I am often asked questions about embedded software. Sometimes they are complex; other times they are simple. But frequently, the simplest ones are what leads to an interesting train of thought. The one that set my brain working recently was something like this: “I have some non-volatile memory in my design, which is used to retain specific parameters through power cycling. The first time the device is used, the memory contains garbage and needs to be initialized. When the software starts up, how can I detect that this is the first time it has executed and an initialization sequence needs to be run?”

My first thought was to suggest that simple inspection of the data would show whether it was valid or not. In some applications, that would certainly be true. In others, perfectly valid data could look like a jumble of ones and zeros. There must a be simple, reliable way to make it clear that the memory/data has been initialized … (more…)