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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 3.78 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 http://www.kernel.org/doc/man-pages/.

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