Windows Instrumentation: WMI and ACPI

This article describes the process that system manufacturers (OEMs) can use to provide instrumentation information by including ACPI objects in the systems they build that will be recognized by Microsoft Windows Management Instrumentation (WMI). This information applies for Windows 2000, Windows XP, and Windows 98 Second Edition. By including ACPI objects in the systems they build, OEMs can take advantage of a generic mapping driver that allows WMI to make the information available to the instrumentation consumers.

Archived paper. No warranty is made as to technical accuracy of content or currency of URLs.

The ACPI subsystem contains a wealth of instrumentation information; OEMs are encouraged to use ACPI to add additional platform specific instrumentation information. However, ACPI objects are not readily accessible by instrumentation data consumers such as WBEM.

This article assumes the reader is familiar with driver mapping under Windows operating systems and the Data Block GUID Mapping control method for WMI. For information about WMI technologies for system management and hardware instrumentation, see https://msdn.microsoft.com/windows/hardware/gg463463. ACPI implementation information is available at https://www.acpi.info/ .

Technology Overview for Windows Instrumentation

The ACPI-to-WMI mapping functionality is achieved by means of two device drivers provided with the Windows 2000, Windows XP, and Windows 98 Second Edition operating systems:

• Acpi.sys is the regular ACPI device driver with some modifications.

• Wmiacpi.sys registers with Plug and Play ID PNP0c14.

OEMs can differentiate their PC system capabilities by writing ACPI Source Language (ASL) code and a Managed Object Format (MOF or MOF) file. The MOF file can be in the BIOS or on disk. For more information about MOF, see the "MOF Data Types" section later in this article.

ASL code is never executed directly by the Wmiacpi.sys driver. ASL code is always executed by the Acpi.sys driver (see the ASL information at https://www.acpi.info/) . Wmiacpi.sys will invoke Acpi.sys to call control methods that access the management data exposed by the mapping driver.

Microsoft does not ship a MOF file that is associated with the Wmiacpi.sys driver. The only information surfaced through ACPI is the temperature zone information, which is surfaced through and associated with the Acpi.sys device driver.

WMI Overview for Windows Instrumentation

WMI organizes individual data items (properties) into data blocks (structures) that contain related information. Data blocks may have one or more data items. Each data item has a unique index within the data block, and each data block is named by a globally unique 128-bit number called a globally unique identifier (GUID). WMI can provide notifications to the data producer as to when to start and stop collecting the data items that compose a data block. WMI has no knowledge of the data format for individual data blocks.

WMI functionality allows for querying all instances of a data block or a single instance of a data block. It also allows for setting all data items in an instance of a data block or a single data item within a single instance of a data block.

In addition to queries and sets, WMI allows WMI method calls, which are functionally equivalent to an I/O control (IOCTL) call to a device. Each WMI method call is identified by a GUID and a method index for that GUID. All WMI method calls use one buffer for input and output parameters. WMI allows notifications of significant events to be delivered to interested user-mode applications. Each type of event is uniquely named by a GUID. Events may also carry a data block with additional information about the event. WMI can provide notifications to the event generator about when to enable and disable an event type.

WMI is an open architecture that allows OEMs to define their own data blocks, methods, and events. Along with the data that composes the custom data block, the OEM must also provide a description that generally represents how a data block or WMI method is mapped to a 2-character ID. This 2-character ID is part of the names of the control methods that act upon the data block.

For example, when a call is made to query about the data block represented by a WMI GUID, the mapper will evaluate the WQxx control method (where xx is the 2-character ID mapped to that GUID). These mappings are defined by the ACPI code and obtained by the mapper evaluating the _WDG control method. For more information, see "ACPI Control Method Naming Conventions and Functionality" later in this article.

The mapping process is similar for events. The _WDG control method provides a mapping between the WMI event GUID that represents the event and the notification code specified in the ASL notify instruction. For example, when ACPI provides a callback to the mapper that a control method executed a notify(mapper-device, 0x81) function, the mapper will look up the WMI GUID mapped to 0x81 and use this WMI GUID in building the WMI event. Before launching the WMI event, the mapper will evaluate _WED to retrieve any additional data that belongs with the event.

Loading the Mapping Driver. The Plug and Play ID PNP0c14 is assigned as the WMI-mapping pseudo device; the operating system device INFs (Plug and Play ID-to-device driver lookup table) point this Plug and Play ID to the ACPI-to-WMI mapping driver. To cause the ACPI-to-WMI mapping driver to load, an ACPI system needs to define one or more devices with that Plug and Play ID in the ACPI device tree. Each device declared in the ACPI device tree would have its own operating system device object with its own set of mappings.

In this way, different sets of data blocks can be organized in the appropriate place within the device tree. This organization allows the different devices and their corresponding data blocks to come and go from the ACPI device tree. Note that if there are multiple WMI-mapping pseudo devices in the ACPI device tree, each device must have a unique value for its _UID.

Mapping Driver Functionality. Essentially the mapping driver will do the following:

• Manage all registration and unregistration with WMI and other interactions with the operating system. This registration of data and data blocks is done when the mapper gets the IRP_MN_REGINFO IRP.

• At WMI initialization time, the mapping driver will query an ACPI method for the list of data block, event, and method GUIDs it supports, as well as the mapping from the GUID to control method IDs. With this information, the mapping driver will register those GUIDs with WMI.

• Translate data block queries, sets, and method call I/O IRPs into the appropriate ACPI control method call.

