Rule #13: All variables shall be initialized before use.

Reasoning: Too many C programmers assume the C run-time will watch out for them. This is a very bad assumption, which can prove dangerous in a real-time system. We may sometimes get lucky with C startup code that zeros all uninitialized data or the stack. But lucky is not acceptable in a medical device or any other safety-critical product. By making initialization before use a hard rule on your project, you elevate the warning a static-analysis tool can raise on this to an error that must be dealt with by the team.

Rule #14: The names of all global variables shall begin with the letter 'g'. For example, g_zero_offset.

Reasoning: Eschew them all you like, but global variables are a fact of life in some parts of embedded software. There are two specific risks associated with their use.

The first risk of global varilables is that a race condition between two or more asynchronous entities (be they CPUs, peripherals, ISRs, tasks, or a combination) will corrupt the data stored there. To prevent this, exclusive access must be established programmatically, such as via use of interrupt disables or mutex acquisition. The second risk is that the compiler will optimize away one entity's read or write because it cannot see the other user during compilation. Both risks can be eliminated, but only if everyone on the team sees that they are global variables. By naming all globals in an obvious way, code reviews become that much more effective--all the way down to the individual line of code or function.