Code

Add to the main application source file, outside of any functions:

struct usart_module usart_instance;

Copy-paste the following setup code to your user application:

void configure_usart(void)
{
    struct usart_config config_usart;
    usart_get_config_defaults(&config_usart);

    config_usart.baudrate    = 9600;
    config_usart.mux_setting = EDBG_CDC_SERCOM_MUX_SETTING;
    config_usart.pinmux_pad0 = EDBG_CDC_SERCOM_PINMUX_PAD0;
    config_usart.pinmux_pad1 = EDBG_CDC_SERCOM_PINMUX_PAD1;
    config_usart.pinmux_pad2 = EDBG_CDC_SERCOM_PINMUX_PAD2;
    config_usart.pinmux_pad3 = EDBG_CDC_SERCOM_PINMUX_PAD3;

    while (usart_init(&usart_instance,
            EDBG_CDC_MODULE, &config_usart) != STATUS_OK) {
    }

    usart_enable(&usart_instance);
}

Add to user application initialization (typically the start of main()):

configure_usart();