1.30.5 Direct Memory Access Controller (DMAC)

Using The Library

DMA controller requires source address, destination address and transfer count to initiate transfer. It transfers data on each DMA trigger and decrements the transfer count. The DMA generates completion interrupt to notify CPU at the end of the DMA transfer.

User can use either callback mechanism or polling mechanism to determine DMA completion.

• With polling, the application will need to continuously poll to check if the DMA has completed the transfer.

• With callback, the registered callback function will be called when the transfer is completed. This means the application do not have to poll continuously.

Callback method

This example demonstrates DMA transfer with callback

#define USART1_TRANSMIT_ADDRESS     (&SERCOM4_REGS->USART.DATA)

uint8_t txBuffer[] = "Hello World!";

void DMAC_Callback(DMAC_TRANSFER_EVENT status, uintptr_t context)
{
      if(status == DMAC_TRANSFER_EVENT_COMPLETE)
      {
           // Transfer is completed.
      }
}

 int main ( void )
{
      SYS_Initialize ( NULL );

      DMAC_ChannelCallbackRegister(DMAC_CHANNEL_0, DMAC_Callback, 0);

      DMAC_ChannelTransfer(DMAC_CHANNEL_0, txBuffer, (const void *)USART1_TRANSMIT_ADDRESS, sizeof(txBuffer));

}

Polling method

This example demonstrates DMA transfer with polling

#define USART1_TRANSMIT_ADDRESS     (&SERCOM4_REGS->USART.DATA)

uint8_t txBuffer[] = "Hello World!";

int main ( void )
{
      SYS_Initialize ( NULL );

      DMAC_ChannelTransfer(DMAC_CHANNEL_0, txBuffer, (const void *)USART1_TRANSMIT_ADDRESS, sizeof(txBuffer));

      while(DMAC_ChannelIsBusy(DMAC_CHANNEL_0));
}

Library Interface

Direct Memory Access Controller peripheral library provides the following interfaces:

Functions

Data types and constants