I have followed the ASF samples to configure my USART module in SAM V71 on Xplained Ultra EV kit.
However, the actual baudrate is always half of what I configure.
#define USART_SITALL_OUT_SERIAL USART0
#define USART_SITALL_OUT_SERIAL_ID ID_USART0
#define USART_SITALL_OUT_SERIAL_ISR_HANDLER USART0_Handler
#define USART_SITALL_OUT_SERIAL_BAUDRATE 9600
#define USART_SITALL_OUT_SERIAL_CHAR_LENGTH US_MR_CHRL_8_BIT
#define USART_SITALL_OUT_SERIAL_PARITY US_MR_PAR_NO
#define USART_SITALL_OUT_SERIAL_STOP_BIT US_MR_NBSTOP_1_BIT
#define USART_SITALL_OUT_SERIAL_IRQn USART0_IRQn
usart_init_rs232(USART_SITALL_OUT_SERIAL, &usart_sitall_out_settings, sysclk_get_main_hz());
I think this is a pretty standard USART configuration. However, every time I write to USART TXD line, the actual baudrate is 4800. If I change the USART config to run at 19200, it will run at 9600 etc.