RTOS Concepts

Question 1

What problems does RTOS solve?

Answer 1

• Task scheduling
• Timing precision
• Concurrency
• Resource sharing
• Predictability
• synchronisation

Question 2

Tasks vs threads

Answer 2

• both are concurrent process
• threads are managed by the operating system
• task is high-level and managed by a runtime environment

Question 3

What is priority inversion?

Answer 3

When a low-priority task is blocking a high-priority task
- priority inheritance is used to fix it

Question 4

Mutex vs Semaphore

Answer 4

Mutex: exclusive resource locking.
- A thread or a task locks the mutex before going into a critical section
- unlocks the mutex when done indicating to other threads the critical section is available

Semaphore: signalling or counting; often used between ISR and task communication
- used for both synchronisation and mutual exclusion

Question 5

What happens if an ISR takes too long?

Answer 5

• starves other processes of processing time
• system mis real-time deadlines, which can be fatal if the system has to meet hard real-time deadlines such as in safety critical systems
• cause miss processing of interrupts

Question 6

How do queues work?

Answer 6

Tasks or ISRs can put data into queues and you can communicate that queue to other tasks