Tick timer and scheduler in FreeRTOS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the role of the tick timer in FreeRTOS?

The tick timer generates regular interrupts at a fixed frequency. These interrupts allow FreeRTOS to keep track of time and manage task switching.

beginner

How does the FreeRTOS scheduler decide which task to run next?

The scheduler selects the highest priority task that is ready to run. If multiple tasks have the same priority, it uses time slicing or round-robin to share CPU time.

intermediate

What happens during a tick interrupt in FreeRTOS?

During a tick interrupt, FreeRTOS updates its internal tick count and checks if any tasks need to be switched based on their state and priority.

intermediate

Why is the tick rate important in FreeRTOS?

The tick rate determines how often the scheduler runs and how precise timing functions are. A higher tick rate means more frequent task switching but more CPU overhead.

intermediate

Explain the difference between preemptive and cooperative scheduling in FreeRTOS.

Preemptive scheduling allows the scheduler to interrupt a running task to switch to a higher priority task. Cooperative scheduling requires tasks to yield control voluntarily.

What triggers the FreeRTOS scheduler to run?

A A button press

B A tick timer interrupt

C A network packet arrival

D A manual function call only

The tick timer interrupt triggers the scheduler to check if a task switch is needed.

What does the tick timer frequency affect?

A The CPU clock speed

B The size of the memory

C The number of tasks allowed

D How often tasks can be switched

The tick timer frequency controls how often the scheduler runs and can switch tasks.

In preemptive scheduling, when can a task be interrupted?

A Only when it finishes

B Only when it yields

C When a higher priority task becomes ready

D Never

Preemptive scheduling allows interruption when a higher priority task is ready.

What is the main purpose of the FreeRTOS scheduler?

A To decide which task runs and when

B To manage memory allocation

C To handle input/output devices

D To compile code

The scheduler manages task execution order based on priority and readiness.

What happens if the tick rate is set too high?

A CPU overhead increases due to frequent interrupts

B Tasks run slower

C Memory usage decreases

D Scheduler stops working

A very high tick rate causes more CPU time spent handling interrupts, reducing efficiency.

Describe how the tick timer and scheduler work together in FreeRTOS to manage tasks.

Think about what happens every time the tick timer interrupts.

Explain the difference between preemptive and cooperative scheduling in FreeRTOS and how the tick timer affects them.

Consider how tasks lose control in each scheduling type.