DDDR/2 - Physical Video Device Drivers

Video devices are accessed by using Base Video Handlers (BVHs). These BVHs consist of one or more Dynamic Link Libraries (DLLs). In the representative case of the VGA, BVHVGA.DLL manages the device for full-screen sessions, while DISPLAY.DLL (renamed from IBMVGA.DLL) manages the device for the Presentation Manager interface. Although these device handlers are initialized by different sections of the system at this time, they are architecturally compatible and can easily be combined at a later date.

Video Device Handler Identification
The list of the active video device handlers and their components resides in the CONFIG.SYS file as environment variables. To conserve environment space, these variables are removed from the environment during Shell Initialization. The VIDEO_DEVICES environment variable lists the names of the environment variables that describe each of the video device handlers. Commas are used to separate the names in this list. The following is an example of how to specify the environment variables ARTICHOKE and WATERMELON as those defining the active video device handlers, with ARTICHOKE used as configuration number one, and WATERMELON used as configuration number two. SET VIDEO_DEVICES=ARTICHOKE,WATERMELON

The value of each environment variable that describes a video device handler is composed of three keywords and the values associated with them. These keywords are separated by blanks and can be specified in any order and in any combination of upper and lower case characters. The DEVICE keyword defines the list of names of the dynamic link libraries and physical device drivers which are combined to create the video device handler. The names are separated by commas, and their order determines the order in which the components will be initialized. These names represent only those parts of the BVH that need to be called to initialize the Call Vector Table. That is, physical device drivers should not be included in the list if they are only called by the dynamic link libraries and do not directly modify the Call Vector Table.

The default initialization entry point name for the dynamic link libraries is DEVENABLE. An alternate entry point name can be specified by following any DLL name with +AltName, where AltName is the entry point name.

The default initialization IOCtl for physical device drivers is Function 73h. An alternate function number and category can be specified by following the device name by +Func+Cat, where "Func" is the function number and "Cat" is the category. Both numbers must be specified in hexadecimal form. For details, see Function 73h under "Physical Device Driver Initialization" later in this chapter.

The following is an example of a device handler that is composed of two physical device drivers, DEV1 and DEV2, and three dynamic link libraries, DYN1 through DYN3. The second physical device driver uses an alternate initialization IOCtl and the third dynamic link library uses an alternate initialization entry point. POINTER$ is the default physical pointer device driver. SET ARTICHOKE=DEVICE(DEV1,DYN1,DEV2+74+05,DYN2,DYN3+OTHERENT)

DosOpen is called for each name in the list to check if it is a device driver with an associated "DEVICE=" statement in the CONFIG.SYS file. If the call fails, DosLoadModule is called to check if it is a dynamic link library. If both of these calls fail for any name in the list, the entire device is ignored.

If the optional PTRDEVP keyword is specified, it defines the names of the physical pointer device drivers. If it is not specified, it defaults to PTRDEVP(POINTER$). The following is an example of a device with only one dynamic link library component and a unique physical pointer device driver for protect mode. SET WATERMELON=DEVICE(SEEDLESS) PTRDEVP(PPOINT)

Note: This design is not limited strictly to physical video devices. By writing a device handler, video data could be written to any device, such as a printer or a plotter. In addition, by using alternate initialization entry points, multiple devices can be handled by the same physical device handler.

All of the video device handlers shipped with OS/2 2.1 are dynamic link libraries. They can be defined by the following environment variables, which use the default keywords of PTRDEVP(POINTER$) and PTRDEVR(POINTER$). SET VIO_IBMMPA=DEVICE(BVHMPA) SET VIO_IBMCGA=DEVICE(BVHCGA) SET VIO_IBMEGA=DEVICE(BVHEGA) SET VIO_IBMVGA=DEVICE(BVHVGA) SET VIO_IBM8514A=DEVICE(BVHVGA,BVH8514A) SET VIO_IBM8514A=DEVICE(BVH8514A) SET VIO_IBMXGA=DEVICE(BVHXGA)

The following statements define a system with an 8514 display attached to an 8514/A as the only active video device: SET VIDEO_DEVICES=VIO_IBM8514A SET VIO_IBM8514A=DEVICE(BVHVGA,BVH8514A)

However, the statement below defines a system with an 8514 display attached to an 8514/A, and another PS/2* display attached to the VGA connector, as independent video devices. SET VIDEO_DEVICES=VIO_IBMVGA,VIO_IBM8514A SET VIO_IBMVGA=DEVICE(BVHVGA) SET VIO_IBM8514A=DEVICE(BVH8514A)

Two other device handlers are provided with OS/2. The names of these device drivers are fixed. The Base Video Subsystem loads them automatically as they are needed.

BVHINIT.DLL is the generic device handler used by system installation and system initialization. It provides the minimum function necessary to support installation of the system and reporting of system errors during startup. It is loaded only if no other BVHs are successfully loaded.

BVHWNDW.DLL is the device handler that can support VIO window sessions and that provides the interface to the Presentation Manager interface by treating the PM interface as a virtual video device driver. BVHWNDW.DLL is loaded only for VIO window sessions.

Video Device Chaining
Video device handlers (BVHs) can be chained together when multiple BVHs share the responsibility of supporting a specific video adapter. This is accomplished by allowing previously loaded BVHs to attempt the handling of BVH functions. BVH8514A and BVHXGA are chained BVHs shipped with the product that provides this support.

A VGA and 8514A Scenario
During system initialization, BVHVGA is first called to initialize the Call Vector Table, that is, the table used by BVS to give control to the BVH routines. BVHVGA functions as though no other BVH will be handling the device. Next, BVH8514A is called to initialize the same Call Vector Table. However, BVH8514A saves a copy of the Call Vector Table before changing it.

When calls are made to this chained BVH, BVH8514A receives the call and passes it to the BVHVGA routine through the saved Call Vector Table. If an error occurs or if the results of the routine need to be modified, BVH8514A handles the call. Thus, BVH8514A uses the BVHVGA routines to perform all common functions. Device chaining can be viewed as a mechanism to allow one BVH to filter function calls to another BVH.

Primary Display Identification
The primary display is the default display chosen by VIO for full-screen sessions. It is also the display on which VIO and hard error pop-ups are shown. Notice that the primary display used by VIO is not necessarily the display on which the Presentation Manager environment runs. The Presentation Manager interface normally runs on the highest resolution display. In a dual-display configuration, the highest resolution display is not necessarily a display that can be used in text mode.

The primary display is the pop-up display. A physical video device driver must determine if it represents the pop-up display. If so, the video device driver must specify that it represents the pop-up display configuration in Query Config Info.

WrtToScrn/Panic Write Support
Before the video subsystem is loaded, and when the system is about to abnormally terminate, messages are sent to the screen by the WrtToScrn function, also known as Panic Write. This function switches to real mode and executes the INT 10h function to set the video mode to a text mode ( BIOS mode 3). It then uses BIOS INT 10h, "Write TTY", to display the message.

However, adapters such as the 8514/A have native modes that cannot be changed by INT 10h. In such cases, the BVH must include a Level 0 device driver that hooks INT 10h to provide extended set mode support. This hook must force the adapter out of its native mode, and then pass control to the previous INT 10h support. If these conditions are not satisfied, the adapter should not drive the power up display.

System Installation
The generic device handler, BVHINIT.DLL, is used primarily by system installation. It is also used for those situations when video devices have not been identified in the CONFIG.SYS file. It provides only the functions required for system installation and is otherwise device-independent.

Through VioGetConfig BVHINIT.DLL reports the highest function video adapter and display it can identify. It can identify only the MPA, CGA, EGA, VGA, 8514A, and XGA, along with their respective displays. Although it does not support mode and font setting, it attempts to load the 850 code page for the current EGA or VGA mode during system initialization.

If video devices have not been identified in the CONFIG.SYS file, the generic device handler attempts to load each of the following devices, until one is successfully loaded: GENERIC=DEVICE(BVHVGA,BVH8514A) GENERIC=DEVICE(BVHVGA) GENERIC=DEVICE(BVHEGA) GENERIC=DEVICE(BVHCGA) GENERIC=DEVICE(BVHINIT)

Loadable Device Drivers
Loadable device drivers present a unique problem when used to support video devices because some video support can be required before the DEVICE= statements have been processed by system initialization. To handle this problem, two different initialization calls are made.

The Enable subfunction determines which type of initialization is to be done. If the subfunction is 1 (Fill Logical Device Block), the DevEnable function is requested to add all of the functions supported by the device handler to the Call Vector Table. If the subfunction is 3 (Fill Initialization Device Block), the InitEnable function is requested to add only those functions, that can be supported without the use of a loadable device driver to the Call Vector Table.

Regardless of the success of the InitEnable function, the DevEnable function is called at Shell Initialization time. See DevEnable, and InitEnable for more information.

Video Device Handler Interfaces
The functions that follow are video primitives reserved for use by OS/2 system components. Unexpected results can occur if these functions are started by applications. All of the video device handler functions described below (except for the DLL Initialization function) use the same calling sequence. Parameters are passed to the routines on the stack. The entry point is found in the BVH Call Vector Table at the index of the function number. The calling sequence used to invoke all the routines is as follows: PUSH@   OTHER    Environment        ; Environment buffer PUSH@   OTHER    ParmBlock          ; Parameter block PUSH    DWORD    Function           ; Function number

CALL    FAR      BVH Routine Entry Point Environment:

The environment buffer. The format of this buffer is defined by the BVH developer. The selector is a huge selector.

ParmBlock:

A data structure containing all of the parameters of the operation to be performed. The general format of this structure is: Length of parameter block in bytes (=NN) WORD Flags                                    WORD

Bit 0 indicates whether the physical hardware is updated.

OFF = Initialize only the environment buffer ON = Initialize the environment buffer and the hardware state

Bits 1 through 15 are reserved and must be OFF. The length of the parameter block is the total length, including the length field itself. The number in parentheses (=NN) represents the value of this field, if it is a constant. The first flag bit always indicates a background versus foreground state for this function. If the bit is ON, the adapter is actually updated, as it is when an application is in the foreground. If the bit is OFF, only the buffer that is used to shadow the adapter when an application is in the background is actually updated. All bits that are not currently defined as reserved must be OFF.

