Synchronizing Peripheral Operations with Timer Interrupts

Synchronizing Peripheral Operations with Timer Interrupts

In this lesson, you will learn how to use timer interrupts to trigger periodic tasks like sensor sampling at precise intervals without stalling your main program.

The Problem with Polling

So far, you’ve learned how to create delays using timers. If you want to sample a temperature sensor every 100 milliseconds, you might be tempted to use a loop that waits:

while(1) {
    read_sensor();
    delay_ms(100); // Blocks the CPU!
}

The issue here is "blocking." While the CPU is waiting in that delay_ms() function, it cannot perform other critical tasks like processing user input or communication. This is inefficient for real-time systems.

The Interrupt Solution

Instead of waiting, we can configure our hardware timer to "interrupt" the CPU exactly when the time interval expires. By enabling the Timer Update Interrupt, the hardware tracks the time for you. When the timer counter reaches the value stored in your Auto-Reload Register, the hardware automatically pauses your main() loop, jumps to a special function called an Interrupt Service Routine (ISR), executes your task, and then returns to what it was doing.

This effectively offloads the "timing" to the hardware timer peripheral. Your main() loop remains free to run other code, and your sensor sampling happens at the exact same frequency regardless of how long the rest of your program takes to execute.

Practical Implementation

To set this up, you must:

1. Configure your Timer Prescaler and Auto-Reload Register to define your target frequency.
2. Enable the Timer Update Interrupt in the interrupt controller.
3. Define the ISR function (e.g., TIM_IRQHandler) where you place your sensor reading code.

void TIM_IRQHandler(void) {
    if (timer_is_update_event()) {
        read_sensor(); // Performed exactly every 100ms
        clear_interrupt_flag();
    }
}

By leveraging hardware interrupts, you ensure your timing is precise and your main() loop stays responsive and non-blocking.

Key Takeaway: Using hardware timer interrupts allows your system to perform time-sensitive tasks at exact intervals while keeping the main loop free for other operations.