DosPortAccess

This call requests or releases access to ports for I/O privilege.

DosPortAccess (Reserved, TypeOfAccess, FirstPort, LastPort)

• Reserved (USHORT) - input : Must be set to zero.
• TypeOfAccess (USHORT) - input : A request for or release of access to a port.
  • 0 - Request access
  • 1 - Release access.
• FirstPort (USHORT) - input : Starting (low) number in a contiguous range or a single port.
• LastPort (USHORT) - input : Ending (high) number in a contiguous range or a single port. If only one port is being used, FirstPort and LastPort should both be set to this port.

rc (USHORT) - return:Return code descriptions are:

• 0 NO_ERROR
• 5 ERROR_ACCESS_DENIED

Note that CLI/STI privilege is also granted automatically. There is no need to make an additional call to DosCLIAccess.

Applications that perform I/O to port(s) in IOPL segments must request port access from the operating system.

An application with no IOPL segments that accesses a device through a device driver or by an interface package such as VIO, does not need to issue this call. The device driver or interface package is responsible for obtaining the necessary I/O access.

#define INCL_DOSDEVICES
 
USHORT  rc = DosPortAccess(Reserved, TypeOfAccess, FirstPort, LastPort);
 
USHORT  0;             /* 0 */
USHORT  TypeOfAccess;  /* Request or release */
USHORT  FirstPort;     /* First port number */
USHORT  LastPort;      /* Last port number */
 
USHORT  rc;            /* return code */

EXTRN  DosPortAccess:FAR
INCL_DOSDEVICES     EQU 1
 
PUSH   WORD    0             ;Reserved (must be zero)
PUSH   WORD    TypeOfAccess  ;Request or release
PUSH   WORD    FirstPort     ;First port number
PUSH   WORD    LastPort      ;Last port number
CALL   DosPortAccess
 
Returns WORD