Function:

The function identifier for this routine. This corresponds to the offset into the Call Vector Table, and can be used to determine the number of parameters on the stack. This is consistent with the existing DDI used by the Presentation Manager interface. All routines are expected to return with AX = 0 if no error was detected. Otherwise, an error code is returned in AX. The following errors are common to all commands:

ERROR_VIO_INVALID_LENGTH, if the parameter block length is incorrect. ERROR_VIO_INVALID_PARMS, if a reserved flag bit is non-zero, or if                              the function number does not match the routine.

DevEnable
This function fills the entries in the Call Vector Table for all of the functions supported by this BVH. It is called as a subfunction of the Presentation Manager enable function entry point. To initialize the Call Vector Table for dynamic link libraries: PUSH DWORD   Parameter2    ; Variable parameter 2 PUSH DWORD   Parameter1    ; Variable parameter 1 PUSH DWORD   Subfunction   ; Enable subfunction

CALL FAR     DevEnable

Parameters
Parameter2 for Subfunction=1

A far pointer to this structure: DWORD  Flags Pointer DWORD  Call Vector Table Flags Pointer

Pointer to where the flags that control calls to the Fill Physical Device Block function go.

Call Vector Table

Pointer to the default dispatch table containing the addresses of the default handler functions and the functions supported by this component. Each entry in the Call Vector Table is the far address of a Video Device Handler function, which must be callable from both Ring 2 and Ring 3. The far address of the nth BVH function is the nth DWORD in the table, beginning with Function 0.

The functions listed below are defined as follows: Parameter1 for Subfunction=1

Far pointer to this structure: DWORD  Engine Version DWORD  Count of Table Functions Engine Version

Version of the Presentation Manager Graphics Engine.

Count of Table Functions

The number of entries in the passed dispatch table. The driver can write only this many entries into the table.

Subfunction

The Presentation Manager enable subfunction number. Its value must be 1 to start the Presentation Manager Fill Logical Device Block subfunction. All pieces of the BVH must support this function. Pieces of the BVH that do not support the Presentation Manager interface do not need to support the other functions. Any function not supported will return PMERR_DEV_FUNC_NOT_INSTALLED.

Remarks

This function is supported by the video dynamic link functions and is called only once for each adapter supported by the physical device driver. A video device handler determines if the display adapter and that which the adapter supports is present. If not present, this function returns an error. Every part of a BVH must successfully initialize the Call Vector Table for that device to be usable by the OS/2 operating system.

InitEnable
This function fills the entries in the Call Vector Table for all of the functions supported by this BVH using only SCREEN$ device driver. It is called with parameters similar to the DevEnable entry point specified in DevEnable, except for the Subfunction parameter.

To initialize the Call Vector Table for dynamic link libraries: PUSH DWORD   Parameter2    ; Variable parameter 2 PUSH DWORD   Parameter1    ; Variable parameter 1 PUSH DWORD   Subfunction   ; Enable subfunction CALL FAR     InitEnable

Parameters
Parameter2 for Subfunction=3

See DevEnable.

Parameter1 for Subfunction=

See DevEnable. Subfunction is the Presentation Manager enable subfunction number. Its value must be 3 to start the Presentation Manager Fill Initialization Device Block subfunction. The default entry point of DevEnable can be overridden by specifying an alternate name in the DEVICE parameter describing this BVH in the CONFIG.SYS file.

Remarks

This function is called only if video functions are required before Shell Initialization.

The BVH must be able to support the following subfunctions: See DevEnable.

Function 100h

 * Text Buffer Update - Function 100h:This function performs text updates to the logical and physical video buffers. All references to the buffer are made through the text row and column of each cell affected by the called function.
 * Parmlength:Length of the data structure in bytes (greater than, or equal to, 26), including the Lengthfield itself. The maximum length is 44 bytes. Values not passed are assumed to be the default values for the environment.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical video buffer needs to be updated.
 * OFF = The physical video buffer must not be updated.
 * ON = The physical video buffer must be updated.
 * Bit 1 indicates whether the logical video buffer needs to be updated.
 * OFF = The logical video buffer may optionally be updated.
 * ON = The logical video buffer must be updated.
 * Bit 2 indicates that attribute information in the user buffer is in CGA format and might need to be translated into the format used by the device. This bit is set for VioWrtTTY calls any time that ANSI is active, because

ANSI recognizes only CGA format attributes.
 * OFF = Use attributes in existing format.
 * ON = Translation to or from CGA format required.
 * Bits 3-15 are reserved and must be OFF.


 * Selector/Offset of the Application Data Area :Pointer to the application's data area, which provides either the source or the destination for the buffer operation.
 * Selector/Offset of the Secondary Data Area: Pointer to the additional parameter required by this type of update operation. It is used to define, at most, one cell of information that is used repetitively as filler. This is used only with Index = 3, 4, 5, 6, or 9.
 * Index :Defined as follows:
 * 0 = Read Cell Types from (Row,Col) as word of flags:
 * Bit 0 indicates whether the cell is part of a single or double cell character.
 * OFF = The cell represents a single cell character.
 * ON = The cell represents part of a double cell character.  Bit 1 is examined for more information.
 * Bit 1 indicates whether the cell is a trailing cell of a double cell character.
 * OFF = The cell represents the leading or only cell of a character.
 * ON = The cell represents the trailing cell of a double cell character.
 * Bits 2 thru 15 are reserved and must be OFF.
 * 1 = Read Characters from (Row,Col)
 * 2 = Read Cells from (Row,Col)
 * 3 = Scroll (Row,Col) through (Row2,Col2) Up
 * 4 = Scroll (Row,Col) through (Row2,Col2) Down
 * 5 = Scroll (Row,Col) through (Row2,Col2) Left
 * 6 = Scroll (Row,Col) through (Row2,Col2) Right
 * 7 = Write Cells to (Row,Col)
 * 8 = Write Characters to (Row,Col)
 * 9 = Write Characters with Constant Attr to (Row,Col)
 * 10 = Write Repeated Character to (Row,Col)
 * 11 = Write Repeated Attribute to (Row,Col)
 * 12 = Write Repeated Cell to (Row,Col)
 * 13 = Copy LVB Rect to PVB


 * Starting Row:Defines the text location (row) in the Video Buffer at which the update is to be started. For Function 13, this is the upper-left corner of the rectangle to be written.
 * Starting Column :Defines the text location (column) in the Video Buffer at which the update is to be started. For Function 13, this is the upper-left corner of the rectangle to be written.
 * Secondary Row :Defines the text location (row) in the Video Buffer to which cells will be moved. This is used only when moving cells from one location to another (Index=3-6). For Function 13, this is the lower-right corner of the rectangle to be written.
 * Secondary Column :Defines the text location (column) in the Video Buffer to which cells will be moved. This is used only when moving cells from one location to another (Index=3-6). For Function 13, this is the lower-right corner of the rectangle to be written.
 * Repeat Factor:Repeat factor used when updating the buffer. It represents the number of character cells to be updated, or the number of rows or columns to be scrolled. This is used for both input and output.
 * Logical Buffer Selector :Selector used for the beginning of the logical video buffer. This selector is a huge selector with a maximum size of 1MB.
 * TouchXLeft :The X-coordinate of the upper-left corner of the tightest rectangle that circumscribes the cells touched by the current function. If no cells were touched (as in a Read), -1 is returned. Collectively, this field and the next three fields form an area of influence for the call. This field is returned by the BVH.
 * TouchYTop :The Y-coordinate of the upper-left corner of the tightest rectangle that circumscribes the cells touched by the current function. If no cells were touched, -1 is returned. This field is returned by the BVH.
 * TouchXRight :The X-coordinate of the lower-right corner of the tightest rectangle that circumscribes the cells touched by the current function. If no cells were touched, -1 is returned. This field is returned by the BVH.
 * TouchYBottom :The Y-coordinate of the lower-right corner of the tightest rectangle that circumscribes the cells touched by the current function. If no cells were touched, -1 is returned. This field is returned by the BVH.
 * LVBRowOff :The row offset of the upper-left corner of the LVB in PVB coordinates. All reads, writes, and scrolls are done in PVB coordinates.
 * LVBColOff :The column offset of the upper-left corner of the LVB in PVB coordinates. All reads, writes, and scrolls are done in PVB coordinates.
 * LVBWidth :The width of the LVB in cells. Must be greater than 0.
 * LVBHeight :The height of the LVB in cells. Must be greater than 0.
 * LVBFormatID :The format ID of the LVB. If this value and attribute count are both 0, the Format ID and attribute count for the current mode are used.
 * LVBAttrCount :The attribute count for the LVB.

The Text Buffer Update routine returns with AX = 0, if no error was detected. Otherwise, the following error codes are returned in AX: The Touchxxxx fields circumscribe the area of the LVB, or PVB, for a rectangle that was potentially changed by the given operation. For example, a Write that included the cells (10,12) to (79,12), (0,13) to (79,13), and (0,14) to (8,14) returns TouchXLeft=0, TouchYTop=12, TouchXRight=79, and TouchYBottom=14. Any new functions added to the BVH interface that can affect the data in the PVB or LVB must include a return area for the rectangle of the video buffer that was affected by the given call.
 * Returns
 * Remarks

The LVBxxxx fields indicate that an LVB can differ from the normal LVB format. The information about the LVB is taken from these fields, if they are included. Notice that these fields allow an LVB to begin at a location other than (0,0) and allow LVBs of different row and column dimensions.

Function 101h
This function causes the Environment Buffer and the video adapter (optional) to be initialized.
 * Initialize Environment - Function 101h


 * Parmlength :Length of parameter block in bytes (=6) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is updated.
 * OFF = Initialize only the environment buffer.
 * ON = Initialize the environment buffer and the hardware state.
 * Bit 1 indicates whether the 3xBox is being initialized.
 * OFF = The 3xBox is not being initialized.
 * ON = The 3xBox is being initialized.
 * Bits 2 thru 15 are reserved and must be OFF.


 * Logical Buffer Selector :Selector used for the beginning of the logical video buffer. This selector is a huge selector with a maximum size of 1MB.

