Troubleshooting real-time software issues using a logic analyzer

This logic analyzer technique is a power-tool for the embedded software engineer’s toolbox.

While many embedded software issues can be debugged using either print statements or symbolic debuggers (such as JTAG tools), there are many instances where neither of those methods can help. For example, suppose the problem is in an interrupt handler that is executing ten thousand times per second. It’s not practical to put print statements as that will ruin the real-time execution. Adding breakpoints to monitor the interrupt will likely break functionality.

Another example is synchronization and timing errors in real-time systems. Developers regularly add mutexes, semaphores, condition variables, or other mechanisms to guard shared resources. But how do you test and debug an issue with these mechanisms? Can you tell whether or not a race condition or priority inversion is actually occurring? How do you track down a glitch that only happens randomly? Can you identify the root cause of a particular real-time constraint not being met?

To troubleshoot these types of real-time issues, the logic analyzer, which traditionally is used by hardware engineers to debug their digital circuits, can be the software engineer’s best aide. It provides a new power-tool for your software debugging toolbox. It enables tracing through a program with microsecond resolution and can actively be used to monitor drivers, interrupt handlers, operating system, or real-time application code that has critical time constraints.

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