EMULATOR_ACCESS_ENTRY structure (miniport.h)

The EMULATOR_ACCESS_ENTRY structure specifies an element in the EmulatorAccessEntries array set up in the VIDEO_PORT_CONFIG_INFO structure by drivers of VGA-compatible (SVGA) adapters on x86-based NT-based operating system platforms.

Syntax

typedef struct _EMULATOR_ACCESS_ENTRY {
  ULONG                     BasePort;
  ULONG                     NumConsecutivePorts;
  EMULATOR_PORT_ACCESS_TYPE AccessType;
  UCHAR                     AccessMode;
  UCHAR                     StringSupport;
  PVOID                     Routine;
} EMULATOR_ACCESS_ENTRY, *PEMULATOR_ACCESS_ENTRY;

Members

BasePort

Specifies the bus-relative physical address of the I/O port or ports to be hooked out by the V86 emulator. This value and the range of ports must fall within an access range of I/O ports already claimed in the registry by VideoPortGetAccessRanges or VideoPortVerifyAccessRanges.

NumConsecutivePorts

Specifies the number of consecutive ports to be hooked by the V86 emulator, starting at BasePort. This value is determined by the width of each hooked I/O port. For example, if port addresses 0x3C0 and 0x3C1 are hooked as a single USHORT-addressable port, this value should be 1.

AccessType

Specifies the size of the data transferred through the given I/O port as one of Uchar, Ulong, or Ushort.

AccessMode

Specifies how the given I/O port can be accessed as one or a combination (ORed) of the following values:

• EMULATOR_READ_ACCESS

• EMULATOR_WRITE_ACCESS

The I/O port range must be accessible in at least one of the preceding modes.

StringSupport

Indicates whether the driver-supplied SvgaHwIoPortXxx function supports string accesses in cases where many values of the given AccessType are "pumped" through an I/O port consecutively. If this member is set to TRUE, the Routine member must specify the entry point of a miniport driver-supplied SvgaHwIoPortXxxString function.

Routine

Pointer to the miniport driver's SvgaHwIoPortXxx that handles accesses to the port or ports described in this structure.

Remarks

VGA-compatible miniport drivers of SVGA video hardware in x86-based machines must define emulator access ranges, which a VGA-compatible miniport driver can set up with VideoPortSetTrappedEmulatorPorts to be accessed directly from full-screen MS-DOS applications for faster I/O. Such a driver must supply a set of SvgaHwIoPortXxx functions to validate any sequence of application-issued INs, INSB/INSW/INSDs, OUTs, and/or OUTSB/OUTSW/OUTSDs to each such I/O port range.

Data in each EMULATOR_ACCESS_ENTRY-type element is used to determine which I/O ports (memory locations at which adapter registers are accessible) in the miniport driver's access ranges have been taken over (hooked out) by the V86 emulator on x86-based platforms. Values written to these locations by full-screen MS-DOS applications are trapped and forwarded to the miniport driver's corresponding SvgaHwIoPortXxx function for validation before they are written to or read from the video adapter. However, the miniport driver can enable the application to directly access particular I/O port ranges by calling VideoPortSetTrappedEmulatorPorts to improve performance.

Requirements

Requirement	Value
Header	miniport.h (include Miniport.h)

See also

VIDEO_PORT_CONFIG_INFO

VideoPortVerifyAccessRanges

VideoPortSetTrappedEmulatorPorts

VIDEO_ACCESS_RANGE

VideoPortGetAccessRanges