This routine always returns with AX = 0. It must be possible to call Restore Environment before Save Environment.
 * Parameter Packet Format
 * Returns
 * Remarks

Function 102h
This function is used to save all aspects of the video adapter, including the hardware state and the video buffers.
 * Save Environment - Function 102h


 * Parmlength :Length of parameter block in bytes (=6) passed on input.
 * Flags :Defined as follows:
 * Bit 0 is reserved and must be Off.
 * Bit 1 indicates whether hardware state (mode, CLUT, everything except the buffer) is saved.
 * OFF = The hardware state is not saved.
 * ON = The hardware state is saved.
 * Bit 2 indicates whether the physical display is fully saved for session switching.
 * OFF = The physical display is not fully saved.
 * ON = The physical display is fully saved.
 * Bit 3 indicates whether the physical display is partially saved for pop-ups.
 * OFF = The physical display is not partially saved.
 * ON = The physical display is partially saved.
 * Bits 4 thru 15 are reserved and must be OFF.


 * Logical Buffer Selector :Selector used for the beginning of the logical video buffer. This selector is a huge selector with a maximum size of 1MB.

The Save Environment routine returns with AX=0 if it can successfully save the environment to the Environment Block and the Logical Video Buffer. Otherwise, it returns with AX=ERROR_VIO_MODE.
 * Parameter Packet Format
 * Returns

Bits 2 and 3 are mutually exclusive. If both are specified, bit 3 will be ignored. Bit 4 is used in combination with bits 2 and 3. The code and data segments referenced or accessed to perform the functions selected by bits 1 and 3 must be locked during device driver initialization. The format of the data saved in the segments passed as input is determined by the device handler.
 * Remarks

Partial saves are started on VIO and hard error pop-ups. Pop-ups appear on the primary display configuration. The device driver must save whatever portion of the physical display buffer that is overlaid by the pop-up. To display a pop-up, OS/2 2.1 switches to the highest resolution 80 x 25 text mode supported by the primary display configuration (mode 3 or 7, whichever is listed first in the list of modes supported by the display configuration). Alternatively, if a device driver's physical display buffer is not overlaid by a pop-up, the physical device driver returns zero for partial save size.

When a hard error pop-up occurs before a VIO pop-up has cleared, the Save Environment function is called twice before the Restore Environment is called. Therefore, the device handler must be prepared to handle both a partial save of a graphics mode and a full save of the text mode of the user pop-up.

OS/2 allocates the buffer in which the physical display buffer is saved by using DosAllocHuge. The selector to the Data Packet addresses the first of n segments in which the physical display buffer is saved. (The offset to the Data Packet should be ignored.) The selector to the second segment can be calculated by adding the DosAllocHuge increment to the first selector value. The third selector can similarly be calculated by adding the DosAllocHuge increment to the second selector value, and so forth. Enough selectors are allocated to meet the full/partial buffer requirement specified by the physical device driver. The selectors each address 64KB except the last selector, which addresses the remainder.

Function 103h
This function is used to restore all aspects of the video adapter, including the hardware state and the video buffers.
 * Restore Environment - Function 103h
 * Parmlength :Length of parameter block in bytes (=6) passed on input.
 * Flags :Defined as follows:
 * Bit 0 is reserved and must be Off.
 * Bit 1 indicates whether hardware state (mode, CLUT, everything except the buffer) is saved.
 * OFF = The hardware state is not restored.
 * ON = The hardware state is restored.
 * Bit 2 indicates whether the physical display is fully restored for session switching.
 * OFF = The physical display is not fully restored.
 * ON = The physical display is fully restored.
 * Bit 3 indicates whether the physical display is partially restored for pop-ups.
 * OFF = The physical display is not partially restored.
 * ON = The physical display is partially restored.
 * Bits 4 thru 15 are reserved and must be OFF.

The Restore Environment routine returns with AX = 0 if it can successfully restore the environment to the Environment Block and the Logical Video Buffer. Otherwise, it returns with AX = ERROR_VIO_MODE. See Function 102h for more information.
 * Logical Buffer Selector :Selector used for the beginning of the logical video buffer. This selector is a huge selector with a maximum size of 1MB.
 * Returns

Function 104h
This function returns all of the information necessary to identify the current video adapter and display. This function returns with AX = ERROR_VIO_INVALID_LENGTH only if the Length specified is less than 2.
 * Query Config Info - Function 104h
 * Parmlength :Length of parameter block in bytes (=8) passed on input.
 * Flags :Must be zero.
 * Parameter Packet Format
 * Returns

The Environment Buffer is not used by this function. The Environment Buffer address is passed as a DWORD of zero. If the Length specified in the Config Data is larger than the maximum possible length, or if the Length is specified as 2 (the length of Length field itself), it is replaced by the largest valid length.
 * Remarks

Function 105h
This function returns various forms of DBCS information used by the display. This function is used to get the DBCS display information associated with the given environment buffer, and returns with AX = ERROR_VIO_INVALID_ LENGTH if the Length specified is less than 2 or the buffer was too short to return all of the DBCS display information. Otherwise, Query DBCS Display Info returns with AX = 0.
 * DBCS Display Info - Function 105h
 * Parmlength :Length of parameter block in bytes. If Length is specified as 2, only the maximum length of the parameter block is returned in the length field. If the length is not 2, it defines the maximum amount of data returned.
 * Flags: Must be zero.
 * DBCS Table Length: Length of double cell character table.
 * DBCS Table Offset: Offset of double-cell character table, which consists of WORD pairs that define the low and high limits (inclusive) of ranges of double-cell characters.
 * Parameter Packet Format
 * Returns

Function 106h
This function reads the definitions of the colors from the Color Lookup Table.
 * Query Color Lookup Table - Function 106h
 * Parmlength :Length of parameter block in bytes (=12) passed on input.
 * Flags: Defined as follows:
 * Bit 0 indicates whether the physical hardware is to be read.
 * OFF = Return data from the environment buffer only.
 * ON = Read the hardware to update the environment buffer before returning the requested data.
 * Bits 1-15 are reserved and must be OFF.

This function returns with AX = 0 if it can successfully get all of the requested registers from the Color Lookup Table. Otherwise, this routine returns with AX = ERROR_VIO_INVALID_PARMS if an invalid color register was requested, or AX = ERROR_VIO_INVALID_LENGTH if too many registers were requested.
 * Color Lookup Table Far Address :Far address of Color Lookup Table. The Table format is device-dependent. Three-byte table entries are returned for the VGA. Each table entry contains a red, green, and blue color index, respectively.
 * Index :Index of the first table entry to get.
 * Table Entry Quantity :Number of table entries to get. Three-byte table entries are returned for the VGA. Each table entry contains a red, green, and blue color index, respectively.
 * Parameter Packet Format
 * Returns

Function 107h
This function loads the definitions of the colors from the Color Lookup Table.
 * Set Color Lookup Table - Function 107h
 * Parmlength :Length of parameter block in bytes (=12) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is updated.
 * OFF = Update only the environment buffer.
 * ON = Update the environment buffer and the hardware state.
 * Bits 1-15 are reserved and must be OFF.


 * Color Lookup Table Far Address :Far address of Color Lookup Table. The Table format is device-dependent. The VGA format has three bytes containing the red, green and blue indices, respectively, for each color being set.
 * Index :Index of the first table entry to set.
 * Table Entry Quantity :Number of table entries to set.


 * Parameter Packet Format

This function returns with AX = 0 if it can successfully set all of the registers in the Color Lookup Table. Otherwise, it returns with AX = ERROR_VIO_INVALID_PARMS if an invalid color register was requested, or AX = ERROR_VIO_INVALID_LENGTH if too many registers were requested.
 * Returns

Function 108h
This function returns all of the information related to the cursor.
 * Query Cursor Info - Function 108h
 * Parmlength :Length of parameter block in bytes (=16) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is to be read.
 * OFF = Return data from the environment buffer only.
 * ON = Read the hardware to update the environment buffer before returning the requested data.
 * The remaining flags select the information to be returned:
 * Bit 1 selects cursor position.
 * Bit 2 selects cursor type.
 * Bits 3-15 are reserved and must be Off.


 * Row :0 is the top row.
 * Column :0 is the left column.
 * Top Cursor Scan Line :If n scan lines, 0 is top scan line and n-1 is bottom scan line.
 * Bottom Cursor Scan Line :If n scan lines, 0 is top scan line and n-1 is bottom scan line.
 * Cursor Width :Cursor width in columns, if text mode; in pels, if graphics mode.
 * Cursor Attribute :Cursor attribute: -1 = hidden, if text mode; other values = color attribute, if graphics mode.


 * Parameter Packet Format

This function returns with AX = 0 if it can successfully get all of the cursor information requested. Otherwise, it returns with AX = ERROR_VIO_INVALID_PARMS.
 * Returns

Function 109h
This function sets all of the information related to the cursor.
 * Set Cursor Info - Function 109h
 * Parmlength: Length of parameter block in bytes (=16) passed on input.
 * Flags: Defined as follows:
 * Bit 0 indicates whether the physical hardware is updated.
 * OFF = Update only the environment buffer.
 * ON = Update the environment buffer and the hardware state.
 * The remaining flags select the options to be set:
 * Bit 1 selects cursor position.
 * Bit 2 selects cursor type.
 * Bits 3-15 are reserved and must be OFF.


 * Row :0 is the top row.
 * Column :0 is the left column.
 * Top Cursor Scan Line: If n scan lines, 0 is top scan line and n-1 is bottom scan line.
 * Bottom Cursor Scan Line: If n scan lines, 0 is top scan line and n-1 is bottom scan line.
 * Cursor Width: Cursor width in columns, if text mode; in pels, if graphics mode.
 * Cursor Attribute :Cursor attribute: -1 = hidden, if text mode; other values = color attribute, if graphics mode.


