[Asterisk-Dev] zaptel API description?

[Bob Smith]

Hi
    I would like to better understand the Linux
device drivers used by Asterisk.  Is the zaptel
API documented anywhere?  I'm interested in the
ioctl()'s as well as the meaning of data read
and written to each of the zaptel entries in the
/dev directory.

Any help or pointers to docs or *simple* working
code would be really appreciated.

My first project would be to use my old X100P
board as a simple answering machine with caller
ID.

thanks in advance
Bob Smith