• Receive notifications from the ACPI event handler control methods and relaunch them as WMI events.

• Translate strings between ASCIZ and UNICODE for data blocks marked as wholly composed of a string.

ACPI-to-WMI Mapper Goals for Windows Instrumentation

The following list describes the goals for the ACPI-to-WMI mapper:

• Expose data maintained by the hardware or firmware and accessible through ACPI to user-mode instrumentation data consumers, such as WBEM or DMI.

• Allow specific ACPI control methods to be called from a user-mode instrumentation data consumer or hardware configuration application--for example, from a control panel applet.

• Deliver specific ACPI events to all user-mode callers that request notification of that particular event.

• Allow OEMs to include OEM-specific data blocks, user-mode-callable ACPI control methods, and events without requiring any changes to the ACPI-to-WMI mapper.

• Allow general-purpose data consumer applications--those written without any special knowledge of the data blocks exposed by a particular machine--to be able to access and understand the data blocks, user-mode-callable ACPI control methods, and events being mapped--including those that are OEM specific.

• Define standard data block formats, user-mode-callable ACPI control methods, events and their WMI GUID mappings for common data blocks, and callable control methods and events expected to be provided by all OEMs. This can include dynamic data and functions identified by the industry in the SMBIOS specification and other specifications.

These goals are achieved by having supporting code in the ACPI-to-WMI mapper (Wmiacpi.sys) as well as in the core ACPI code itself (Acpi.sys).

The following are not goals for the ACPI-to-WMI mapper:

• To have specific knowledge about any data block that passes through the mapper.

• To provide interfaces specifically for SMBIOS data and functions. The mapper is an open architecture that is not restricted to SMBIOS data and functionality.

How SMBIOS-provided information is handled. Vendors who want to provide OEM and system-specific instrumentation data may choose to use SMBIOS as the mechanism. To use the capabilities of the WMI infrastructure to surface this SMBIOS data, they must conform to any SMBIOS version between 2.0 and 2.3. This allows the Microsoft Win32 provider--which is shipped with Windows 2000, Windows XP, and future versions of Windows, and which is available as an update to Windows 98--to populate almost all of the SMBIOS-provided information into the CIMv2 namespace. In particular, almost all of the information will be put into Win32 classes. Some of these Win32 classes are derived from the CIMv2.1 physical MOF.

The one exception where SMBIOS information will not be automatically populated by the Win32 provider into the CIMv2 namespace is SMBIOS vendor-specific data. Such SMBIOS vendor-defined data will be placed in a "VendorBucket" class in a "Root\VendorDefined" namespace, and will not be available in the CIMv2 namespace by default. Any system vendor who wants to provide such data must write a provider that will interpret this data.

The SMBIOS data is read only once, either at boot time in Windows 2000/Windows XP or post boot on Windows 98. Dynamic updates that are made to the SMBIOS data after it has been read will not be reflected in the namespaces in this implementation. Microsoft is working with the industry to define standard ACPI methods for dynamic updates.

The SMBIOS raw data will be available as a WMI data block in Windows 2000/Windows XP and as a flat file in Windows 98. This data will be interpreted and populated into the namespaces by the Win32 provider.

ACPI Control Method Naming Conventions and Functionality for Windows Instrumentation

The Data Block GUID Mapping control method named _WDG evaluates to a buffer that has the GUID mapping information for data blocks, events, and WMI methods. The result of the evaluation is a buffer containing an array of the following structure.

typedef struct
{
     GUID guid;             // GUID that names data block
     union
     {
         CHAR ObjectId[2];  // 2-character ACPI ID  (Data Blocks and Methods)
         struct 
         {
             UCHAR NotificationValue;  // Byte value passed by event handler control method
             UCHAR Reserved[1];
         } NotifyId;
    }
     USHORT InstanceCount;  // Number of separate instances of data block
     USHORT Flags;          // Flags
};
// Set this flag if the WCxx control method should be run to whenever the first 
// data consumer is interested in collecting the data block and whenever the last data 
// consumer is no longer interested.

#define WMIACPI_REGFLAG_EXPENSIVE   0x1

// Set this flag if the GUID represents a set of WMI method calls and not a data block

#define WMIACPI_REGFLAG_METHOD      0x2

// Set this flag if the data block is wholly composed of a string and should be 
// translated from ASCIZ to UNICODE in returning queries and from UNICODE to ASCIZ 
// when passing sets

#define WMIACPI_REGFLAG_STRING      0x04

// Set this flag if the guid maps to an event rather than a data block or method

#define WMIACPI_REGFLAG_EVENT       0x08

Each element in the array describes the mapping of a WMI data block GUID to a 2-letter ACPI method identifier used to compose the method names that operate on the data block or on the notification value used in the ASL Notify operation. Each element of the array also contains the number of instances of the data block that exist and any flags that are set.

This control method is required.

The following table summarizes the information for each control method described later in this section.

Control Method Summary

• Data Block Query Control Method. If the Data Block GUID Mapping control method describes a data block that does not have the WMIACPI_REG_METHOD flag set, there needs to be a control method that evaluates to the contents of an instance of the data block.

  By convention, the name of the object is WQ xx, where xx is the 2-character ID that maps to the GUID being queried. One parameter is passed to the method--the index of the instance, which is of type ULONG. Data blocks registered with only a single instance can ignore the parameter. If the result of the evaluation of the WQxx method is a string, then the mapper will convert that string to UNICODE so that it can be understood by WMI. This control method is required.

