How to Use DMA with ADC in Embedded C: Simple Guide

To use DMA with ADC in embedded C, configure the ADC to trigger conversions and set up the DMA controller to automatically transfer ADC data to memory. This offloads the CPU by handling data movement in the background, improving efficiency and speed.

Syntax

The basic steps to use DMA with ADC in embedded C include:

• Initialize the ADC peripheral to start conversions.
• Configure the DMA controller with source (ADC data register) and destination (memory buffer) addresses.
• Set the number of data items to transfer.
• Enable DMA requests from the ADC.
• Start ADC conversions and DMA transfers.

This setup allows ADC data to be moved to memory automatically without CPU intervention.

c

/* Pseudocode syntax for ADC with DMA setup */
ADC_Init(); // Initialize ADC
DMA_Init(); // Initialize DMA
DMA_SetSourceAddress(&ADC->DR); // ADC data register
DMA_SetDestinationAddress(buffer); // Memory buffer
DMA_SetDataLength(buffer_size); // Number of samples
ADC_EnableDMARequest(); // Enable ADC DMA request
DMA_Enable(); // Enable DMA transfer
ADC_StartConversion(); // Start ADC conversions

Example

This example shows how to configure ADC with DMA on a generic microcontroller using embedded C. It reads 10 ADC samples into a buffer automatically.

c

#include <stdint.h>
#include <stdbool.h>

#define ADC_DATA_REGISTER (*(volatile uint16_t*)0x4001204C) // Example ADC data register address
#define DMA_CHANNEL_ENABLE (1 << 0)

volatile uint16_t adc_buffer[10];

void ADC_Init(void) {
    // Configure ADC settings (clock, channel, resolution)
    // This is hardware-specific and simplified here
}

void DMA_Init(void) {
    // Configure DMA source and destination addresses
    // Set source to ADC data register
    // Set destination to adc_buffer
    // Set number of data items to 10
}

void ADC_EnableDMARequest(void) {
    // Enable ADC to generate DMA requests on conversion complete
}

void ADC_StartConversion(void) {
    // Start ADC conversions (continuous or single)
}

void DMA_Enable(void) {
    // Enable DMA channel to start transfer
}

int main(void) {
    ADC_Init();
    DMA_Init();
    ADC_EnableDMARequest();
    DMA_Enable();
    ADC_StartConversion();

    // Wait or do other tasks while DMA fills adc_buffer

    while(1) {
        // Main loop
    }

    return 0;
}

Common Pitfalls

• Not enabling DMA requests in ADC: The ADC must be configured to trigger DMA transfers; otherwise, DMA won't start.
• Incorrect DMA source or destination addresses: Using wrong addresses causes data corruption or no transfer.
• Not setting the correct data length: DMA needs the exact number of items to transfer to stop properly.
• Forgetting to enable DMA channel: DMA must be enabled after configuration to start working.
• Buffer size mismatch: Ensure the buffer size matches the DMA transfer length to avoid overflow.

c

/* Wrong way: Missing ADC DMA request enable */
ADC_Init();
DMA_Init();
// ADC_EnableDMARequest(); // Forgot this step
DMA_Enable();
ADC_StartConversion();

/* Right way: */
ADC_Init();
DMA_Init();
ADC_EnableDMARequest(); // Correctly enable DMA requests
DMA_Enable();
ADC_StartConversion();

Quick Reference

Remember these key points when using DMA with ADC:

• Configure ADC to generate DMA requests on conversion complete.
• Set DMA source to ADC data register and destination to memory buffer.
• Set correct data length for DMA transfer.
• Enable DMA channel before starting ADC conversions.
• Use interrupts or polling to know when DMA transfer completes if needed.

Key Takeaways

Enable ADC DMA requests to allow automatic data transfer.

Set DMA source to ADC data register and destination to a memory buffer.

Configure the correct number of data items for DMA transfer.

Always enable the DMA channel after configuration.

Check for common mistakes like missing DMA enable or wrong addresses.