Configure DMA

Create a callback function of receiver done.

static void transfer_done_rx(struct dma_resource* const resource )
{
    dma_start_transfer_job(&usart_dma_resource_tx);
}

Create a callback function of transmission done.

static void transfer_done_tx(struct dma_resource* const resource )
{
    dma_start_transfer_job(&usart_dma_resource_rx);
}

Create a DMA resource configuration structure, which can be filled out to adjust the configuration of a single DMA transfer.

struct dma_resource_config config;

Initialize the DMA resource configuration struct with the module's default values.

dma_get_config_defaults(&config);

Set extra configurations for the DMA resource. It is using peripheral trigger. SERCOM TX empty trigger causes a beat transfer in this example.

config.peripheral_trigger = EDBG_CDC_SERCOM_DMAC_ID_RX;
config.trigger_action = DMA_TRIGGER_ACTON_BEAT;

Allocate a DMA resource with the configurations.

dma_allocate(resource, &config);

Create a DMA transfer descriptor configuration structure, which can be filled out to adjust the configuration of a single DMA transfer.

struct dma_descriptor_config descriptor_config;

Initialize the DMA transfer descriptor configuration struct with the module's default values.

dma_descriptor_get_config_defaults(&descriptor_config);

Set the specific parameters for a DMA transfer with transfer size, source address, and destination address.

descriptor_config.beat_size = DMA_BEAT_SIZE_HWORD;
descriptor_config.src_increment_enable = false;
descriptor_config.block_transfer_count = BUFFER_LEN;
descriptor_config.destination_address =
        (uint32_t)string + sizeof(string);
descriptor_config.source_address =
        (uint32_t)(&usart_instance.hw->USART.DATA.reg);

Create the DMA transfer descriptor.

dma_descriptor_create(descriptor, &descriptor_config);

Create a DMA resource configuration structure for TX, which can be filled out to adjust the configuration of a single DMA transfer.

struct dma_resource_config config;

Initialize the DMA resource configuration struct with the module's default values.

dma_get_config_defaults(&config);

Set extra configurations for the DMA resource. It is using peripheral trigger. SERCOM RX Ready trigger causes a beat transfer in this example.

config.peripheral_trigger = EDBG_CDC_SERCOM_DMAC_ID_TX;
config.trigger_action = DMA_TRIGGER_ACTON_BEAT;

Allocate a DMA resource with the configurations.

dma_allocate(resource, &config);

Create a DMA transfer descriptor configuration structure, which can be filled out to adjust the configuration of a single DMA transfer.

struct dma_descriptor_config descriptor_config;

Initialize the DMA transfer descriptor configuration struct with the module's default values.

dma_descriptor_get_config_defaults(&descriptor_config);

Set the specific parameters for a DMA transfer with transfer size, source address, and destination address.

descriptor_config.beat_size = DMA_BEAT_SIZE_HWORD;
descriptor_config.dst_increment_enable = false;
descriptor_config.block_transfer_count = BUFFER_LEN;
descriptor_config.source_address = (uint32_t)string + sizeof(string);
descriptor_config.destination_address =
    (uint32_t)(&usart_instance.hw->USART.DATA.reg);

Create the DMA transfer descriptor.

dma_descriptor_create(descriptor, &descriptor_config);