• Data Block Set Control Method. If the Data Block GUID Mapping control method describes a data block that does not have the WMIACPI_REG_METHOD flag set, there needs to be a control method that evaluates to the contents of an instance of the data block.

  By convention, the name of the object is WS xx, where xx is the 2-character ID that maps to the GUID being set. Two parameters are passed to the method; one is a ULONG that is the index of the instance, and the other is a buffer that contains the new values for the data block.

  If the GUID for the data block is registered with the WMIACPI_REGFLAG_STRING flag, then the mapper assumes that the data block passed is wholly composed of a single string and will convert that string from UNICODE to ASCIZ so that it can be understood by the WSxx control method. This control method is not required for those data blocks that are read only. Because the mapper is unaware of the format of the data block passed by the caller of the WMI method, it will pass the buffer as a single buffer parameter to the WM xx control method. The control method can use the ASL instructions CreateBitField, CreateDWordField, CreateField, and CreateWordFieldto break up the buffer into its parts.

• Data Item Set Control Method. Setting of individual data items within a data block is not supported. Typically, data items that can be modified should be placed in their own data block or the entire data block should be modified.

• Method Execution Control Method. If the Data Block GUID Mapping control method describes a data block that does have the WMIACPI_REG_METHOD flag set, there needs to be a control method that performs the action required of the method.

  By convention, the name of the control method is WM xx, where xx is the 2-character ID that maps to the GUID. This method call has three parameters; the first is a ULONG that has the instance index being executed; the second contains the method ID for the method being executed; and the third is a buffer that contains the input for the method call. If the GUID for the WMI method is registered with the WMIACPI_REGFLAG_STRING flag, then the mapper assumes that buffer passed in is a string. The mapper will convert the incoming string from UNICODE to ASCIZ. If the result of the WMxx control method is a string, the mapper will convert the result string from ASCIZ to UNICODE. The return value of the WMxx method should be a buffer with the result of the method call.This control method is required for those data blocks specified in the Data Block GUID Mapping array that have the WMIACPI_REG_METHOD flag set. Because the mapper is unaware of the format of the data block passed by the caller of the WMI method, it will pass the buffer as a single buffer parameter to the WMxx control method. The control method can use the ASL instructions CreateBitField, CreateDWordField, CreateField, and CreateWordFieldto break the buffer into its parts.

• Event Enable and Disable Control Method. For each event specified in the Event GUID Mapping control method that has the WMIACPI_REG_EXPENSIVE flag set, there needs to be a control method that is invoked whenever launching of the event should be enabled and disabled.

  By convention, the control method is named WExx, where xx is the hex value of the notification code passed by the event handler control method. This method has one parameter, a UCHAR that has a value of 0 if the event is to be disabled or a nonzero value if it is to be enabled. This method is optional and should only be supported if keeping the event enabled incurs significant overhead.

• Data Collection Enable and Disable Control Method. For each data block described in the Data Block GUID Mapping control method that has the WMIACPI_REG_EXPENSIVE flag set, there needs to be a control method that is invoked whenever collection of the data that composes the data block should be enabled and disabled.

  By convention, the control method is named WC xx, where xx is the 2-character ID that maps to the GUID. This method has one parameter, a UCHAR that has a value of 0 if data block collection is to be disabled or a nonzero value if it is to be enabled. This method is optional and should only be supported if collecting the data for the data block incurs significant overhead.

• Additional Event Data. The _WED control method is evaluated by the mapper in response to receiving a notification from a control method. The results of the evaluation are passed as part of the WMI event information. This mechanism allows additional data to be included with an event.

  The control method takes one parameter, which is the notification code that caused the notification to occur. If the result of the _WED control method is a string, then the string is converted from ASCIZ to UNICODE before launching the WMI event.

Data Block Design for Windows Instrumentation

Design Considerations. Consider the following in designing data blocks for instrumentation under Windows 2000/Windows XP:

• Data items that are read-only and are commonly used together should be combined into a single data block.

• Data items that are strings must be segregated into their own data block and registered with the WMIACPI_REGFLAG_STRING flag set so that the mapper can convert between ASCIZ and UNICODE.

• Data items that can be set individually should be segregated into their own data blocks. For example, a set of data items that must be set all at the same time can be combined into a single data block.

MOF Data Types. The Managed Object Format (MOF) for the data blocks implemented can be supplied as either a resource attached to a file or as the buffer that results from the evaluation of a control method. To establish the former, either bind the resource to the Wmiacpi.sys image or establish a REG_EXPAND_SZ registry value named MofImagePath under the WMIACPI service key. The contents of the value is a path to the image file that contains the resource. In either case, the resource must be named MofResourceName.

The buffer resulting from the evaluation of the WQxx control method assigned to the binary MOF GUID describes all data blocks, WMI methods, and events for the device in a compressed binary format. This binary data is created by building a text file using the MOF language and compiling it with the MOF compiler.

MOF data types are very rich. MOF supports the basic data types of 8-, 16-, 32-, and 64-bit signed and unsigned integers, Boolean terms, floating points, strings, and UTC datetimes. Embedded classes--that is, structures that can contain basic data types and other embedded classes--are also supported. In addition, fixed and variable length arrays of basic data types and embedded classes are supported.

The MOF language defines the data types shown in the following table.

