outp()

write one byte to a 80x86 hardware port

Synopsis:

#include <conio.h>
unsigned int outp( int port, int value );

Description:

The outp() function writes one byte, determined by value, to the 80x86 hardware port whose number is given by port.

A hardware port is used to communicate with a device. One, two or four bytes can be read and/or written from each port, depending on the hardware. Consult the technical documentation for your computer to determine the port numbers for a device and the expected usage of each port for a device.

Returns:

The value transmitted.

Examples:

#include <conio.h>

void main()
  {
    /* turn off speaker */
    outp( 0x61, inp( 0x61 ) & 0xFC );
  }

Classification:

Intel

Caveats:

When you use the outp() function, your program must be linked for privity level 1, and the process must be run by the superuser (root) or by a setuid program owned by the superuser. For more information on privity, see

• the cc -T option
• the Linker PRIVILEGE option.

See also:

inp(), inpd(), inpw(), outpd(), outpw()