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outb
<html> <head> <title>outb</title> <META NAME="KEYWORDS" CONTENT="outb"> </head> <body BGCOLOR="#ffffff" LINK="#0000ff" VLINK="#0000ff" ALINK="#0000ff" TEXT="#000000"> <center> <h1><b>outb</b></h1></center> <PRE> <STRONG><A HREF="/man2/OUTB">OUTB(2)</A></STRONG> Linux Programmer's Manual <STRONG><A HREF="/man2/OUTB">OUTB(2)</A></STRONG> 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 <STRONG><A HREF="/man2/ioperm">ioperm(2)</A></STRONG> or alternatively <STRONG><A HREF="/man2/iopl">iopl(2)</A></STRONG> to tell the kernel to allow the user space application to access the I/O ports in question. Fail- ure 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 or- der from most DOS implementations. SEE ALSO <STRONG><A HREF="/man2/ioperm">ioperm(2)</A></STRONG>, <STRONG><A HREF="/man2/iopl">iopl(2)</A></STRONG> COLOPHON This page is part of release 5.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 <STRONG><A HREF="/man2/OUTB">OUTB(2)</A></STRONG></PRE> <center> <h6>Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2025 <a href="http://www.he.net">Hurricane Electric</a>. All Rights Reserved.</h6></center> </body> </html>