MOF Data Types

**Important:**Because the MOF data types are much richer than those for ACPI control methods, the control method must be careful to pack the data blocks correctly within an ACPI buffer. The control method can also restrict itself to using only common data types.

Each MOF class represents a data block and may contain one or more properties that represent data items within the data block. A MOF class would hold all information needed to parse a data block returned from the mapper. In addition, the MOF language allows rich meta-data to be included as qualifiers on properties and classes. Some qualifiers are required, but most are optional.

Class and data item qualifiers are defined in the following table.

Class and Data Item Qualifiers

The order that the data items are laid out in the data block is controlled by the data item ID. Data item IDs must be allocated contiguously starting with data item ID 1. The data item order specified in the MOF is not relevant.

MOF supports arrays of the basic types shown in the "MOF Data Types" table shown earlier. A variable sized array must have a **WmiSizeIs()**qualifier that specifies the property that has the number of elements in the array.

Data Block Format. The format of the data block buffer returned from the query control method and passed into the set control method must be consistent with the description of it specified by the MOF for that data block with respect to the order and size of the data items within the data block. The Boolean data type is 1 byte in length and has a value of 0 for FALSE and non-zero value for TRUE. The string data type is a C-style ANSI null-terminated string.

Standard Data Blocks, Methods, and Events. Additional data blocks, events, and methods will be defined in the future; they should be implemented by all OEMs in order to ensure a minimum of functionality on all PCs. In the future, an industry standard will be defined for the globally unique GUIDs to be assigned to the data blocks. The WMI component within Windows will contain the MOF definition for these standard data blocks so it does not need to be part of the result from the binary MOF query.

Custom Data Blocks, Methods and Events. Custom or OEM-specific data blocks, events, and methods can be added by including them in the result of the _WDG method. The GUIDs that are assigned must be globally unique so they can be generated by a tool such as Guidgen or Uuidgen, which are provided with the WMI information in the Microsoft Platform SDK.

The MOF definition for these custom data blocks must be included in the results of the WQxx method, where xx has been mapped to the MOF Data GUID, which is the GUID that is queried and returns MOF data--in order for applications to be able to access the data blocks. Or the MOF could be added as a resource to Wmiacpi.sys with a name of MofResourceName and a type MOFDATA. It can also be a resource in another image file with same name and type that is pointed to by the MofImagePath value in the registry key HKLM\CurrentControlSet\Services\WmiAcpi.

FAQ about WMI and ACPI for Windows Instrumentation

How does WMI find ACPI/ASL code?

In ASL, the developer creates a device with an _HID of PNP0c14. The operating system enumerates the device and loads the Wmiacpi.sys driver on top of it.

How does the MOF associated with ACPI BIOS get registered?

It is either a resource attached to Wmiacpi.sys or another image file such as a resource-only DLL.

How does a management application discover the classes and properties provided by ASL instrumentation?

By looking in the WMI namespace of the schema.

Is the following true? Because very few ACPI standards exist for instrumentation, most of the ACPI instrumented features will appear differently on each vendor's product, and management applications will have to be "taught" to interpret the varying classes and methods.

Microsoft is looking at standardizing this. Any suggestions are appreciated.

Who provides the MOF files for standard ACPI features such as thermal monitoring?

Windows 2000/Windows XP has a MOF file for thermal zone temperature as part of the operating system and instruments it within Acpi.sys, outside of the mapper.

Typically, MOF files are compiled into BMF files and attached to a driver as a resource. The BMF files can be in the ROM or on disk. WMI determines the location of the MOF information by looking at the registry for the MofImagePath value under the WMIACPI service. If this does not exist, then WMI looks at the ImagePath value. If Wmiacpi.sys does not have a MOF resource, then WMI will query the binary MOF GUID for the MOF information.A driver may have a static list of pre-built MOF files; if so, it can "dynamically" report one of them. The mechanism is to report the file using a predefined GUID that returns a binary MOF.To dynamically build a MOF file, a driver would have to build a MOF file and then launch the MOF compiler, which is difficult. Currently, to do this on the machine running Wmiacpi.sys, the mofcomp command can be used to load the MOF file directly into the CIMOM database.

ASL Methods and Sample Code

The following list represents some of the ASL methods defined by the ACPI specification. These methods are of particular interest for systems management. None of these methods have been implemented within the WMI/ACPI mapper to date. A BIOS developer, for example, could use these methods to expose data using the mapper. These methods represent good opportunities for OEMs to differentiate their products with minimal effort:

• _ACX - Temperature threshold at which various degrees of active cooling are engaged

• _CRT - Critical temperature at which system will shut down

• _PSV - Temperature at which system will throttle CPU in order to cool system

• _LID - Status of the lid (open or closed)

• _PSR- Whether the machine running on AC

The same applies for these method for Control Method Battery devices:

• _BIF - Battery information such as model, serial number, design capacity, last full charge capacity, technology, and battery capacity

• _BST - Battery state, battery present rate, battery remaining capacity, and battery voltage present

ASL Sample Code for an Event and Initiating Method

The following ASL code implements an event and a method that can be called to initiate that event.

