SvgaHwIoPortUcharString

SvgaHwIoPortUcharString

VP_STATUS SvgaHwIoPortUcharString(

ULONG Context,
ULONG Port,
UCHAR AccessMode,
PUCHAR Data,
ULONG DataLength
);

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. Only miniport drivers of VGA-compatible SVGA adapters have SvgaHwIoPortXxx functions.

Parameters

Context

Specifies the miniport-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

Points 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.

Comments

SvgaHwIoPortUcharString will intercept 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 an application-issued x86 INSB or OUTSB instruction(s) 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.