PDRIVER_IO_PORT_UCHAR_STRING callback function (video.h)

Article
04/01/2021

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

Syntax

PDRIVER_IO_PORT_UCHAR_STRING PdriverIoPortUcharString;

VP_STATUS PdriverIoPortUcharString(
  ULONG_PTR Context,
  ULONG Port,
  UCHAR AccessMode,
  PUCHAR Data,
  ULONG DataLength
)
{...}

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.

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 UCHAR string to be transferred. One character at a time is hooked out until the whole string is transferred.

DataLength

Specifies the number of UCHAR values in the string.

Return value

SvgaHwIoPortUcharString returns the final status of the operation.

Remarks

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

SvgaHwIoPortUcharString intercepts any byte access attempted by a full-screen MS-DOS application issuing either or both of the instructions REP OUTSB DX, ESI and REP INSB EDI, DX.

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

If one or more application-issued x86 INSB or OUTSB 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.

SvgaHwIoPortUcharString 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, SvgaHwIoPortUcharString must discard the buffered instructions. Otherwise, it should output them, a UCHAR at a time, to the specified, mapped I/O port.

SvgaHwIoPortUcharString should be made pageable.

Requirements

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