I need help with serial driver

[.]

        Greetings!
I did not find in "BSD Developers handbook" or anywhere else theese
precious bits of information:
1. What methods should character driver ( /dev/cuaa or similar) have?
2. How application requests (open/read/ioctl/etc.) are mapped to
methods of the driver?
3. Are there any special functions besides generic file I/O operations
(apart from ioctl(2))? Or are there any "special cases" of ioctl apart
from what is covered by man page?

I need to utlize the abilities of /dev/cuua to their extreme, but I
do not want to rewrite the standard one.

Sorry for troubling you,

      Igor