Despite all the different embedded designs I worked on, one of the projects that stands out the most is the first embedded project I worked on – despite the fact that I already had ten years of experience with programming computers before that. I had received money for writing simulators, database engines, an assembler, a time share system, as well as several automation tools for production systems. All of these projects executed on mainframe systems or desktop computers. None of them quite prepared me for how different working on an embedded design is.
My first embedded design was a simple box that would reside on a ground equipment test rack that supported the flight system we were building and demonstrating. There was nothing particularly special about this box – it had a number of input and select lines and it had a few output lines. What surprised me most when putting it through its first checkout tests was how clueless I was as to how to troubleshoot the problems that did arise.
While I was aware of keyboard debounce routines from using my desktop system, I had never had to so completely understand the characteristics of different types of switches before. I had never before had to be aware of the wiring within the system, nor had I ever even considered doing an end-to-end check on every wire in a system ever before. While putting this simple box together, I became aware of so many new ways a design could go wrong that I had never had to consider in my earlier designs.
On top of the new ways that the system could behave incorrectly, the system had no file system, no display system, and no way to print out a trace log or memory dump. This made debugging a very different experience. Printf statements would be of no use, and there was no single-step debugger available. Worse yet, running the target program on my desktop computer, so that it could simulate the code, was mostly useless because I could not bring the real-world inputs and outputs that the box worked with into the desktop system.
As I tackled each debugging issue, I went from a befuddled state of having no idea how to proceed to a state where I adopted new ways of thinking that let me gain the insights I needed to infer how the system was (or was not) working and what needed to change. I worked on that project alone, and it welcomed me into the world of embedded design and working with real world signals with wide open arms.
How did your introduction to embedded systems go? What insights can you share to warn those that are entering the embedded design community about how designing, debugging, and integrating embedded components is different from writing application-level software?
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