asynchronous use

Looking at the code in ad_uart.c I can see the following:

void ad_uart_write_async(uart_device dev, const char *wbuf, size_t wlen, ad_uart_user_cb cb,
void *user_data)
{
uart_device_config *device = (uart_device_config *) dev;
uart_bus_dynamic_data *data = device->bus_data;