Function uart_tx 

pub unsafe extern "C" fn uart_tx(
    dev: *const device,
    buf: *const u8,
    len: usize,
    timeout: i32,
) -> c_int

@brief Send given number of bytes from buffer through UART.

Function returns immediately and event handler, set using @ref uart_callback_set, is called after transfer is finished.

@param dev UART device instance. @param buf Pointer to transmit buffer. @param len Length of transmit buffer. @param timeout Timeout in microseconds. Valid only if flow control is enabled. @ref SYS_FOREVER_US disables timeout.

@return 0 on success, negative errno value on failure. @retval -ENOTSUP API is not enabled. @retval -EBUSY There is already an ongoing transfer.