OUTB(2)             Linux Programmer's Manual             OUTB(2)

       outb, outw, outl, outsb, outsw, outsl - port output
       inb, inw, inl, insb, insw, insl - port input
       outb_p, outw_p, outl_p, inb_p, inw_p, inl_p - paused I/O

       This  family  of  functions  is  used to do low level port
       input and output.  They are primarily designed for  inter-
       nal kernel use, but can be used from user space, given the
       following information in addition to that given in outb(9)

       You  compile  with -O or -O2 or similar. The functions are
       defined as inline macros, and will not be  substituted  in
       without  optimization  enabled,  causing unresolved refer-
       ences at link time.

       You use ioperm(2) or alternatively  iopl(2)  to  tell  the
       kernel  to  allow the user space application to access the
       I/O ports in question. Failure to do this will  cause  the
       application to receive a segmentation fault.

       outb and friends are hardware specific. The port and value
       arguments are in the opposite order to most DOS  implemen-

       outb(9), ioperm(2), iopl(2)

Linux                   November 29, 1995                       1