Diagnosing Rare Missed Timing Windows: Late Start Versus Long Run Time

A device that runs smoothly for months may suddenly miss its communication window once in thousands of cycles, with no clear error in the logs. Logs record discrete events rather than task durations, so they cannot easily reveal whether the work started late or simply ran long. Such rare faults tend to surface only after long uptimes, when independent activities happen to align, such as an interrupt burst coinciding with a held lock. The proposed technique records worst-case start lag and run time separately, along with a debug GPIO pulse and a small ring-buffer trace, to show whether delays happen before or during task execution. Interpreting the results is straightforward: a large run time points to a slow task or mid-run preemption, while a large start lag with a normal pulse points to preemption or blocking before the task begins.