Getting OUT from C

[James E. Mower]

I'm trying to write to an internal port within the AT running under
XENIX.  Unfortunately, I don't know enough assembler to get to the 
OUT function directly (I keep getting segmentation faults when I try
to write to port 991 (decimal)) so I am looking for a comparable way
to get to it from the C compiler under XENIX.  Can anyone tell me how
this might be done?  Thanks in advance.