 * Parameter Packet Format

This function returns with AX = 0 if it can successfully set all of the cursor information requested. Otherwise, it returns with AX equal to:
 * Returns
 * ERROR_VIO_MODE if it cannot support the function in the current mode
 * ERROR_VIO_ROW if the row number is out of range
 * ERROR_VIO_COL if the column number is out of range

Function 10Ah
This function returns the current active font or a selected font for the current code page. The format of the font definition is determined by the type of adapter.
 * Query Font - Function 10Ah
 * Parmlength :Length of parameter block in bytes (=14) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is to be read.
 * OFF = Return data from the environment buffer only.
 * ON = Read the hardware to update the environment buffer before returning the requested data.
 * Bit 1 indicates whether a specific font is to be returned instead of the current font.
 * OFF = Return the current font.
 * ON = Return the selected font for the current code page.  Setting this flag indicates that the pel columns and rows are used as input to select the font.
 * Bits 2-15 are reserved and must be OFF.


 * Font Buffer Far Address: Data area in which the font definition is returned.
 * Data Area Length :Length of data area in which font table is returned.
 * Pel Columns :Pel columns.
 * Pel Rows: Pel rows.


 * Parameter Packet Format

If the Length is specified as 0, no font is returned. Instead, the Length field returns the size needed to hold the font. Query Font returns with AX = 0 if it can successfully read the font. Otherwise, it returns with AX = ERROR_VIO_INVALID_PARMS.
 * Returns

Function 10Bh
This function sends a user font definition to the device handler. If the font is appropriate for the current mode, it is loaded into the adapter. If not, it is saved for possible use on subsequent calls to SetMode. The format of the font definition is determined by the type of adapter.
 * Set Font - Function 10Bh
 * Parmlength
 * Length of parameter block in bytes (=14) passed on input.


 * Flags
 * Defined as follows:
 * Bit 0 indicates whether the physical hardware is updated.
 * OFF = Update only the environment buffer.
 * ON = Update the environment buffer and the hardware state.
 * Bits 1-15 are reserved and must be OFF.


 * Font Buffer Far Address :Far address of the font buffer containing the font set in compact form.
 * Data Area Length
 * Length of data area containing the font table to be set.


 * Pel Columns
 * Pel columns.


 * Pel Rows
 * Pel rows.


 * Parameter Packet Format

This function returns with AX = 0 if it can successfully load the font. Otherwise, it returns with AX = ERROR_VIO_INVALID_PARMS.
 * Returns

Function 10Ch
This function returns all of the information pertaining to the current video mode.
 * Query Mode - Function 10Ch
 * Parmlength: Length of parameter block in bytes (=8) passed on input.
 * Flags: Defined as follows:
 * Bit 0 indicates whether the physical hardware is to be read.
 * OFF = Return data from the environment buffer only.
 * ON = Read the hardware to update the environment buffer before returning the requested data.
 * Bits 1-15 are reserved and must be OFF.


 * Mode Data Structure Far Address: Far Address of the Mode data structure defined by VioGetMode.


 * Parameter Packet Format

If the Length specified in the Config Data is larger than the maximum possible length or if the Length is specified as 2, it is replaced by the largest valid length. This function returns with AX = ERROR_VIO_INVALID_LENGTH only if the Length specified is less than 2.
 * Returns

Function 10Dh
This function sets the video mode of the video adapter. For text modes, it considers not only what display characteristics it can support but also what ROM, code page, and user-defined fonts it has available.
 * Set Mode - Function 10Dh
 * Datalength :Length of the data structure in bytes, including Length itself (=8).
 * Flags: Defined as follows:
 * Bit 0 indicates whether the physical hardware is updated.
 * OFF = Update only the environment buffer.
 * ON = Update the environment buffer and the hardware state.
 * Bit 1 indicates whether the mode is changed or only validated.
 * OFF = Perform normal mode setting.
 * ON = Perform only mode validation.
 * Bits 2-15 are reserved and must be OFF.


 * Mode Data Structure Far Address :Far Address of the Mode data structure defined by VioSetMode.


 * Parameter Packet Format

Set Mode returns with AX = 0 if it can set the requested mode. Otherwise, it returns with AX = ERROR_VIO_MODE.
 * Returns

This function must validate the mode data without using the environment buffer, because it might not have been initialized or might not be valid for this device. This function implicitly initializes the environment buffer if it has not already been done.
 * Remarks

Function 10Eh
This function queries the relationship between the text attributes and the color registers.
 * Query Palette Registers - Function 10Eh
 * Datalength :Length of parameter block in bytes (=12) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is to be read.
 * OFF = Return data from the environment buffer only.
 * ON = Read the hardware to update the environment buffer before returning the requested data.
 * Bits 1-15 are reserved and must be OFF.


 * Palette Buffer Far Address :Data area where a 1-WORD entry for each register containing its color value is returned.
 * Palette Register Index: Index of first palette register to get.
 * Register Quantity: Number of registers to return.


 * Parameter Packet Format

This function returns with AX = 0 if it can successfully get all of the requested palette registers. Otherwise, it returns with AX = ERROR_VIO_ INVALID_PARMS if an invalid color register was requested, or AX = ERROR_VIO _INVALID_LENGTH if too many registers were requested.
 * Returns

Function 10Fh
This function defines the relationship between the text attributes and the color registers.
 * Set Palette Registers - Function 10Fh
 * Parmlength :Length of parameter block in bytes (=12) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is updated.
 * OFF = Update only the environment buffer.
 * ON = Update the environment buffer and the hardware state.
 * Bits 1-15 are reserved and must be OFF.


 * Palette Buffer Far Address : Far address of palette register buffer. Data area with 1 WORD, containing the color value for each register set.
 * Palette Register Index :Index of first palette register to set. Data area with 1 WORD, containing the color value for each register set.
 * Register Quantity :Number of registers to set.


 * Parameter Packet Format

This function returns with AX = 0 if it can successfully set all of the requested palette registers. Otherwise, it returns with AX = ERROR_VIO_ INVALID_PARMS if an invalid color register was requested, or AX = ERROR_VIO _INVALID_LENGTH if too many registers were requested.
 * Returns

Function 110h
This function returns an LDT selector that can be used to access the physical video buffer. The current physical video buffer is returned unless a specific address range is requested.
 * Query Physical Buffer - Function 110h
 * Parmlength :Length of parameter block in bytes (=12) passed on input.
 * Flags :Must be zero.
 * Query Physical Buffer Far Address :Far Address of the Query Physical Buffer data structure defined by VioGetPhysBuf.


 * Parameter Packet Format

Query Physical Buffer returns with AX = 0 if it can successfully allocate the LDT selector. Otherwise, it returns with AX set by the PhysToUVirtdevice helper function or with AX = ERROR_VIO_INVALID_PARMS if the requested buffer resides outside the valid range for the device.
 * Returns

If the physical display buffer address and length passed on input are 0, this subfunction returns an LDT selector, that corresponds to the current mode.
 * Remarks

A physical video device driver must provide Read/Write access to the physical address range where the physical display buffer is located. The physical device driver must provide Read-only access to the physical address range where the ROM fonts are located. If the physical address passed on input is not within the physical display buffer or ROM font ranges, an error is returned.

Function 111h
This function deallocates an LDT selector that was acquired by a call to the Query Physical Buffer routine.
 * Free Physical Buffer - Function 111h
 * Parmlength :Length of parameter block in bytes (=6) passed on input.
 * Flags :Must be zero.
 * LDT Selector :LDT Selector.


 * Parameter Packet Format

This function always returns with AX = 0.
 * Returns

Function 112h
This function reads various minor features of the video adapter, including the blink state, border color, underscore line, and scrollable rectangle of the screen.
 * Query Variable Info - Function 112h
 * Parmlength :Length of parameter block in bytes (=26) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is to be read.
 * OFF = Return data from the environment buffer only.
 * ON = Read the hardware to update the environment buffer before returning the requested data.
 * The remaining flags select the information to be returned:
 * Bit 1 selects blink versus background color.
 * Bit 2 selects overscan (border) color.
 * Bit 3 selects scan line for underscore.
 * Bit 4 selects video enable.
 * Bit 5 selects the display mask.
 * Bit 6 selects code page.
 * Bit 7 forces a code page set (used with 6).
 * Bit 8 gets the scrollable rectangle.
 * Bits 9-15 are reserved and must be OFF.


 * Blink/Background Intensity :Blink versus background intensity:
 * 0 = blink.
 * 1 = background intensity.

bit 0 = plane 0 ?        ?     ?         ?     ?         ?   bit 31 = plane 31
 * Overscan (border) Color :Overscan (border) Color.
 * Scan Line: Scan line for underscore (0-31); 32 = no underscore.
 * Video Enable :Video enable: 0 = OFF and 1 = ON. OFF means off until the physical device driver is told to turn it back on. If the video signal is turned off and then the mode is set, the signal must remain off.
 * Display Mask :Display mask:

bit state = 0, plane disabled for display. bit state = 1, plane enabled for display.

(Planes disabled for display result in 0 to palette.)
 * Code Page: Code Page.
 * Scrollable Rectangle - Left: The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Scrollable Rectangle - Top :The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Scrollable Rectangle - Right :The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Scrollable Rectangle - Bottom :The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Screen Rows :The number of text rows in the current mode.
 * Screen Columns :The number of text columns in the current mode.


 * Parameter Packet Format

Query Variable Info returns with AX = 0 if it can successfully get the selected variable information. Otherwise, it returns with AX = ERROR_VIO_ INVALID_PARMS.
 * Returns

Function 113h
This function sets the minor features of the video adapter, including the blink state, border color, underscore line, and scrollable rectangle of the screen.
 * Set Variable Info - Function 113h
 * Parmlength
 * Length of parameter block in bytes (=26) passed on input.


 * Flags
 * Defined as follows:
 * Bit 0 indicates whether the physical hardware is updated.
 * OFF = Update only the environment buffer.
 * ON = Update the environment buffer and the hardware state.
 * The remaining flags select the information to be set:
 * Bit 1 selects blink versus background color.
 * Bit 2 selects overscan (border) color.
 * Bit 3 selects scan line for underscore.
 * Bit 4 selects video enable.
 * Bit 5 selects the display mask.
 * Bit 6 selects code page.
 * Bit 7 forces a code page set (used with 6).
 * Bit 8 gets the scrollable rectangle.
 * Bits 9-15 are reserved and must be OFF.


