PendSV and SysTick exceptions in ARM Architecture - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the PendSV exception in ARM Cortex-M processors?

PendSV (Pendable Service Call) is used to handle context switching in an operating system. It allows the processor to defer interrupt handling until it is safe to switch tasks.

beginner

What role does the SysTick exception play in ARM Cortex-M microcontrollers?

SysTick is a system timer exception used to generate periodic interrupts, often for creating time slices or system ticks in real-time operating systems.

intermediate

How does PendSV differ from SysTick in terms of priority and usage?

PendSV is usually set to the lowest priority to allow other interrupts to complete before a context switch, while SysTick typically has a higher priority to generate regular timing interrupts.

intermediate

Why is PendSV considered 'pendable' and how does this benefit task switching?

PendSV is 'pendable' because it can be triggered and delayed until all higher priority interrupts finish. This ensures that context switching happens safely without interrupting critical tasks.

beginner

What is a common use case for the SysTick timer in embedded systems?

SysTick is commonly used to create a regular time base for operating systems, such as generating ticks every millisecond to manage delays, timeouts, and scheduling.

What is the main function of the PendSV exception?

A To generate periodic timer interrupts

B To handle context switching in an OS

C To reset the processor

D To handle external interrupts

PendSV is designed to manage context switching by deferring the interrupt until safe to switch tasks.

Which exception is typically used to generate a regular system tick in ARM Cortex-M?

A PendSV

B HardFault

C SysTick

D NMI

SysTick is a dedicated timer exception used to generate periodic interrupts for system timing.

Why is PendSV usually assigned the lowest priority?

A To allow other interrupts to complete before switching tasks

B To speed up context switching

C To prevent it from ever running

D To handle critical faults first

PendSV runs last so that all higher priority interrupts finish before context switching.

What does the SysTick timer typically measure?

A Processor temperature

B External events

C Memory usage

D Elapsed time intervals

SysTick generates interrupts at fixed time intervals to measure elapsed time.

Which of these is true about PendSV?

A It can be pended and delayed until safe to run

B It resets the system

C It handles hardware faults

D It runs before all other interrupts

PendSV is designed to be pended and executed later, enabling safe context switching.

Explain the roles of PendSV and SysTick exceptions in ARM Cortex-M processors and how they work together in an operating system.

Think about task switching and timing in an OS.

Describe why PendSV is called a 'pendable' exception and how this feature helps in managing interrupts.

Consider interrupt priorities and safe task switching.