Device(AMW0)
{
   // pnp0c14 is Plug and Play ID assigned to WMI mapper
   Name(_HID, "pnp0c14")
   Name(_UID, 0x0)

   //
   // Description of data and events supported
   Name(_WDG, Buffer() {
       0x6a, 0x0f, 0xBC, 0xAB, 0xa1, 0x8e, 0xd1, 0x11, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10, 0, 0,
        66, 65,        // Object ID (BA)
        3,             // Instance Count
        0x01,          // Flags (WMIACPI_REGFLAG_EXPENSIVE)
       0x6b, 0x0f, 0xBC, 0xAB, 0xa1, 0x8e, 0xd1, 0x11, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10, 0, 0,
        66, 66,        // Object ID (BB)
        3,             // Instance Count
        0x02,          // Flags (WMIACPI_REGFLAG_METHOD)
       0x6c, 0x0f, 0xBC, 0xAB, 0xa1, 0x8e, 0xd1, 0x11, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10, 0, 0,
        0xb0, 0,       // Notification ID
                    1,             // Instance Count
        0x08           // Flags (WMIACPI_REGFLAG_EVENT)
    })

    //
    // Storage for the 3 instances of BA
    Name(STB0, Buffer(0x10) { 
        1,0,0,0, 2,0,0,0, 3,0,0,0, 4,0,0,0
         })
    Name(STB1, Buffer(0x10) {
        0,1,0,0, 0,2,0,0, 0,3,0,0, 0,4,0,0
         })
    Name(STB2, Buffer(0x10) {
        0,0,1,0, 0,0,2,0, 0,0,3,0, 0,0,4,0
         })

    //
    // Query data block
    // Arg0 has the instance being queried
    Method(WQBA, 1) {
        if (LEqual(Arg0, 0)) {
            Return(STB0)
        }
        if (LEqual(Arg0, 1)) {
            Return(STB1)
        }
        if (LEqual(Arg0, 2)) {
            Return(STB2)
        }
    }

    //
    // Set Data Block
    // Arg0 has the instance being queried
    // Arg1 has the new value for the data block instance
    Method(WSBA, 2) {
        if (LEqual(Arg0, 0)) {
            Store(Arg1, STB0)
        }
        if (LEqual(Arg0, 1)) {
            Store(Arg1, STB1)
        }
        if (LEqual(Arg0, 2)) {
            Store(Arg1, STB2)
        }
    }
    //
    // Storage for data block BB
    Name(B0ED, Buffer(0x10) { 
        0,0,0,1, 0,0,0,2, 0,0,0,3, 0,0,0,4
         })

    //
    // Method Execution
    // Arg0 is instance being queried
    // Arg1 is the method ID
    // Arg2 is the method data passed
    Method(WMBB, 3) {
        if (LEqual(Arg1, 1))
        {
            Store(Arg3, B0ED)
            Notify(AMW0, 0xB0)
            Return(Arg3)
        } else {
            Return(Arg1)
        }
    }

    //
    // More info about an event
    // Arg0 is the event ID that was launched ("fired")
    Method(_WED, 1) {
        if (LEqual(Arg0, 0xB0)) {
            Return(B0ED)
        }

    }
}

Sample ASL Code Embedding MOF Data in ASL

The following sample ASL code shows another example of implementing an event mechanism using ASL code. It also provides an example of embedding MOF data into ASL.

Device(AMW0)
{
//
// pnp0c14 is the ID assigned by Microsoft to the WMI to ACPI mapper
   Name(_HID, "pnp0c14")
   Name(_UID, 0x0)
//
// _WDG evaluates to a data structure that specifies the data blocks supported
// by the ACPI device.
   Name(_WDG, Buffer() {
       0x5a, 0x0f, 0xBC, 0xAB, 0xa1, 0x8e, 0xd1, 0x11, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10, 0, 0,
       65, 65,        // Object ID (AA)
       2,             // Instance Count
       0x01,          // Flags WMIACPI_REGFLAG_EXPENSIVE
       0x5b, 0x0f, 0xBC, 0xAB, 0xa1, 0x8e, 0xd1, 0x11, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10, 0, 0,
       65, 66,        // Object ID (AB)
       2,             // Instance Count
       0x02,          // Flags WMIACPI_REGFLAG_METHOD
       0x5c, 0x0f, 0xBC, 0xAB, 0xa1, 0x8e, 0xd1, 0x11, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10, 0, 0,
       0xa0, 0,       // Notification ID
       1,             // Instance Count
       0x08,          // Flags (WMIACPI_REGFLAG_EVENT)

//
// This GUID for returning the MOF data
       0x21, 0x12, 0x90, 0x05, 0x66, 0xd5, 0xd1, 0x11, 0xb2, 0xf0, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10,
       66, 65,        // Object ID (BA)
       1,             // Instance Count
       0x00,          // Flags
   })

//
// Collection control method. If Arg0 is not zero then collection for the
// data block is enabled. If Arg0 is zero then collection is disabled. If 
// this method does not exist then it is assumed that collection control is
// not required. Collection control is only useful when collection of the 
// data block causes overhead.
   Method(WCAA, 1) {
       if (LEqual(Arg0, Zero)) {
           // Disable collection of data
       } else {
           // Enable collection of data
       }
   }

//
// Query method for data block AA. Arg0 has the data block instance index
   Method(WQAA, 1) {
       if (LEqual(Arg0, Zero)) {
           // Query is for first instance of data block
           return(0x10)
       } else {
           // Query is for second instance of data block
           return(0x20)
       }
   }

//
// Set method for data block AA. If data block is read-only then this method
// does not need to exist. Arg0 has the instance index of the data block,
// Arg1 has the new value for the data block.
   Method(WSAA, 2) {
       if (LEqual(Arg0, Zero)) {
           // Set is for first instance of data block
       } else {
           // Set is for second instance of data block
       }
   }

