Programming Embedded Systems, 2nd Edition

Life As an Embedded Software Developer

Let’s now take a brief look at some of the qualities of embedded software that set embedded developers apart from other types of software developers. An embedded software developer is the one who gets her hands dirty by getting down close to the hardware.

Embedded software development, in most cases, requires close interaction with the physical world—the hardware platform. We say “in most cases” because there are very large embedded systems that require individuals to work solely on the application-layer software for the system. These application developers typically do not have any interaction with the hardware. When designed properly, the hardware device drivers are abstracted away from the actual hardware so that a developer writing software at the application level doesn’t know how a string gets output to the display, just that it happens when a particular routine is called with the proper parameters.

Hardware knowledge

The embedded software developer must become intimately familiar with the integrated circuits, the boards and buses, and the attached devices used in order to write solid embedded software (also called firmware). Embedded developers shouldn’t be afraid to dive into the schematics, grab an oscilloscope probe, and start poking around the circuit to find out what is going on.

Efficient code

Because embedded systems are typically designed with the least powerful and most cost-effective processor that meets the performance requirements of the system, embedded software developers must make every line of code count. The ability to write efficient code is a great quality to possess as a firmware developer.

Peripheral interfaces

At the lowest level, firmware is very specialized, because each component or circuit has its own activity to perform and, furthermore, its own way of performing that activity. Embedded developers need to know how to communicate with the different devices or peripherals in order to have full control of the devices in the system. Reacting to stimuli from external peripherals is a large part of embedded software development.

For example, in one microwave oven, the firmware might get the data from a temperature sensor by reading an 8-bit register in an external analog-to-digital converter; in another system, the data might be extracted by controlling a serial bus that interfaces to the external sensor circuit via a single wire.

Robust code

There are expectations that embedded systems will run for years in most cases. This is not a typical requirement for software applications written for a PC or Mac. Now, there are exceptions. However, if you had to keep unplugging your microwave in order to get it to heat up your lunch for the proper amount of time, it would probably be the last time you purchased a product from that company.

Minimal resources

Along the same lines of creating a more robust system, another large differentiator between embedded software and other types of software is resource constraints. The rules for writing firmware are different from the rules for writing software for a PC. Take memory allocation, for instance. An application for a modern PC can take for granted that it will have access to practically limitless resources. But in an embedded system, you will run out of memory if you do not plan ahead and design the software properly.

An embedded software developer must closely manage resources, from memory to processing power, so that the system operates up to specification and so failures don’t occur. For example, using standard dynamic memory allocation functions can cause fragmentation, and eventually the system may cease to operate. This requires a reboot since you have no place to store incoming data.

Quite often, in embedded software, a developer will allocate all memory needed by the system at initialization time. This is safer than using dynamic memory allocation, though it cannot always be done.

Reusable software

As we mentioned before , code portability or code reuse—writing software so that it can be moved from hardware platform to hardware platform—is very useful to aid transition to new projects. This cannot always be done; we have seen how individual each embedded system is. Throughout this book, we will look at basic methods to ensure that your embedded code can be moved more easily from project to project. So if your next project uses an LCD for which you’ve previously developed a driver, you can drop in the old code and save some precious time in the schedule.

Development tools

The tools you will use throughout your career as an embedded developer will vary from company to company and often from project to project. This means you will need to learn new tools as you continue in your career. Typically, these tools are not as powerful or as easy to use as those used in PC software development.

The debugging tools you might come across could vary from a simple LED to a full-blown in-circuit emulator (ICE). This requires you, as the firmware developer, and the one responsible for debugging your code, to be very resourceful and have a bag of techniques you can call upon when the debug environment is lacking. Throughout the book, we will present different “low-level software tools” you can implement with little impact on the hardware design.

These are just a few qualities that separate embedded software developers from the rest of the pack. We will investigate these and other techniques that are specific to embedded software development as we continue.