PendSV and SysTick exceptions in ARM Architecture - Mini Project: Build & Apply

Understanding PendSV and SysTick Exceptions in ARM Architecture

📖 Scenario: You are learning about ARM Cortex processors and how they handle special system events called exceptions. Two important exceptions are PendSV and SysTick. These help the processor manage tasks and keep time.Imagine you are building a simple system that uses these exceptions to switch tasks and keep track of time.

🎯 Goal: Create a basic setup that defines the PendSV and SysTick exceptions, configure a timer for SysTick, and write simple handlers to understand how these exceptions work together in ARM Cortex processors.

📋 What You'll Learn

Define the PendSV exception handler function named PendSV_Handler

Define the SysTick exception handler function named SysTick_Handler

Create a variable tick_count to count SysTick interrupts

Configure the SysTick timer with a reload value of 1000

Enable the SysTick timer and its interrupt

💡 Why This Matters

🌍 Real World

PendSV and SysTick exceptions are used in real-time operating systems on ARM Cortex processors to manage task switching and system timing.

💼 Career

Understanding these exceptions is important for embedded systems developers working on ARM Cortex microcontrollers, especially in firmware and RTOS development.

1

Define the PendSV and SysTick exception handlers

Write two empty functions named PendSV_Handler and SysTick_Handler to represent the PendSV and SysTick exception handlers.

ARM Architecture

# Define the PendSV_Handler function
# Define the SysTick_Handler function
# Your code here

Need a hint?

Use the exact function names PendSV_Handler and SysTick_Handler with void return type and no parameters.

2

Create a tick counter variable

Declare a global variable named tick_count of type unsigned int and initialize it to 0. This will count the number of SysTick interrupts.

ARM Architecture

void PendSV_Handler(void) {
    // PendSV exception handler code will go here
}

void SysTick_Handler(void) {
    // SysTick exception handler code will go here
}

// Declare tick_count variable
# Your code here

Need a hint?

Use unsigned int tick_count = 0; exactly as shown.

3

Implement SysTick_Handler to increment tick_count

Inside the SysTick_Handler function, add code to increase the tick_count variable by 1 each time the SysTick exception occurs.

ARM Architecture

unsigned int tick_count = 0;

void PendSV_Handler(void) {
    // PendSV exception handler code will go here
}

void SysTick_Handler(void) {
    // Increment tick_count here
    # Your code here
}

Need a hint?

Inside SysTick_Handler, write tick_count++; to increase the counter.

4

Configure and enable the SysTick timer

Write code to set the SysTick reload value to 1000, clear the current value, and enable the SysTick timer with its interrupt. Use the exact variable names SysTick->LOAD, SysTick->VAL, and SysTick->CTRL. Set SysTick->CTRL to 0x07 to enable the timer, its interrupt, and the processor clock.

ARM Architecture

unsigned int tick_count = 0;

void PendSV_Handler(void) {
    // PendSV exception handler code will go here
}

void SysTick_Handler(void) {
    tick_count++;
}

// Configure SysTick timer
# Your code here

Need a hint?

Set SysTick->LOAD to 1000, clear SysTick->VAL, and set SysTick->CTRL to 0x07 to enable timer, interrupt, and clock.