//
// Event enable/disable method. If event does not need to be armed/disarmed
// then this method is not needed. Arg0 is Zero if event is being disarmed or
// non zero if event is being armed.
   Name(ACEN, 0)
   Method(WEA0, 1) {
       Store(Arg0, ACEN)
   }

//
// _WED is called in response to an event launching ("firing") to gain additional 
// information about the event. Arg0 has the NotifyId for the event launched.
   Method(_WED, 1) {
       if (LEqual(Arg0, 0xA0)) {
           Return(0x100)
       }
   }

//
// Evaluation of this method causes the event 0xA0 to be fired. Since it is
// defined by the _WDG method it is callable via WMI. Arg0 has the instance
// index and Arg1 has any input parameters.
   Method(WMAB, 3) {
       //
       // If event was armed then launch it
       if (LEqual(ACEN, 1)) {
           Notify(AMW0, 0xa0)
       }
       Return(Arg1)
   }
   Name(WQBA, Buffer(926) {
    0x46, 0x4f, 0x4d, 0x42, 0x01, 0x00, 0x00, 0x00, 0x8e, 0x03, 0x00, 0x00, 0xf6, 0x0f, 0x00, 0x00,
    0x44, 0x53, 0x00, 0x01, 0x1a, 0x7d, 0xda, 0x54, 0x98, 0xdd, 0x87, 0x00, 0x01, 0x06, 0x18, 0x42,
    0x10, 0x0b, 0x10, 0x0a, 0x0b, 0x21, 0x02, 0xcb, 0x82, 0x50, 0x3c, 0x18, 0x14, 0xa0, 0x25, 0x41,
    0xc8, 0x05, 0x14, 0x55, 0x02, 0x21, 0xc3, 0x02, 0x14, 0x0b, 0x70, 0x2e, 0x40, 0xba, 0x00, 0xe5,
    0x28, 0x72, 0x0c, 0x22, 0x82, 0xfd, 0xfb, 0x07, 0xc1, 0x90, 0x02, 0x08, 0x29, 0x84, 0x90, 0x08,
    0x58, 0x2a, 0x04, 0x8d, 0x10, 0xf4, 0x2b, 0x00, 0xa1, 0x43, 0x01, 0x32, 0x05, 0x18, 0x14, 0xe0,
    0x14, 0x41, 0x04, 0x41, 0x62, 0x17, 0x2e, 0xc0, 0x34, 0x8c, 0x06, 0xd0, 0x36, 0x8a, 0x64, 0x0b,
    0xb0, 0x0c, 0x2e, 0x98, 0xa3, 0x08, 0x92, 0xa0, 0xc6, 0x09, 0xa0, 0xc4, 0x4c, 0x00, 0xa5, 0x13,
    0x5c, 0x36, 0x05, 0x58, 0xc4, 0x96, 0x50, 0x14, 0x0d, 0x22, 0x4a, 0x82, 0x13, 0xea, 0x1b, 0x41,
    0x13, 0x2a, 0x57, 0x80, 0x64, 0x78, 0x69, 0x1e, 0x81, 0xac, 0xcf, 0x41, 0x93, 0xf2, 0x04, 0xb8,
    0x9a, 0x05, 0x7a, 0x8c, 0x34, 0xff, 0x30, 0x41, 0x99, 0x14, 0x43, 0x0e, 0x20, 0x24, 0x71, 0x98,
    0xa0, 0x9d, 0x59, 0xed, 0x18, 0xd2, 0x3d, 0x07, 0x32, 0x4d, 0x60, 0x21, 0x70, 0x9e, 0xb8, 0x19,
    0xa0, 0xf0, 0x5b, 0x1d, 0x80, 0xe0, 0x2b, 0x1d, 0x15, 0xd2, 0xeb, 0x34, 0x64, 0x72, 0x46, 0x48,
    0xf8, 0xff, 0x7f, 0x02, 0x26, 0xe3, 0xb7, 0x60, 0x02, 0xa5, 0xd9, 0xb2, 0x82, 0x4b, 0x80, 0xc1,
    0x68, 0x00, 0x91, 0xa2, 0x69, 0xa3, 0xe6, 0xea, 0xf9, 0x36, 0x8f, 0xaf, 0x59, 0x7a, 0x9e, 0x47,
    0x7a, 0x34, 0x56, 0x36, 0x05, 0xd4, 0xf8, 0x3d, 0x9d, 0x93, 0xf3, 0x4c, 0x02, 0x1e, 0x9c, 0x61,
    0x4e, 0x87, 0x83, 0xf1, 0xb1, 0xb1, 0x51, 0x70, 0x74, 0x03, 0xb2, 0x31, 0x38, 0xc6, 0xb0, 0xd1,
    0x73, 0x39, 0x81, 0x47, 0x82, 0x43, 0x89, 0x7e, 0x0e, 0x6f, 0x00, 0x47, 0x17, 0xe3, 0x04, 0xce,
    0x27, 0xc1, 0x61, 0x06, 0x39, 0xe3, 0x33, 0xf4, 0x44, 0x2c, 0x68, 0xd6, 0x02, 0x0a, 0x62, 0xa4,
    0x58, 0xa7, 0xf5, 0x7c, 0x10, 0x8b, 0x41, 0x05, 0x8b, 0x11, 0xdb, 0x50, 0x87, 0x60, 0x18, 0x8b,
    0x46, 0x11, 0xc8, 0x49, 0x3c, 0x49, 0x30, 0x94, 0x40, 0x51, 0x0c, 0x12, 0xda, 0xc3, 0x36, 0x92,
    0x81, 0xcf, 0xdb, 0x20, 0xc7, 0x84, 0x51, 0x01, 0x21, 0xcf, 0xe3, 0xd0, 0x28, 0x4d, 0xd0, 0xfd,
    0x29, 0x40, 0x37, 0x8b, 0x08, 0x67, 0x54, 0xd8, 0x44, 0x64, 0x6d, 0x02, 0xb2, 0x25, 0x40, 0x1c,
    0xbe, 0x40, 0x1a, 0x43, 0x11, 0x44, 0x84, 0x98, 0x51, 0x8c, 0x19, 0x30, 0x82, 0x51, 0x0e, 0xa6,