 * Blink/Background Intensity :Blink versus background intensity:
 * 0 = blink.
 * 1 = background intensity.

bit 0 = plane 0 ?        ?     ?         ?     ?         ?   bit 31 = plane 31
 * Overscan (border) Color : Overscan (border) Color.
 * Scan Line :Scan line for underscore (0-31); 32 = no underscore.
 * Video Enable :Video enable: 0 = OFF and 1 = ON. OFF means off until the physical device driver is told to turn it back on. If the video signal is turned off and then the mode is set, the signal must remain off.
 * Display Mask :Display mask:

bit state = 0, plane disabled for display. bit state = 1, plane enabled for display.

(Planes disabled for display result in 0 to palette.)
 * Code Page :Code Page.
 * Scrollable Rectangle - Left:The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Scrollable Rectangle - Top:The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Scrollable Rectangle - Right:The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Scrollable Rectangle - Bottom:The scrollable rectangle fields indicate the area of the screen that can scroll during scroll and write TTY operations.
 * Screen Rows:The number of text rows in the current mode. Reserved (0).
 * Screen Columns:The number of text columns in the current mode. Reserved (0).


 * Parameter Packet Format

Set Variable Info returns with AX = 0 if it can successfully set the selected variable information. Otherwise, it returns with AX = ERROR_VIO_INVALID_PARMS.
 * Returns

There are two types of code page sets. The first code page set allows a code page to be set while the mode of the display (as used by Function 10Dh) remains the same. The other type of code page set causes a change in the display mode. This occurs when switching between DBCS and non-DBCS code pages.
 * Remarks

If bit 6 of the flags WORD is set and bit 7 is clear, the code page is set when the adapter can use the code page without changing from DBCS mode to SBCS mode, or vice versa. The mode should be changed if both bits 6 and 7 of the flags WORD are set, and the code page is used when the mode is changed from SBCS mode to DBCS mode. Bit 7 is ignored if bit 6 is not set. This applies only to text modes. Graphics modes are not set to text modes by forcing a code page.

The BVH need not support any scrollable region other than the entire display area. The adapter may support any scrollable rectangle up to the size of the entire screen. All coordinates are in text display cells. This scrollable rectangle data is undefined for graphics modes.

Function 114h
This function is used to notify the BVH that the environment is about to be freed so that any required cleanup can be performed by the BVH. If no Terminate Environment processing is required, this function can be omitted. PMERR_DEV_FUNC_NOT_INSTALLED is then returned in AX, but it is ignored by the video subsystem.
 * Terminate Environment - Function 114h
 * Parmlength :Length of parameter block in bytes (=6) passed on input.
 * Flags :Reserved, must be off.
 * Logical Buffer Selector :Selector used for the beginning of the logical video buffer. This selector is a huge selector with a maximum size of 1MB.


 * Parameter Packet Format


 * Returns:None.

Function 115h
This function causes the contents of the current screen to be written to the printer handle provided. BVS provides a default routine that provides the same level of support as previous versions if the vector is not replaced.
 * Print Screen - Function 115h
 * Parmlength :Length of parameter block in bytes (=8) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical video buffer should be printed.
 * OFF = Print only the contents of the logical video buffer.
 * ON = Print the contents of the physical video buffer, if appropriate.
 * Bits 1-15 are reserved and must be OFF.


 * Logical Buffer Selector :Selector used for the beginning of the logical video buffer. This selector is a huge selector with a maximum size of 1MB.
 * Print Device Handle :Print Device Handle. File handle of the print device to be used.


 * Parameter Packet Format


 * Returns:None.

Function 116h
This function performs the functions of the call to VioWrtTTY. BVS provides a default routine that provides the same level of support as previous versions if the vector is not replaced.
 * Write TTY - Function 116h
 * Parmlength :Length of parameter block in bytes (=14) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical video buffer needs to be updated.
 * OFF = The physical video buffer must not be updated.
 * ON = The physical video buffer must be updated.
 * Bit 1 indicates whether the logical video buffer needs to be updated.
 * OFF = The logical video buffer can optionally be updated.
 * ON = The logical video buffer must be updated.
 * Bit 2 indicates whether ANSI is active.
 * OFF = ANSI is not active. Escape sequences should be considered as text data.
 * ON = ANSI is active.  Escape sequences must be handled locally or passed to the default routine in BVS through device chaining.
 * Bit 3 indicates whether Ctrl_PrtSc is active.
 * OFF = Ctrl_PrtSc is not active.
 * ON = Ctrl_PrtSc is active.  Characters need to be echoed to the printer locally or by the default routine in BVS through device chaining.
 * Bits 4-15 are reserved and must be OFF.


 * Logical Buffer Selector :Selector used for the beginning of the logical video buffer. This selector is a huge selector with a maximum size of 1MB.
 * Character String Far Address :Far Address of character string to be written.
 * Character String Length :Length of character string to be written.
 * Print Device Handle :Print Device Handle. The file handle of the print device used for Ctrl_ PrtSc.


 * Parameter Packet Format


 * Returns:None.

Function 117h
This function returns information associated with the LVB, such as the allocation size and default attribute for a specified LVB.
 * Query LVB Info - Function 117h
 * Parmlength :Length of parameter block in bytes (=20) passed on input.
 * Flags :Defined as follows:
 * Bit 0 indicates whether the physical hardware is to be read.
 * OFF = Read from the environment buffer.
 * ON = Read from the current state of the hardware state.
 * Bits 1-15 are reserved and must be OFF.


 * LVB Format ID :Format ID for LVB. If this and the attribute count are both 0, the current mode values are used.
 * LVB Attribute Count :Attribute Count for the LVB. If this and the format ID are both 0, the current mode values are used.
 * LVB Width :LVB Width in cells.
 * LVB Height :LVB Height in cells.
 * LVB Allocation Size :Allocation size of the LVB is returned here.
 * Attribute Return Buffer Size :Size of the default attribute return buffer.
 * Attribute Return Buffer Pointer :Pointer to the default attribute return buffer (passed). The default attribute is returned if the buffer is large enough. If this value is 0, the attribute is not returned.


 * Parameter Packet Format

This function returns with AX = 0 if it can successfully calculate the LVB size and return the attribute information. Otherwise, it returns with AX = ERROR_VIO_INVALID_PARMS.
 * Returns

Level 0 Physical Device Driver Interfaces
The strategy portion of the Level 0 physical device drivers that can be a component of any video device handler is called to handle I/O requests through a request packet interface with the OS/2 kernel. The strategy routine executes at task-time as a result of an application VIO request. The strategy routine is called with ES:BX pointing to the request packet (the pointer is valid in both a DOS session and an OS/2 session). Only three command codes (passed in the request packet) are required to be supported by a video device driver. For any other command code the physical device driver does not support, the physical video device driver must return Unsupported Command and Done in the request packet status field.

The following are the physical device driver commands that are supported by the physical video device driver (the command codes are in parentheses):

INIT (00h) - Initialize the Device
On entry, the request block contains the following fields as inputs to the physical video device driver:
 * Pointer to the DevHlp entry point
 * Pointer to the INIT arguments

On exit, the physical video device driver sets the first pointer to the offsets of the code and data segments to release code and data needed only by the initialization routine. The second pointer is set to 0. If initialization is successful, the request packet status field is set to indicate No Error and Done; otherwise, the status is set to General Failure.

The physical video device driver can perform the following initialization:
 * Obtain the DevHlp address from the request packet.
 * Verify that the display adapter and the display that it supports are present. If not, it can fail initialization.

OPEN (0Dh) - Open the Device
This service routine does nothing but return with No Error status.

GENERIC IOCtl (10h) - Send I/O Requests to the Device
On entry, the request packet has the IOCtl category code and function code set. The parameter buffer and the data buffer addresses are set as virtual addresses. The physical video device driver performs the physical device driver initialization, when requested.

Physical Device Driver Initialization
The IOCtl described below supports the same class of functions as the Presentation Manager dynamic link enable entry point. It is called to fill in the Call Vector Table for the BVH. The call returns an error if the physical device driver detects that the adapter is not present.
 * Category 3 :Function 73h
 * Purpose :To initialize the Call Vector Table.
 * Parameter Block Format :None.
 * Data Packet Format :

Subfunction
 * DWORD||Subfunction
 * DWORD||Parameter1
 * DWORD||Parameter2
 * WORD||ReturnCode
 * }
 * WORD||ReturnCode
 * }
 * }

The Presentation Manager enables the subfunction number. Its value must be 1 to start the Presentation Manager Fill Logical Device Block subfunction. All pieces of the BVH must support this function. Pieces of the BVH that do not support the Presentation Manager interface do not need to support the other functions. Any function not supported should return PMERR_DEV_FUNC_NOT_INSTALLED.

Parameter1 for Subfunction = 1

Far pointer to this structure:

Engine Version Version of the Presentation Manager Graphics Engine
 * DWORD||Engine Version
 * DWORD||Count of Table Functions
 * }
 * }

Count of Table Functions Number of entries in the passed dispatch table. The physical device driver can only write this many entries into the table.

Parameter2 for Subfunction=1

Far pointer to this structure:

Flags Pointer Pointer to where the flags controlling calls to the Fill Physical Device Block function go.
 * DWORD||Flags Pointer
 * DWORD||Call Vector Table
 * }
 * }

Call Vector Table Pointer to the default dispatch table containing the addresses of the default handler functions and the functions supported by this component. Each entry in the Call Vector Table is the far address of a Video Device Handler function, which must be callable from Ring 3. The address of the nth BVH function is the nth DWORD in the table, beginning with Function 0. Refer to the DLL Initialization function for a description of the function numbers.

Remarks
This function is supported by the video device drivers and is called only once for each adapter to be supported by the BVH. A video device handler should determine if the display adapter and that which it supports is present. If not present, this function must return an error. Every part of a BVH must successfully initialize the Call Vector Table for that device to be used by OS/2.

