Workflow

Enable global interrupts, so that the callbacks can be fired.

system_interrupt_enable_global();

Send a string to the USART to show the demo is running, blocking until all characters have been sent.

uint8_t string[] = "Hello World!\r\n";
usart_write_buffer_wait(&usart_instance, string, sizeof(string));

Enter an infinite loop to continuously echo received values on the USART.

while (true) {

Perform an asynchronous read of the USART, which will fire the registered callback when characters are received.

usart_read_buffer_job(&usart_instance,
        (uint8_t *)rx_buffer, MAX_RX_BUFFER_LENGTH);