PendSV and SysTick exceptions in ARM Architecture - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the purpose of PendSV exception

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

A To perform context switching in an operating system

B To reset the processor after a fault

C To manage external hardware interrupts

D To handle system timer interrupts for task scheduling

💡 Hint

Think about which exception is used for switching between tasks in an OS.

PendSV is designed to trigger context switches in an OS by allowing deferred interrupt handling, making it ideal for task switching.

📋 Factual

intermediate

SysTick exception timer source

Which clock source is typically used by the SysTick timer in ARM Cortex-M processors?

A External oscillator clock

B Real-time clock (RTC)

C Processor clock (core clock)

D Watchdog timer clock

💡 Hint

SysTick is designed to provide a regular interrupt based on the CPU speed.

The SysTick timer usually uses the processor's core clock to generate periodic interrupts for system timing.

🔍 Analysis

advanced

Effect of PendSV priority on system behavior

What happens if the PendSV exception priority is set higher than the SysTick exception priority in an ARM Cortex-M system?

A SysTick will always preempt PendSV regardless of priority

B PendSV will preempt SysTick, possibly delaying system tick handling

C Both exceptions will run simultaneously without preemption

D PendSV will be disabled automatically by the processor

💡 Hint

Consider how interrupt priorities affect which exception runs first.

In ARM Cortex-M, a higher priority exception can preempt a lower priority one. If PendSV has higher priority, it can interrupt SysTick, delaying its handling.

❓ Comparison

advanced

Difference between PendSV and SysTick exceptions

Which statement correctly distinguishes PendSV from SysTick exceptions?

A SysTick is a fixed priority exception; PendSV priority is programmable

B PendSV is triggered by hardware timer; SysTick is software triggered

C PendSV is a programmable system timer; SysTick is used for context switching

D SysTick generates periodic interrupts; PendSV is used for deferred interrupt handling

💡 Hint

Think about the typical use cases of each exception.

SysTick generates regular timer interrupts for system ticks, while PendSV is used to defer interrupt handling, often for context switching.

❓ Reasoning

expert

Determining the number of SysTick interrupts in a time interval

An ARM Cortex-M processor runs at 48 MHz. The SysTick timer is configured with a reload value of 47999. How many SysTick interrupts occur in one second?

A 1000 interrupts

B 480 interrupts

C 1 interrupt

D 48 interrupts

💡 Hint

Calculate the timer tick frequency and how often the reload value triggers an interrupt.

SysTick counts down from 47999 to 0 at 48 MHz clock, so interrupt frequency = 48,000,000 / (47999 + 1) = 1000 Hz, meaning 1000 interrupts per second.