    0x39, 0x10, 0x69, 0x13, 0x30, 0xf6, 0x20, 0xd1, 0x62, 0x31, 0x04, 0xdb, 0x9f, 0x83, 0x30, 0x0e,
    0x05, 0xa3, 0x03, 0x42, 0xe7, 0x84, 0xc3, 0x3b, 0x30, 0x9f, 0x1e, 0x4c, 0x70, 0xda, 0xcf, 0x07,
    0xaf, 0x0b, 0x21, 0x8b, 0x17, 0x20, 0x0d, 0x43, 0xf8, 0x09, 0x6a, 0x7d, 0x51, 0xe8, 0x5a, 0xe0,
    0x34, 0xe0, 0xa8, 0xeb, 0x82, 0x6f, 0x01, 0xbe, 0x01, 0x9c, 0xe0, 0xe3, 0x85, 0xf1, 0x83, 0x1c,
    0xc1, 0x01, 0x3c, 0x44, 0xbc, 0x1a, 0x78, 0x08, 0x9e, 0xc3, 0xfb, 0x05, 0x3b, 0x0f, 0x60, 0xff,
    0xff, 0x04, 0x5d, 0xe3, 0xe9, 0x92, 0x70, 0x02, 0x96, 0x83, 0x86, 0x1a, 0xac, 0x2f, 0x00, 0x27,
    0xe9, 0xc1, 0x1a, 0xae, 0xae, 0xd3, 0x06, 0x7a, 0xba, 0xa7, 0x72, 0x5a, 0xa5, 0x0a, 0x30, 0x7b,
    0x94, 0x20, 0x04, 0xcf, 0x1e, 0x6c, 0xde, 0x67, 0x73, 0xe6, 0x09, 0x9e, 0x14, 0x3c, 0x05, 0x3e,
    0x2d, 0xcf, 0xd2, 0x97, 0x0e, 0x5f, 0x09, 0x7c, 0x9f, 0x30, 0x41, 0xf4, 0x27, 0x17, 0x36, 0x1a,
    0xb8, 0xc3, 0xc6, 0x8d, 0x06, 0xce, 0xe5, 0xe0, 0xb1, 0xc3, 0x33, 0xf7, 0x5c, 0x4d, 0x50, 0xf3,
    0xe5, 0x42, 0x4e, 0x66, 0x83, 0xd2, 0x03, 0xa2, 0x01, 0x3f, 0x34, 0x60, 0xd0, 0x1f, 0x19, 0xb8,
    0xc8, 0x8b, 0x02, 0x95, 0x86, 0xac, 0xbf, 0x86, 0x45, 0x8d, 0x9b, 0x12, 0x58, 0xca, 0xa1, 0x82,
    0xdc, 0x33, 0x7c, 0x9e, 0x38, 0x8c, 0x57, 0x00, 0xcf, 0xe6, 0xa0, 0x7c, 0x73, 0x71, 0xba, 0x7b,
    0x05, 0x68, 0x66, 0x83, 0xbb, 0x51, 0x80, 0x05, 0xc3, 0xd7, 0x03, 0xdf, 0x30, 0xd8, 0xf1, 0xc3,
    0xd7, 0x0c, 0x36, 0x24, 0x83, 0x45, 0x89, 0x14, 0x9b, 0x4d, 0xca, 0x03, 0xc0, 0xe0, 0xbd, 0xd7,
    0xf8, 0x70, 0x61, 0x48, 0x9f, 0x31, 0xe0, 0x1e, 0x05, 0xe0, 0xfd, 0xff, 0xcf, 0x09, 0xe0, 0xb8,
    0x6d, 0xf8, 0x2a, 0x62, 0x67, 0xf7, 0x0b, 0x5d, 0x6f, 0xb0, 0xf7, 0x1d, 0x78, 0xf8, 0x87, 0x85,
    0xbb, 0x0b, 0x30, 0xb0, 0x13, 0xc5, 0x1c, 0x78, 0x80, 0xc7, 0x64, 0x1e, 0x78, 0xc0, 0x75, 0x96,
    0x82, 0x3d, 0x04, 0xae, 0xfa, 0xc0, 0x83, 0xca, 0xf1, 0x6a, 0xa0, 0x67, 0x1e, 0xc0, 0xec, 0xff,
    0xff, 0xcc, 0x03, 0x8c, 0xe0, 0x9f, 0x79, 0x80, 0x6b, 0xf4, 0x6b, 0x81, 0xde, 0x57, 0x3e, 0xf3,
    0x00, 0x7c, 0x50, 0x79, 0x33, 0x01, 0xcd, 0xff, 0xff, 0x66, 0x02, 0xe3, 0xe0, 0xe0, 0x83, 0x88,
    0xaf, 0x32, 0x3e, 0x11, 0x02, 0x93, 0xab, 0x09, 0x70, 0x09, 0x79, 0x27, 0xa2, 0x01, 0x07, 0x41,
    0xaf, 0x01, 0x5c, 0x0b, 0x88, 0x66, 0xc8, 0xa6, 0x89, 0x25, 0x98, 0xe5, 0x22, 0x40, 0xef, 0x8a,
    0x3e, 0x2a, 0xf1, 0x31, 0xfa, 0xa8, 0xc4, 0x70, 0xdf, 0x85, 0x8c, 0x7b, 0x7a, 0x67, 0xf7, 0xac,
    0x84, 0xb9, 0x04, 0xbc, 0x8f, 0x80, 0x65, 0xf2, 0xf8, 0xd3, 0x07, 0x47, 0xf4, 0x85, 0xc1, 0x77,
    0x23, 0x78, 0x04, 0xd5, 0x5f, 0x65, 0xa8, 0xfe, 0xbd, 0x48, 0x2f, 0x0c, 0xea, 0x2a, 0x03, 0x5c,
    0xff, 0xff, 0x57, 0x19, 0x36, 0xc8, 0x63, 0x05, 0xcb, 0xf9, 0x11, 0x33, 0xc7, 0xd3, 0x8c, 0xe2,
    0xa9, 0x78, 0xb8, 0xec, 0x62, 0x65, 0xef, 0x53, 0x25, 0xc7, 0x17, 0x5f, 0xab, 0xf0, 0x20, 0x8f,
    0x31, 0xbe, 0xc3, 0x80, 0x71, 0x04, 0xef, 0x30, 0xc0, 0x35, 0xf0, 0xcb, 0x41, 0xd7, 0x40, 0xc0,
    0xf6, 0xff, 0xff, 0x0e, 0x03, 0x96, 0xe0, 0x10, 0xba, 0x06, 0xe2, 0x64, 0x1c, 0x5b, 0xc8, 0x4d,
    0xca, 0x53, 0x36, 0xc1, 0xa0, 0x13, 0xa6, 0x47, 0x40, 0xf0, 0xdc, 0x2b, 0x7c, 0x98, 0x00, 0xc7,
    0x48, 0x30, 0xe7, 0x08, 0x9f, 0x1f, 0x7c, 0x7d, 0x78, 0x93, 0x60, 0x37, 0x0e, 0xc3, 0xf8, 0xca,
    0x07, 0x0f, 0xf2, 0x15, 0x8b, 0x5d, 0x26, 0xf8, 0x49, 0x0f, 0x6c, 0x17, 0x65, 0x70, 0xdc, 0x7f,
    0xe0, 0x5c, 0x94, 0x81, 0x11, 0xee, 0xe3, 0x0f, 0xf8, 0x0f, 0xcb, 0x70, 0xfe, 0xff
           })
        }