EGA.SYS and INT 2Fh Screen Switch Notification
For some DOS EGA applications, OS/2 is not able to switch from a DOS session to an OS/2 session and then back again. Upon return to the DOS application, the screen will be incorrect. The DOS EGA applications that do not run successfully are:
 * Applications that download fonts into a character generator block other than Block 0. Character Generator Block 0 is supported.
 * Graphic mode applications that use more than one display page.
 * Advanced graphics mode applications that write directly to the registers on the EGA adapter.

To supplement OS/2 screen switching support, a DOS application can be written to use the EGA register interface. Alternatively, a DOS application can be notified on a screen switch through multiplex interrupt 2Fh, AH = 40h. These two mechanisms are described in the following sections.

Note: On an IBM PS/2 personal computer the registers on the adapter are both readable and writable. For these configurations, OS/2 reads and saves the registers on a screen switch away from a DOS session, and restores the registers upon return to a DOS session.

For configurations including the IBM PS/2 Display Adapter 8514/A when the 8514/A display adapter is in an advanced function mode, the OS/2 operating system does not save the physical display buffer when switching away from a DOS session. Therefore, end users are cautioned to complete any 8514/A advanced function mode application before switching to OS/2 mode.

EGA.SYS Device Driver
EGA.SYS is a physical device driver that provides support for the EGA register interface in a DOS session. To support advanced graphics modes D, E, F, and 10 in a DOS session, the Mouse Pointer Draw device driver must save or restore the EGA registers. Because the EGA registers are not readable, this can be done only if the application assists in setting the registers initially. Rather than performing I/O directly to the registers on the adapter, the application sets the registers through the EGA register interface.

EGA Register Interface
The EGA register interface is a library of ten functions supported for a DOS session, advanced graphics applications (modes D, E, F, and 10). These functions do the following:
 * Read from, or write to, one or more of the EGA write-only registers
 * Define default values for the EGA write-only registers, reset the EGA registers to these default values, or return the default values
 * Check whether the EGA register interface is present and, if so, return its version number.

When the application uses the EGA register interface, OS/2 2.1 maintains a backup copy or shadows how the EGA registers are set. Then, if the operator switches away from (and later returns to) the application, the registers are restored properly. It is not necessary to use the EGA register interface to set the mode, color palette, or palette registers. Instead, use ROM BIOS function INT 10h with AH = 00h, 0Bh, or 10h, respectively.

Calling The EGA Register Interface
To call EGA register interface functions from an assembly language program, the following actions must be performed: Values returned by the EGA register interface functions are placed in registers.
 * 1) Load the registers with the required parameter values
 * 2) Execute software interrupt 10h.

EGA Register Interface Restrictions
A list of areas where restrictions apply for the EGA Register Interface are shown below: ?Attribute Controller registers
 * Functions not supported
 * Sequencer Memory Mode register
 * Input Status registers
 * Graphics Controller Miscellaneous register

Functions Not Supported

Multiple display pages in graphics modes are not supported. Fonts can be loaded (by using ROM BIOS INT 10h with AH = 11h) only into Character Generator Block 0.

Attribute Controller Registers

Before your application program uses the Attribute Controller registers (I/ O address 3C0h) in an extended interrupt 10h call, it must set the flip-flop that selects the address or data register so that it selects the address register (by doing an input from I/O port 3BAh or 3DAh). The flip- flop is always reset to this state upon return from the extended INT 10h call. Interrupt routines that access the attribute chip must also leave the flip-flop set to the address register upon return from the interrupt.

Note: If the application program sets the flip-flop so that it selects the Data register, and expects the flip-flop to remain in this state, the application must disable interrupts between the time it sets the flip-flop to the Data register state and the last time the flip-flop is assumed to be in this state.

Sequencer Memory Mode Register

When the Sequencer Memory Mode register (I/O address 3C5H, data register 4) is accessed, the sequencer produces a faulton the CAS lines that can cause problems with video random access memory. As a result, the application cannot use the EGA Register Interface to read from, or write to, this register. Instead, use the following procedure to safely alter this register:
 * 1) Disable interrupts
 * 2) Set Synchronous Reset (bit 1) in the Sequencer Reset register to 0
 * 3) 3.Read/modify/write the Sequencer Memory Mode register
 * 4) 4.Set Synchronous Reset (bit 1) in the Sequencer Reset register to 1
 * 5) 5.Enable interrupts

Input Status Registers

The application cannot use the EGA Register Interface to read Input Status registers 0 (I/O address 3C2h) and 1 (I/O address 3BAh or 3DAh). If the program must read these registers, it must do so directly.

Graphics Controller Miscellaneous Register

When the Graphics Controller Miscellaneous register (I/O address 3CFh, data register 6) is accessed, a glitch on the CAS lines occurs that can cause problems with video random access memory. As a result, the application should not use the EGA Register Interface to read from or write to this register.

EGA Register Interface Function F6h does not alter the state of the Graphics Controller Miscellaneous register. Instead, use the following procedure to safely alter this register:
 * 1) Disable interrupts
 * 2) Set Synchronous Reset (bit 1) in the Sequencer Reset register to 0
 * 3) Read/modify/write the Graphics Controller Miscellaneous register
 * 4) Set Synchronous Reset (bit 1) in the Sequencer Reset register to 1
 * 5) Enable interrupts

EGA Register Interface Functions
This section describes each EGA Register Interface function in detail. The following list shows these functions by function number (hex):
 * F0 Read One Register
 * F1 Write One Register
 * F2 Read Register Range
 * F3 Write Register Range
 * F4 Read Register Set
 * F5 Write Register Set
 * F6 Revert to Default Registers
 * F7 Define Default Register Table
 * F8 Read Default Register Table
 * FA Interrogate Driver

Note: Function F9h, and Functions FBh through FFh are reserved.

Each function description includes:
 * The parameters required to make the call (input) and the expected return values (output)
 * Any special considerations regarding the function

If the function description does not specify an input for a parameter, it is not necessary to supply a value for that parameter before making the call. If the function description does not specify an output value for a parameter, the parameter's value is the same before and after the call.

Note: The EGA Register Interface does not check input values, so be sure that the values loaded into the registers before making a call are correct.

Function F0H - Read One Register
This function reads data from a specified register on the EGA.

AH = F0h
 * Input

BX = Pointer for:
 * Pointer/data chips
 * {|BH =||0


 * BL =||Pointer
 * }
 * Single registers
 * BX ignored.
 * BX ignored.

DX = Port number:
 * Pointer/data chips


 * 0h:||CRT Controller (3?4H)
 * 8h:||Sequencer (3C4H)
 * 10h:||Graphics Controller (3CEH)
 * 18h:||Attribute Controller (3C0H)
 * }
 * Single registers
 * 18h:||Attribute Controller (3C0H)
 * }
 * Single registers

? = B for monochrome modes, or D for color modes AX: Restored
 * 20h:||Miscellaneous Output register (3C2H)
 * 28h:||Feature Control register (3?AH)
 * 30h:||Graphics 1 Position register (3CCH)
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * }
 * Output

BH: Restored

BL: Data

DX: Restored

All other registers are restored.

The following example saves the contents of the Sequencer Map Mask register in myvalue: myvalue db  ? mov ah, 0f0h        ; f0 = read one register mov bx, 0002h       ; bh = 0 / bl = map mask index mov dx, 0008h       ; dx = sequencer int 10h             ; get it! mov myvalue, bl     ; save it! The example below saves the contents of the Miscellaneous Output register in myvalue: myvalue db  ? mov ah, 0f0h        ; f0 = read one register mov dx, 0020h       ; dx = miscellaneous output register int 10h             ; get it! mov myvalue, bl     ; save it!
 * Example

Function F1H - Write One Register
This function writes data to a specified register on the EGA. When an application program returns from a call to Function F1, the contents of registers BH and DX are not restored. The program must save and restore these registers.
 * Input

AH = F1h

BL = Pointer for pointer/data chips. Data for single registers.

BH = Data for pointer/data chips. Ignored for single registers.

DX = Port number:
 * Pointer/data chips


 * 0h:||CRT Controller (3?4H)
 * 8h:||Sequencer (3C4H)
 * 10h:||Graphics Controller (3CEH)
 * 18h:||Attribute Controller (3C0H)
 * }
 * Single registers
 * 18h:||Attribute Controller (3C0H)
 * }
 * Single registers

? = B for monochrome modes or D for color modes AX: Restored
 * 20h:||Miscellaneous Output register (3C2H)
 * 28h:||Feature Control register (3?AH)
 * 30h: Graphics 1 Position register (3CCH)
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * 30h: Graphics 1 Position register (3CCH)
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * }
 * Output

BL: Restored

BH: Not restored

DX: Not restored

All other registers are restored.

The following example writes the contents of myvalue into the CRT Controller Cursor Start register: myvalue db  3h mov ah, 0f1h        ; f1 = write one register mov bh, myvalue     ; bh = data from myvalue mov bl, 000ah       ; bl = cursor start index mov dx, 0000h       ; dx = crt controller int 10h             ; write it! The example below writes the contents of myvalue into the Feature Control register: myvalue db  2h mov ah, 0f1h        ; f1 = write one register mov bl, myvalue     ; bl = data from myvalue mov dx, 0028h       ; dx = feature control register int 10h             ; write it!
 * Example

Function F2H - Read Register Range
This function reads data from a specified range of registers on the EGA. A range of registers is defined to be several registers that have consecutive indexes, on a single chip. This function is applicable for pointer/data chips. AH = F2h
 * Input

CH = Starting pointer value

CL = Number of registers (must be >1)

DX = Port number:
 * Pointer/data chips

? = B for monochrome modes, or D for color modes
 * 0h:||CRT Controller (3?4H)
 * 8h:||Sequencer (3C4H)
 * 10h:||Graphics Controller (3CEH)
 * 18h:||Attribute Controller (3C0H)
 * }
 * 18h:||Attribute Controller (3C0H)
 * }
 * }

ES:BX = Points to table of one-byte entries (length = value in CL). On return, each entry is set to the contents of the corresponding register. AX: Restored
 * Output

BX: Restored

CX: Not restored

DX: Restored

ES: Restored

All other registers are restored.

