outb (2)

Leading comments

Copyright (c) 1995 Paul Gortmaker
(gpg109@rsphy1.anu.edu.au)
Wed Nov 29 10:58:54 EST 1995

%%%LICENSE_START(GPLv2+_DOC_FULL)
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

The GNU General Public License's references to "object code"
and "executables" are to be interpreted as the output of any
document for...

(The comments found at the beginning of the groff file "man2/outb.2".)

NAME

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

SYNOPSIS

#include <sys/io.h>

unsigned char inb(unsigned short int port);
unsigned char inb_p(unsigned short int port);
unsigned short int inw(unsigned short int port);
unsigned short int inw_p(unsigned short int port);
unsigned int inl(unsigned short int port);
unsigned int inl_p(unsigned short int port);

void outb(unsigned char value, unsigned short int port);
void outb_p(unsigned char value, unsigned short int port);
void outw(unsigned short int value, unsigned short int port);
void outw_p(unsigned short int value, unsigned short int port);
void outl(unsigned int value, unsigned short int port);
void outl_p(unsigned int value, unsigned short int port);

void insb(unsigned short int port, void *addr,
           unsigned long int count);
void insw(unsigned short int port, void *addr,
           unsigned long int count);
void insl(unsigned short int port, void *addr,
           unsigned long int count);
void outsb(unsigned short int port, const void *addr,
           unsigned long int count);
void outsw(unsigned short int port, const void *addr,
           unsigned long int count);
void outsl(unsigned short int port, const void *addr,
           unsigned long int count);

DESCRIPTION

This family of functions is used to do low-level port input and output. The out* functions do port output, the in* functions do port input; the b-suffix functions are byte-width and the w-suffix functions word-width; the _p-suffix functions pause until the I/O completes.

They are primarily designed for internal kernel use, but can be used from user space.
You must 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 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.

CONFORMING TO

outb() and friends are hardware-specific. The value argument is passed first and the port argument is passed second, which is the opposite order from most DOS implementations.

SEE ALSO

ioperm(2), iopl(2)

COLOPHON

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