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 primar-
ily designed for internal kernel use, but can be used from user space.
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 references at
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 appli-
cation to receive a segmentation fault.
outb and friends are hardware specific. The port and value arguments are in the opposite
order to most DOS implementations.
Linux 1995-11-29 OUTB(2)