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

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

       void insb(unsigned short port, void *addr,
                  unsigned long count);
       void insw(unsigned short port, void *addr,
                  unsigned long count);
       void insl(unsigned short port, void *addr,
                  unsigned long count);
       void outsb(unsigned short port, const void *addr,
                  unsigned long count);
       void outsw(unsigned short port, const void *addr,
                  unsigned long count);
       void outsl(unsigned short port, const void *addr,
                  unsigned long 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 5.10 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/.