1.17.6 Direct Memory Access Controller (DMAC)

The Direct Memory Access (DMA) Controller is a bus master module useful for data transfers between different devices without CPU intervention. The source and destination of a DMA transfer can be any of the memory mapped modules existent in the device such as SPI, UART, PMP, etc., or memory itself.

The DMA Controller can also be used to generate CRC on the data been transferred through the channel.

Using The Library

User can use either callback mechanism or polling mechanism to determine DMA transfer 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     (U1TXREG)

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_1, DMAC_Callback, 0);

      DMAC_ChannelTransfer(DMAC_CHANNEL_1, txBuffer, sizeof(txBuffer), (const void *)USART1_TRANSMIT_ADDRESS, 1, 1);

}

Polling method

This example demonstrates DMA transfer with polling

#define USART1_TRANSMIT_ADDRESS     (&U1TXREG)

uint8_t txBuffer[] = "Hello World!";

int main ( void )
{
      SYS_Initialize ( NULL );

      DMAC_ChannelTransfer(DMAC_CHANNEL_1, txBuffer, sizeof(txBuffer), (const void *)USART1_TRANSMIT_ADDRESS, 1, 1);

      while(DMAC_ChannelIsBusy(DMAC_CHANNEL_1));
}

Library Interface

peripheral library provides the following interfaces:

Functions


Name	Description
DMAC_Initialize	This function initializes the DMAC controller of the device
DMAC_ChannelCallbackRegister	This function allows a DMAC PLIB client to set an event handler
DMAC_ChannelTransfer	Schedules a DMA transfer on the specified DMA channel
DMAC_ChainTransferSetup	Setup a DMA channel for chain transfer
DMAC_ChannelPatternMatchSetup	Sets up DMA channel for pattern matching
DMAC_ChannelPatternMatchDisable	Disables the DMA pattern matching
DMAC_ChannelDisable	This function disables the DMA channel
DMAC_ChannelIsBusy	Reads the busy status of a channel
DMAC_ChannelTransferStatusGet	Returns the DMA channel's transfer status
DMAC_ChannelCRCSetup	DMA Channel CRC setup and enable function
DMAC_CRCDisable	DMA CRC disable function
DMAC_CRCRead	DMA CRC read function

Data types and constants


Name	Type	Description
DMAC_ERROR	Enum	Identifies the available DMA operating modes
DMAC_TRANSFER_EVENT	Enum	Identifies the status of the transfer event
DMAC_CHANNEL_CALLBACK	Typedef	Pointer to a DMAC Transfer Event handler function
DMAC_CHANNEL	Enum	Fundamental data object that represents DMA channel number
DMAC_CRC_SETUP	Struct	Fundamental data object that represents DMA CRC setup parameters