The current type of the defined bitfields is *mut u8, a pointer type. It is not clear to me how they are supposed to be used like that. I would expect the bitmasks to be used, e.g., as:

unsafe {
    *UCSRB = TXEN | RXEN | RXCIE;
}

That doesn't work with pointers, though. I've found a workaround using core::intrinsics::transmute, casting it to an usize and subsequently cropping the value to an u8. But I really think that it is a bug in this library.

Do you agree? If so, I might take the time to create a PR to fix the issue.