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

       This page is part of release 4.15 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/.