Memory-to-peripheral transfer in Embedded C

Introduction

Memory-to-peripheral transfer moves data from memory to a device like a screen or sensor. It helps send information without making the CPU do all the work.

Sending a picture stored in memory to a display screen.

Transferring audio data from memory to a speaker.

Sending sensor data stored in memory to a communication port.

Updating LED patterns by sending data from memory to LED controller.

Syntax

Embedded C

DMA_Channel->CCR = DMA_CCR_MINC | DMA_CCR_DIR | DMA_CCR_EN;
DMA_Channel->CPAR = (uint32_t)&PERIPHERAL_DATA_REGISTER;
DMA_Channel->CMAR = (uint32_t)memory_address;
DMA_Channel->CNDTR = data_length;

This example shows how to set up a DMA channel for memory-to-peripheral transfer.

DMA_CCR_DIR bit set means data moves from memory to peripheral.

Examples

Setup DMA to send data from memory buffer to USART1 data register for transmission.

Embedded C

DMA1_Channel3->CCR = DMA_CCR_MINC | DMA_CCR_DIR | DMA_CCR_EN;
DMA1_Channel3->CPAR = (uint32_t)&USART1->DR;
DMA1_Channel3->CMAR = (uint32_t)tx_buffer;
DMA1_Channel3->CNDTR = sizeof(tx_buffer);

Configure DMA to transfer 100 bytes from memory to SPI2 peripheral.

Embedded C

DMA2_Channel5->CCR = DMA_CCR_MINC | DMA_CCR_DIR | DMA_CCR_EN;
DMA2_Channel5->CPAR = (uint32_t)&SPI2->DR;
DMA2_Channel5->CMAR = (uint32_t)spi_tx_data;
DMA2_Channel5->CNDTR = 100;

Sample Program

This program sets up a DMA channel to send the string "Hello DMA!" from memory to the USART1 peripheral automatically. The CPU does not need to send each character.

Embedded C

#include <stdint.h>
#include "stm32f10x.h"  // Example MCU header

uint8_t message[] = "Hello DMA!";

void setup_dma_memory_to_peripheral(void) {
    // Enable clock for DMA1
    RCC->AHBENR |= RCC_AHBENR_DMA1EN;

    // Disable DMA channel before configuration
    DMA1_Channel4->CCR &= ~DMA_CCR_EN;

    // Set peripheral address (e.g., USART1 data register)
    DMA1_Channel4->CPAR = (uint32_t)&USART1->DR;

    // Set memory address
    DMA1_Channel4->CMAR = (uint32_t)message;

    // Set number of data to transfer
    DMA1_Channel4->CNDTR = sizeof(message) - 1; // exclude null terminator

    // Configure DMA channel:
    // Memory increment mode enabled
    // Direction: memory to peripheral
    // Enable transfer complete interrupt (optional)
    DMA1_Channel4->CCR = DMA_CCR_MINC | DMA_CCR_DIR | DMA_CCR_TCIE;

    // Enable DMA channel
    DMA1_Channel4->CCR |= DMA_CCR_EN;
}

int main(void) {
    // Setup USART1 here (not shown for simplicity)

    setup_dma_memory_to_peripheral();

    while (1) {
        // Main loop can do other tasks
    }
}

Important Notes

Memory-to-peripheral transfer is often done using DMA (Direct Memory Access) controllers.

Make sure the peripheral is ready to receive data before starting the transfer.

Always disable the DMA channel before changing its settings.

Summary

Memory-to-peripheral transfer moves data from memory to a device without CPU intervention.

DMA controllers handle this transfer efficiently.

Setup involves configuring source, destination, data size, and enabling the DMA channel.