Retrieve I/O descriptor.
int32_t usart_dma_get_io_descriptor( struct usart_dma_descriptor *const descr, struct io_descriptor ** io )
This function retrieves the I/O descriptor of the given USART descriptor.
Type: struct usart_dma_descriptor Struct *const
A USART descriptor which is used to communicate via USART
Type: struct io_descriptor Struct **
An I/O descriptor to retrieve
Type: int32_t
The status of I/O descriptor retrieving.