The following example saves the contents of the Attribute Controller Palette registers in paltable: paltable db 16 dup (?) mov ax, ds               ; assume paltable in data segment mov es, ax               ; es = data segment mov bx, offset paltable  ; es:bx = paltable address mov ah, 0f2h             ; f2 = read register range mov cx, 0010h            ; ch = start index of 0 ; cl = 16 registers to read mov dx, 0018h            ; dx = attribute controller int 10h                  ; read them!
 * Example

Function F3H - Write Register Range
This function writes data to a specified range of registers on the EGA. A range of registers is defined to be several registers that have consecutive indexes, on a single chip. This function is applicable for the pointer/data chips. AH = F3h
 * Input

CH = Starting pointer value

CL = Number of registers (must be >1)

DX = Port number:
 * Pointer/data chips
 * {|0h:||CRT Controller (3?4H)

? = B for monochrome modes, or D for color modes
 * 8h:||Sequencer (3C4H)
 * 10h:||Graphics Controller (3CEH)
 * 18h:||Attribute Controller (3C0H)
 * }
 * 18h:||Attribute Controller (3C0H)
 * }
 * }

ES:BX = Points to table of one-byte entries (length = value in CL). Each entry contains the value to be written to the corresponding register. AX: Restored
 * Output

BX: Not restored

CX: Not restored

DX: Not restored

ES: Restored.

All other registers are restored.

The following example writes the contents of cursloc into the CRT Controller Cursor Location High and Cursor Location Low registers. cursloc db  01h, 00h            ; cursor at page offset 0100h mov ax, ds              ; assume cursloc in data segment mov es, ax              ; es = data segment mov bx, offset cursloc  ; es:bx = cursloc address mov ah, 0f3h            ; f3 = write register range mov cx, 0e02h           ; ch = start index of 14 ; cl = 2 registers to write mov dx, 0000h           ; dx = crt controller int 10h                 ; write them!
 * Example

Function F4H - Read Register Set
This function reads data from a set of registers on the EGA. A set of registers is defined to be several registers that might have consecutive indexes and that might not be on the same chip. AH = F4h
 * Input

CX = Number of registers (must be >1)

ES:BX = Points to table of records with each entry in this format:

Bytes 1-2: Port number:
 * Pointer/data chips

18h:||Attribute Controller (3C0H)
 * 0h:||CRT Controller (3?4H)
 * 8h:||Sequencer (3C4H)
 * 10h:||Graphics Controller (3CEH)
 * 10h:||Graphics Controller (3CEH)
 * 10h:||Graphics Controller (3CEH)
 * }
 * Single registers

? = B for monochrome modes, or D for color modes
 * 20h:||Miscellaneous Output register (3C2H)
 * 28h:||Feature Control register (3?AH)
 * 30h:||Graphics 1 Position register (3CCH)
 * 38h: Graphics 2 Position register (3CAH)
 * }
 * 38h: Graphics 2 Position register (3CAH)
 * }
 * }

Byte 3: Pointer value (0 for single registers)

Byte 4: EGA Register Interface fills in data read from register specified in bytes 1-3. AX: Restored
 * Output

BX: Restored

CX: Not restored

ES: Restored.

All other registers are restored.

The following example saves the contents of the Miscellaneous Output register, Sequencer Memory Mode register, and CRT Controller Mode Control register in results: outvals dw  0020h               ; miscellaneous output register db  0                   ; 0 for single registers db  ? ; returned value dw  0008h               ; sequencer db  04h                 ; memory mode register index db  ? ; returned value dw  0000h               ; crt controller db  17h                 ; mode control register index db  ? ; returned value
 * Example

results db  3 dup (?) mov ax, ds              ; assume outvals in data segment mov es, ax              ; es = data segment mov bx, offset outvals  ; es:bx = outvals address mov ah, 0f4h            ; f4 = read register set mov cx, 3               ; number of entries in outvals int 10h                 ; get values into outvals mov si, 3               ; move the returned values from add si, offset outvals  ;  outvals mov di, offset results  ;  to results mov cx, 3               ; 3 values to move

loop:  mov  al, [si]            ; move one value from mov [di], al            ;  outvals to results add si, 4               ; skip to next source byte inc di                  ; point to next destination byte loop loop

Function F5H - Write Register Set
This function writes data to a set of registers on the EGA. A set of registers is defined to be several registers that might have consecutive indexes, and that might be on the same chip. AH = F5h
 * Input

CX = Number of registers (must be >1)

ES:BX = Points to table of values with each entry in this format:

Bytes 1-2: Port number:
 * Pointer/data chips


 * 0h:||CRT Controller (3?4H)
 * 8h:||Sequencer (3C4H)
 * 10h:||Graphics Controller (3CEH)
 * 18h:||Attribute Controller (3C0H)
 * }
 * Single registers
 * 18h:||Attribute Controller (3C0H)
 * }
 * Single registers

? = B for monochrome modes, or D for color modes
 * 20h:||Miscellaneous Output register (3C2H)
 * 28h:||Feature Control register (3?AH)
 * 30h:||Graphics 1 Position register (3CCH)
 * 38h: Graphics 2 Position register (3CAH)
 * }
 * 38h: Graphics 2 Position register (3CAH)
 * }
 * }

Byte 3: Pointer value (0 for single registers)

Byte 4: Data to be written to register specified in bytes 1-3.
 * Output
 * AX: Restored
 * BX: Restored
 * CX: Not restored
 * ES: Restored.

All other registers are restored.

The following example writes the contents of outvals to the Miscellaneous Output register, Sequencer Memory Mode register, and CRT Controller Mode Control register: outvals dw  0020h               ; miscellaneous output register db  0                   ; 0 for single registers db  0a7h                ; output value dw  0008h               ; sequencer db  04h                 ; memory mode register index db  03h                 ; output value dw  0000h               ; crt controller db  17h                 ; mode control register index db  0a3h                ; output value mov ax, ds              ; assume outvals in data segment mov es, ax              ; es = data segment mov bx, offset outvals  ; es:bx = outvals address mov ah, 0f5h            ; f5 = write register set mov cx, 3               ; number of entries in outvals int 10h                 ; write the registers!
 * Example

Function F6H - Revert to Default Registers
This function restores the default settings of any registers that the application program has changed through the EGA Register Interface. The default settings are defined in a call to Function F7 (described in the next section). AH = F6h All registers are restored. The following example restores the default settings of the EGA registers: mov ah, 0f6h    ; f6 = revert to default registers int 10h         ; do it now!
 * Input
 * Output
 * Example

Function F7H - Define Default Register Table
This function defines a table containing default values for any pointer/data chip or single register. If default values are defined for a pointer/data chip, they must be defined for all registers within that chip. AH = F7h
 * Input

DX = Port number:
 * Pointer/data chips

? = B for monochrome modes, or D for color modes
 * 0h:||CRT Controller (3?4H)
 * 8h:||Sequencer (3C4H)
 * 10h:||Graphics Controller (3CEH)
 * 18h:||Attribute Controller (3C0H)
 * }
 * Single registers
 * 20h:||Miscellaneous Output register (3C2H)
 * 28h: Feature Control register (3?AH)
 * 30h:||Graphics 1 Position register (3CCH)
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * 28h: Feature Control register (3?AH)
 * 30h:||Graphics 1 Position register (3CCH)
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * }

ES:BX = Points to table of one-byte entries. Each entry contains the default value for the corresponding register. The table must contain entries for all registers.


 * Output
 * AX: Restored
 * BX: Not restored
 * DX: Not restored
 * ES: Restored

All other registers are restored.

The following example defines default values for the Attribute Controller: attrdflt db 00h, 01h, 02h, 03h, 04h, 05h, 06h, 07h db 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h db 08h, 00h, 0fh, 00h mov ax, ds              ; assume attrdflt in data segment mov es, ax              ; es = data segment mov bx, offset attrdflt ; es:bx = attrdflt address mov ah, 0f7h            ; f7 = define default register table mov dx, 0018h           ; dx = attribute controller int 10h                 ; do it! The example below defines a default value for the Feature Control register: featdflt db 00h mov ax, ds              ; assume featdflt in data segment mov es, ax              ; es = data segment mov bx, offset featdflt ; es:bx = featdflt address mov ah, 0f7h            ; f7 = define default register table mov dx, 0028h           ; dx = feature control register int 10h                 ; do it!
 * Example

Function F8H - Read Default Register Table
This function reads the table containing default register values for any pointer/data chip or single register.

AH = 0F8H
 * Input

DX = Port number:
 * Pointer/data chips


 * 0h:||CRT Controller (3?4H)
 * 8h:||Sequencer (3C4H)
 * 10h||Graphics Controller (3CEH)
 * 18h||Attribute Controller (3C0H)
 * }
 * Single registers
 * 18h||Attribute Controller (3C0H)
 * }
 * Single registers

? = B for monochrome modes, or D for color modes
 * 20h:||Miscellaneous Output register (3C2H)
 * 28h:||Feature Control register (3?AH)
 * 30h:||Graphics 1 Position register (3CCH)
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * 38h:||Graphics 2 Position register (3CAH)
 * }
 * }

ES:BX = Points to a table into which the default values are returned. The table must have room for the full set of values for the pointer/data chip or single register specified.


 * Output:
 * AX: Restored
 * BX: Not restored
 * DX: Not restored
 * ES: Restored

All other registers are restored.

