PDRIVER_IO_PORT_USHORT callback function (video.h)

Article
04/01/2021

SvgaHwIoPortUshort traps an I/O port range to which a full-screen MS-DOS application in an x86-based machine is sending a sequence of USHORT-sized data.

Syntax

PDRIVER_IO_PORT_USHORT PdriverIoPortUshort;

VP_STATUS PdriverIoPortUshort(
  ULONG_PTR Context,
  ULONG Port,
  UCHAR AccessMode,
  PUSHORT Data
)
{...}

Parameters

Context

Specifies the miniport driver-determined context value that was set in the EmulatorAccessEntriesContext member of VIDEO_PORT_CONFIG_INFO.

Port

Specifies the mapped I/O port to be trapped.

AccessMode

Specifies the type of access allowed, which can be one or a combination (ORed) of the following values:

EMULATOR_READ_ACCESS
EMULATOR_WRITE_ACCESS

Data

Pointer to the USHORT data to be transferred.

Return value

SvgaHwIoPortUshort returns the final status of the operation.

Remarks

Only miniport drivers of VGA-compatible SVGA adapters have SvgaHwIoPortXxx functions. (See SVGA Functions.)

SvgaHwIoPortUshort intercepts any range access attempted by a full-screen MS-DOS application issuing either or both of the instructions OUT DX, AX and IN AX, DX.

If the miniport driver enables the Port range for direct access by calling VideoSetTrappedEmulatorPorts, its SvgaHwIoPortUshort function will not be called. Such an application then will have direct access to the I/O port range, unless the miniport driver disables the Port range with another call to VideoSetTrappedEmulatorPorts.

If one or more application-issued x86 IN or OUT instructions might affect the state of the VGA-compatible adapter sequencer register, miscellaneous output register, or any adapter-specific register and, thereby, cause the machine to hang, the miniport driver must not enable the port for direct access by calling VideoPortSetTrappedEmulatorPorts.

SvgaHwIoPortUshort must buffer subsequent instructions from the application and check that none can hang the machine. If the application issues any sequence of instructions that might hang the machine, SvgaHwIoPortUshort must discard the buffered instructions. Otherwise, it should output them, a USHORT at a time, to the specified, mapped I/O port.

SvgaHwIoPortUshort should be made pageable.

Requirements

Requirement	Value
Target Platform	Desktop
Header	video.h (include Video.h)