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====== DosPortAccess ======

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

===== Syntax =====

<code c>
DosPortAccess (Reserved, TypeOfAccess, FirstPort, LastPort)
</code>

===== Parameters =====

  * 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.

===== Return Code =====

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

  *0 NO_ERROR
  *5 ERROR_ACCESS_DENIED

===== Remarks =====

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.

===== Bindings =====

==== C ====

<code c>
#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 */
</code>

==== MASM ====


<code asm>
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
</code>

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