Common RTOS bugs and debugging strategies in FreeRTOS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a common cause of priority inversion in RTOS?

Priority inversion happens when a low-priority task holds a resource needed by a higher-priority task, causing the high-priority task to wait and potentially miss deadlines.

beginner

How can deadlocks occur in an RTOS environment?

Deadlocks occur when two or more tasks wait indefinitely for resources held by each other, creating a cycle of dependencies that stops all involved tasks.

intermediate

What debugging strategy helps identify stack overflow in FreeRTOS tasks?

Using FreeRTOS's stack overflow hook function allows detection when a task exceeds its stack size, helping to catch stack overflow bugs early.

intermediate

Why is using trace tools important in debugging RTOS applications?

Trace tools record task switches, interrupts, and events in real-time, helping developers understand system behavior and find timing or synchronization bugs.

beginner

What is a common symptom of race conditions in RTOS tasks?

Race conditions cause unpredictable behavior like corrupted data or crashes because multiple tasks access shared data without proper synchronization.

Which of the following is a typical cause of deadlock in RTOS?

A A task with too high priority

B A task running out of stack space

C A task that never yields

D Two tasks waiting on each other's resources

Deadlock happens when tasks wait on each other’s resources, creating a cycle that stops progress.

What does FreeRTOS's stack overflow hook function do?

A Detects when a task uses more stack than allocated

B Prevents priority inversion automatically

C Logs all task switches

D Resets the system on error

The stack overflow hook is called when a task exceeds its stack size, helping catch stack overflow bugs.

Priority inversion can be avoided by:

A Increasing all task priorities

B Using priority inheritance protocols

C Disabling interrupts

D Using larger stack sizes

Priority inheritance temporarily raises the priority of the low-priority task holding a resource to avoid blocking high-priority tasks.

Which tool helps visualize task execution and timing in FreeRTOS?

A Tracealyzer

B GDB

C Valgrind

D Wireshark

Tracealyzer is a trace tool that shows task switches and timing, useful for debugging RTOS behavior.

Race conditions occur when:

A The scheduler is disabled

B A task runs out of stack

C Multiple tasks access shared data without synchronization

D A task has too low priority

Race conditions happen when tasks access shared data at the same time without proper locks or synchronization.

Explain what causes priority inversion in an RTOS and how it can be mitigated.

Think about tasks waiting for resources and how priorities can change temporarily.

Describe common debugging strategies to find and fix deadlocks in FreeRTOS applications.

Consider how tasks wait for resources and how to detect cycles.