Implementing ADC End-of-Conversion Interrupt Handling

Implementing ADC End-of-Conversion Interrupt Handling

In this lesson, you will learn how to transition from polling your Analog-to-Digital Converter (ADC) to an interrupt-driven model, allowing your processor to focus on other tasks until a conversion is ready.

The Problem with Polling

Up to this point, you have likely been triggering a conversion and then spinning in a while loop, waiting for a status bit to signal that the data is ready. This is known as "polling." While simple, it wastes valuable CPU cycles and introduces latency, as the processor cannot do anything else while it waits for the analog signal to be processed.

Event-Driven Architecture

An interrupt-driven approach allows the hardware to "tap the CPU on the shoulder" only when the data is ready. To implement this, we follow three steps:

1. Enable the Interrupt: Instead of just starting the ADC, you must set a specific bit in the ADC’s interrupt control register (often called ADC_IER or ADC_INTEN). This tells the hardware: "Once the conversion is complete, fire an interrupt signal to the CPU."
2. Configure the NVIC: The Nested Vectored Interrupt Controller (NVIC) acts as the bridge between the peripheral and the CPU. You must enable the specific interrupt vector associated with your ADC in the NVIC registers.
3. Define the ISR: You create an Interrupt Service Routine (ISR)—a function that the CPU automatically jumps to when the "End of Conversion" (EOC) signal arrives.

Practical Implementation

Inside your ISR, you perform the critical actions: read the value from the ADC data register, clear the interrupt pending flag (so the interrupt doesn’t fire again immediately), and store the result.

void ADC_IRQHandler(void) {
    // 1. Check if the interrupt was caused by End-of-Conversion
    if (ADC1->SR & ADC_SR_EOC) {
        // 2. Read the converted data
        uint16_t sensorValue = ADC1->DR;
        
        // 3. Clear the interrupt flag
        ADC1->SR &= ~ADC_SR_EOC;
        
        // 4. Process the data
        ProcessData(sensorValue);
    }
}

By offloading the "wait" time, your microcontroller can now execute complex logic or enter a low-power mode, waking up only when the ADC signal is finalized.

Key Takeaway: ADC end-of-conversion interrupts minimize latency and power consumption by allowing the CPU to respond asynchronously to analog events rather than wasting cycles polling status registers.