DosPortAccess

Bindings:  C, MASM 

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. 

    Value     Definition 
    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 
 
 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.