In this lesson, you will learn how to diagnose race conditions and stack overflows caused by nested interrupts using logic analyzers and hardware breakpoints.
When you enable nested interrupts, a higher-priority interrupt can preempt a lower-priority one. While this improves responsiveness, it introduces the danger of a "race condition"—where shared data is accessed by multiple contexts simultaneously—and stack overflows, where the cumulative stack usage of nested ISRs exceeds your memory allocation.
Identifying Race Conditions with Logic Analyzers
A race condition often occurs when the main loop and an ISR attempt to modify the same variable, or when a low-priority ISR is interrupted by a high-priority one that accesses the same resource. To debug this, use a logic analyzer to toggle specific GPIO pins at the start and end of your critical code sections.
If you observe an unexpected signal pattern—such as an interrupt signal overlapping with a data-processing block that shouldn't be interrupted—you have identified a race condition. By setting a hardware breakpoint on the memory address of the shared variable, the processor will halt the exact moment a write occurs. This allows you to inspect the stack trace and verify if an interrupt triggered at an illegal time.
Debugging Stack Overflows
Nested interrupts behave like a stack of plates; each entry consumes space for the CPU context (registers, program counter). If your nesting depth is too high, you will eventually overwrite adjacent memory.
To detect this, set a hardware breakpoint on the memory address immediately preceding your stack’s base (the "Stack Guard"). If the CPU hits this breakpoint, you know the stack pointer has ventured into forbidden territory.
// Example: Debugging a shared variable with a hardware breakpoint
volatile uint32_t shared_sensor_data;
void High_Priority_ISR(void) {
// Hardware breakpoint here catches concurrent access
shared_sensor_data = read_adc();
}
void Mainline_Task(void) {
__disable_irq(); // Prevent race condition
process(shared_sensor_data);
__enable_irq();
}
By correlating hardware breakpoints with physical logic analyzer traces, you can pinpoint whether your system crashed due to data corruption or stack exhaustion during a high-load interrupt event.
Key Takeaway: Use hardware breakpoints to catch illegal memory access and logic analyzers to visualize execution timing, ensuring your interrupt nesting logic remains predictable and safe.