROM device, the data stored at each memory location can be read at will, but never written. The hybrid devices offer ROM-like permanence, but under some conditions it is possible to overwrite ...