Quick Start Guide for the DMAC driver

This is the quick start guide for the SAM3A/3U/3X/4E DMA Controller (DMAC) Driver, with step-by-step instructions on how to configure and use the driver for a specific use case.

The code examples can be copied into the main application loop or any other function that will need to control the DMAC module.

Use Cases

• DMAC Basic Usage

DMAC Basic Usage

This use case will demonstrate how to initialize the DMAC module to perform a single memory to memory transfer.

Setup Steps

Prerequisites

This module requires the following service

• System Clock Management (sysclock)

Setup Code

Add these macros and global variable to the top of your application's C-file:

#define DMA_CH 0

#define DMA_BUF_SIZE    32

uint32_t g_dma_buf[6][DMA_BUF_SIZE];

Add this to the main loop or a setup function:

    pmc_enable_periph_clk(ID_DMAC);

Workflow

1. Define the variables needed, in order to perform a data transfer:

       uint32_t i;
       uint32_t cfg;
       dma_transfer_descriptor_t desc;

2. Prepare the data buffer to be transferred:

   
       for (i = 0; i < DMA_BUF_SIZE; i++) {
           g_dma_buf[0][i] = i;
           g_dma_buf[1][i] = 0;
       }

3. Initialize the DMAC module:

       dmac_init(DMAC);

4. Set the priority to round-robin:

       dmac_set_priority_mode(DMAC, DMAC_PRIORITY_ROUND_ROBIN);

5. Enable the DMAC module:

       dmac_enable(DMAC);

6. Configure the channel for:
   • Enable stop on done
   • Enable AHB protection
   • Set the FIFO so that largest defined length AHB burst is performed

     
         cfg = DMAC_CFG_SOD_ENABLE |        
                 DMAC_CFG_AHB_PROT(1) |     
                 DMAC_CFG_FIFOCFG_ALAP_CFG; 
         dmac_channel_set_configuration(DMAC, DMA_CH, cfg);

Usage Steps

Usage Code

Configure the DMA source and destination buffer addresses:

    desc.ul_source_addr = (uint32_t) g_dma_buf[0];
    desc.ul_destination_addr = (uint32_t) g_dma_buf[1];

Configure DMA CTRLA:

• Set the buffer transfer size to DMA_BUF_SIZE
• Set the source transfer width to 32-bit
• Set the destination transfer width to 32-bit

      desc.ul_ctrlA = DMAC_CTRLA_BTSIZE(DMA_BUF_SIZE) |
              DMAC_CTRLA_SRC_WIDTH_WORD |
              DMAC_CTRLA_DST_WIDTH_WORD;

  Configure DMA CTRLB:
• Disable source buffer descriptor fetch
• Disable destination buffer descriptor Fetch
• Enable memory-to-memory transfer
• Increment the source address
• Increment the destination address

      desc.ul_ctrlB = DMAC_CTRLB_SRC_DSCR_FETCH_DISABLE |
              DMAC_CTRLB_DST_DSCR_FETCH_DISABLE |
              DMAC_CTRLB_FC_MEM2MEM_DMA_FC |
              DMAC_CTRLB_SRC_INCR_INCREMENTING |
              DMAC_CTRLB_DST_INCR_INCREMENTING;

  Initialize the DMA transfer:

      desc.ul_descriptor_addr = 0;
      dmac_channel_single_buf_transfer_init(DMAC, DMA_CH, &desc);

  Start the DMA transfer:

      dmac_channel_enable(DMAC, DMA_CH);

  Finally, poll for the DMA transfer to complete:

      while (!dmac_channel_is_transfer_done(DMAC, DMA_CH)) {
      }