The following example reads the default values for the Miscellaneous Output register: regdflt db         mov  ax, ds         mov  es, ax               ; es = data segment mov bx, offset regdflt   ; es:bx = regdflt address mov ah, 0f8h             ; f8 = read default register table mov dx, 0020h            ; dx = miscellaneous output register int 10h                  ; do it! The following example reads the default values for the CRT Controller register: regdflt db   25 dup (?) mov ax, ds         mov  es, ax               ; es = data segment mov bx, offset regdflt   ; es:bx = regdflt address mov ah, 0f8h             ; f8 = read default register table mov dx, 0000h            ; dx = crt controller register int 10h                  ; do it!
 * Example

Function FAH - Interrogate Driver
This function returns a value specifying whether the EGA.SYS device driver is present.
 * Input
 * AH = FAh
 * BX = 0


 * Output
 * AX: Restored
 * BX: 0, if EGA.SYS driver is not present
 * ES:BX: Pointer to EGA Register Interface version number, if present
 * Byte 1: Major release number
 * Byte 2: Minor release number (in 1/100ths)

The following example interrogates the driver and displays the results: gotmsg db   "EGA.SYS driver found", 0dh, 0ah, 24h nopmsg db   "EGA.SYS driver not found", 0dh, 0ah, 24h revmsg db   "revision $" crlf   db   0dh, 0ah, 24h ten    db   10 mov bx, 0              ; must be 0 for this call mov ah, 0fah           ; fa = interrogate driver int 10h                ; interrogate! or  bx, bx             ; bx = 0 ? jnz found              ; branch if driver present mov dx, offset nopmsg  ; assume nopmsg in data segment mov ah, 09h            ; 9 = print string int 21h                ; output not found message jmp continue           ; that's all for now found: mov  dx, offset gotmsg  ; assume gotmsg in data segment mov ah, 09h            ; 9 = print string int 21h                ; output found message mov dx, offset revmsg  ; assume revmsg in data segment mov ah, 09h            ; 9 = print string int 21h                ; output "revision " mov dl, es:[bx]        ; dl = major release number add dl, "0"            ; convert to ASCII mov ah, 2              ; 2 = display character int 21h                ; output major release number mov dl, "." ; dl = "." mov ah, 2              ; 2 = display character int 21h                ; output a period mov al, es:[bx+1]      ; al = minor release number
 * Example

xor ah, ah             ; ah = 0 idiv ten               ; al = 10ths, ah = 100ths mov bx, ax             ; save ax in bx        mov  dl, al             ; dl = 10ths add dl, "0"            ; convert to ASCII mov ah, 2              ; 2 = display character int 21h                ; output minor release 10ths mov dl, bh             ; dl = 100ths add dl, "0"            ; convert to ASCII mov ah, 2              ; 2 = display character int 21h                ; output minor release 100ths mov dx, offset crlf    ; assume crlf in data segment mov ah, 09h            ; 9 = print string int 21h                ; output end of line continue:                      ; the end

INT 2Fh Screen Switch Notification
A new Multiplex Interrupt (INT 2Fh) is issued by OS/2 to signal either of the following two events:
 * Switching the DOS application to the background (AX = 4001H)
 * Switching the DOS application to the foreground (AX = 4002H)

A DOS application that receives this signal must hook the Multiplex Interrupt vector. That is, when the application is started, it must save the current INT 2Fh vector and set this vector to point to the application's interrupt handler.

When the notification is received, the application must save all registers, perform whatever processing is required, restore all registers, and issue the IRET instruction to return to the operating system. Only the following forms of processing are supported:
 * Modifying application or video memory (or both)
 * Issuing ROM BIOS video service calls (INT 10h)
 * Issuing EGA Register Interface calls (INT 10h)
 * Programming the EGA video card directly

Note: When an application is being switched to the background, and the application's INT 2Fh handler uses the EGA Register Interface to save the EGA registers, these registers are restored automatically when the application is returned to the foreground.

An application can receive notification that it is being switched to the background at any time. Code sequences that are sensitive to interruption can be protected with CLI/STI instructions. When the switch notification occurs, the application (other than its INT 2Fh handler) is frozen until it is returned to the foreground.

When an application's INT 2Fh handler receives notification with a value in AH other than 40H, the application must issue the JMP FAR instruction to branch to the previous INT 2Fh vector.

Using Extended Screen and Keyboard Control (ANSI.SYS, ANSICALL)
This section explains how to issue special control character sequences to:
 * Control the position of the cursor
 * Erase text from the screen
 * Set the display mode
 * Redefine the meaning of keyboard keys

ANSI extended screen and keyboard control sequences are supported in DOS sessions by ANSI.SYS, an installable device driver. In OS/2 sessions, these control sequences are supported by the ANSICALL component within OS/2 CHAR. DLL.

Note: In this section, unless otherwise specified, ANSI refers to both ANSI.SYS and ANSICALL.

Limitations and Restrictions
ANSI operates on a per-session basis. OS/2-mode ANSI is affected when keys are reassigned in a code page environment. ANSI does not provide code page support for key reassignment in a DOS session.

Control Sequence Syntax
Each of the cursor control sequences is in the format:
 * ESC [ parameters COMMAND

A cursor control sequence is defined as follows: For example, ESC [2;10H could be created using BASIC as shown below. Notice that "CHR$(27)" is ESC. The IBM Personal Computer Basic Version 3.00 Copyright IBM Corp. 1981, 1982, 1983, 1984 xxxxx Bytes free

OK open "sample" for output as 1 OK print #1, CHR$(27);"[2;10H";"x row 2 col 10" OK close #1 OK

Cursor Control Sequences
The following tables contain the cursor control sequences used to control cursor positioning:

This example copies the file SAMPLE from the previous example to CON, that places the cursor on row 2, column 10 of the screen:
 * type sample

Note: Do not use the Device Status Report as part of a prompt.

This example tells ANSI to put the current cursor position (row and column) in STDIN. Then the program reads it from STDIN and outputs it to STDOUT. PROGRAM dsr(INPUT,OUTPUT);

VAR f:FILE OF CHAR; key:CHAR;

FUNCTION inkey:CHAR;                   { read character  } VAR                                  { from the  /Using a File ch:CHAR;                           { keyboard buffer } BEGIN READ(f,ch); inkey:=ch END;

BEGIN ASSIGN(f,'user'); RESET(f); WRITE(CHR(27),'[6n');            { issue a DSR,  } key:=inkey;                      { read up to    } key:=inkey;                      { first digit   } key:=inkey;                      { of the row    } WRITE('row ',inkey,inkey,' column '); key:=inkey;                      { skip to column} WRITE(inkey,inkey)               { write column  } END.

Erasing
The following tables contain the control sequences used to erase text from the screen:

Controlling the Display Mode
The following tables contain the control sequences used to set the mode of operation:
 * Set Graphics Rendition (SGR)
 * Set Mode (SM)
 * Reset Mode (RM)

Keyboard Key Reassignment
The ANSI system can be used to reassign keys on the keyboard. When an application calls KbdStringIn, the reassigned key's ASCII code is converted to the specified string and is passed back to the calling application. For example, replace a with q so that whenever the a key is pressed, a q is passed to the application that is reading input.

In OS/2 2.1, keyboard remapping can be done only from an application calling KbdStringIn. In DOS, keyboard remapping must be done from the command line.

Note: Keyboard reassignment works only with OS/2 applications that use the KbdStringIn call to get input.

OS/2 mode ANSI is affected when keys are reassigned in a code-page environment. ANSI "remembers" the code page under which a key is reassigned. The keyboard subsystem checks for reassigned keys when the application calls the KbdStringIn function. When a reassigned key is detected, the ANSI support:
 * 1) Checks to see what code page the requestor is running under
 * 2) Looks internally to see if the key has been reassigned under that code page
 * 3) If there is a key reassignment for that code page, gives the reassignment string
 * 4) Otherwise, gives the original ASCII codes.

A maximum storage of 64KB can be allocated to OS/2 mode ANSI-reassigned key definitions. The table shown below contains the control sequences used to redefine the meaning of keyboard keys: To execute the examples below, either create a file that contains the following statements and then use the TYPE command to display the file that contains the statement, or execute the command at the OS/2 prompt:
 * Assign the Aand akey to the Qand qkey, respectively.
 * Assign the Qand qkey to the Aand akey, respectively:

Using a File: ESC [65;8lp         A becomes Q ESC [97;113p         a becomes q ESC [81;65p          Q becomes A ESC [113;97p         q becomes a At the OS/2 Prompt: prompt $e[65;8lp    A becomes Q prompt $e[97;113p    a becomes q prompt $e[81;65p     Q becomes A prompt $e[113;97p    q becomes a
 * Reassign the F10 key to a DIR command followed by a carriage return:

Using a File:

ESC [0;68;"dir";13p

At the OS/2 Prompt:

prompt $e[0;68;"dir";13p

The $e is the prompt command characters for ESC. The 0;68 is the extended ASCII code for the F10 key; 13 decimal is a carriage return.
 * The following example sets the prompt to display the current directory on the top of the screen and the current drive on the current line:

prompt $e[s$e[1;30f$e[K$p$e[u$n$g

If the current directory is C:\FILES, and the current drive is C, this example would display: C:\FILES C>
 * The following DOS-compatible assembly language program reassigns the F10 key to a DIR B: command followed by a carriage return:

TITLE SET ANSI.ASM - SET F10 TO STRING FOR ANSI.SYS

CSEG   SEGMENT PARA PUBLIC 'CODE' ASSUME CS:CSEG,DS:CSEG ORG    100H ENTPT: JMP     SHORT START STRING DB      27,'[0;68;"DIR B:";13P' ;Redefine F10 key STRSIZ EQU     $-STRING                ;Length of above message HANDLE EQU     1                       ;Pre-defined file. ;Handle for standard output

START  PROC    NEAR MOV    BX,HANDLE               ;Standard output device MOV    CX,STRSIZ               ;Get size of text to be sent MOV    DX,OFFSET STRING        ;Pass offset of string ;To be sent MOV    AH,40H                  ;Function="write to device" INT    21h                     ;Call DOS RET                            ;Return to DOS START  ENDP

CSEG   ENDS END    ENTPT

DPRINTF Print Formatting Package
DPRINTF is a kernel-debugging print-formatting package. You can include this function in the code to test your display driver.

To use the DPRINTF function, you must have a second device attached to COM1 or COM2. Due to difficulties passing variable-length argument lists through a call-gate transition, only one argument, a 0-terminated string, is passed to this routine. The string is sent to either COM1 or COM2 depending on how the variable, UR_DAT, is defined.

The only checking that this routine performs is to process XON/XOFF characters from the equipment attached to the debug port. This guarantees that the output does not overrun the receiving device. However, after receiving XOFF, this routine spins in a loop, waiting for XON.

The string to be output is ASCIIZ. It may contain literal characters.

A literal character is defined as any character that is not part of a format specification. Special non-printing characters are listed as follows:
 * \n for CRLF (carriage return/linefeed)
 * \t for tab
 * \b for bell
 * \\ for \.