Receive data via USART on Atmel SAMD20
Did you fix this? It would be great if you could include the complete code you are using. 
In case you didnt, try putting your usart initialization inside a while cycle. 

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


The usart needs some time to complete the initialization process, if you dont use that, it will always fail in the first try. 
Remember to replace EDBG_CDC_MODULE with the SERCOM you are using in your project