inb man page

inb, outb, inw, outw, inl, outl — access I/O ports

Synopsis

inb ADDRESS
inw ADDRESS
inl ADDRESS
outb ADDRESS DATA
outw ADDRESS DATA
outl ADDRESS DATA

Examples

inb 0x278
outw 0x440 0xffff

Description

These commands enable command line and script access directly to I/O ports on PC hardware.

The "inb", "inw" and "inl" commands perform an input (read) operation on the given I/O port, and print the result.

The "outb", "outw" and "outl" commands perform an output (write) operation to the given I/O port, sending the given data. Note that the order of the parameters is ADDRESS DATA.

The size of the operation is selected according to the suffix, with "b" meaning byte, "w" meaning word (16 bits) and "l" meaning long (32 bits).

Port numbers are in the range 0-0xffff. We don't support access to memory mapped devices.

Hexadecimal numbers (prefixed by "0x"), decimal numbers, and octal numbers (prefixed by 0), are allowed as parameters.

Return from “in” Operations

The value read from the port by an "in" operation is normally printed in decimal.

Use the "--hex" option to print the result as hexadecimal ("0x" prefix is NOT printed).

Use the "--code" option to turn the result into an exit status. Note that Unix/shell can only reliably return exit status in the range 0-0x7f, so this is not particularly useful in practice.

Type and Size of Operation

The type and size of the operation is normally determined by the name of the command, eg. "inb" is a read operation of 1 byte.

You can override this by using the "--read", "--write" and/or "--size N" options. For "--size N", "N" should be 1, 2 or 4 meaning byte, word and long respectively.

Permissions

You would normally need to be root or have the "CAP_SYS_RAWIO" capability in order to run these commands.

Warning

Using these commands can cause Bad Things to happen to your hardware.

See Also

iopl(2), mem(4), <http://et.redhat.com/~rjones/ioport>, <http://www.faqs.org/docs/Linux-mini/IO-…>.

Authors

Richard W.M. Jones <rjones @ redhat . com>

Referenced By

inl(1), inw(1), outb(1), outl(1) and outw(1) are aliases of inb(1).

2009-03-09 ioport-1.2 I/O Ports