Programming Embedded Systems, 2nd Edition

Examine the Landscape

It is often useful to put yourself in the processor’s shoes for a while. Imagine what it is like to be the processor. What does the processor’s world look like? Who is connected to it? How does it talk to these other devices?

If you think about it from this perspective, one thing you quickly realize is that the processor has a lot of compatriots. These are the other pieces of hardware on the board, with which the processor communicates. The processor has different methods for communicating with these other pieces of hardware. In this section, you will learn to recognize their names and addresses.

The first thing to notice is that there are two basic types of hardware to which processors connect: memories and peripherals. Memories are for the storage and retrieval of data and code. Peripherals are specialized hardware devices that either coordinate interaction with the outside world or perform a specific hardware function. For example, two of the most common peripherals in embedded systems are serial ports and timers.

Members of Intel’s 80x86 and some other processor families have two distinct address spaces through which they can communicate with these memories and peripherals. The first address space is called the memory space and is intended mainly for memory devices; the second is reserved exclusively for peripherals and is called the I/O space. However, peripherals can also be located within the memory space, at the discretion of the hardware designer. ...