2 docs tagged with "dwt"

There is a category of bug that a breakpoint destroys by looking at it, and a log line destroys almost as thoroughly. A race between two interrupts, an occasional priority inversion, a state machine that takes a wrong branch once in ten thousand iterations — halting the core to inspect any of these changes exactly the timing that produced them, and a printf line inserted to catch them costs enough cycles to close the window it was supposed to observe. The Debug Toolbox's perturbation table already ranks every instrument in this folder by how much it disturbs the thing it is measuring; trace is the answer at the bottom of that table, the one built specifically to be close to zero.

Every piece of real-time analysis needs one number per task: how long it takes to run. Not how long it usually takes — how long it can possibly take. That number, the worst-case execution time, is the input to response-time analysis, to utilisation budgets, and to every claim that a deadline is met. It is also the hardest number in embedded engineering to obtain honestly, because the obvious way to get it — run the code and time it — cannot produce it even in principle.