Sample MOF File

This sample MOF file complements the previous ASL code.

[abstract]
class AcpiSampleBase
{
};

[abstract]
class AcpiSampleEvent : WMIEvent
{
};

[Dynamic, Provider("WMIProv"),
 WMI,
 Description("Counter for number of times the case has been hit"),
 GUID("{ABBC0f5a-8ea1-11d1-A000-c90629100000}"),
 locale("MS\\0x409")]
class MachineHitSensor : AcpiSampleBase
{
    [key, read]
     string InstanceName;
    [read] Boolean Active;

    [WmiDataId(1),
     Description("Number of times the case sensor determined that the machine has been hit"),
     read
    ] uint32 NumberTimesHit;
};

[Dynamic, Provider("WMIProv"),
 WMI,
 Description("Counter for number of times the case has been hit"),
 GUID("{ABBC0f5b-8ea1-11d1-A000-c90629100000}"),
 locale("MS\\0x409")]
class MachineHitSimulate : AcpiSampleBase
{
    [key, read]
     string InstanceName;
    [read] Boolean Active;

    [WmiMethodId(1),
     Description("Simulate hitting the machine")
    ] void HitMachine();
};

[Dynamic, Provider("WMIProv"),
 WMI,
 Description("Event generated when machine is hit"),
 GUID("{ABBC0f5c-8ea1-11d1-A000-c90629100000}"),
 locale("MS\\0x409")]
class MachineHitEvent : AcpiSampleEvent
{
    [key, read]
     string InstanceName;
    [read] Boolean Active;

    [WmiDataId(1),
     Description("Force with which the machine was hit")
    ] uint32 Force;
};

Appendix C--ASL sample code

Device(WMI1) {
    Name (_HID, EISAID("PNP0Cxx"))        // Plug and Play ID for mapping driver 
    _UID(1)

    //
    // Data block and Wmi method to Object ID mappings
    Name(_WDG, Buffer() {
          // Object AA - {ABBC0F5A-8EA1-11d1-A53F-00A0C9062910}
              0xABBC0F5A, 0x8ea1, 0x11d1, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10,
              `A','A',       // Object ID
               1,            // Instance Count
               0x04,         // Flags (WMIACPI_REGFLAG_STRING)
    
          // Object AB - {ABBC0F5B-8EA1-11d1-A53F-00A0C9062910}
              0xABBC0F5B, 0x8ea1, 0x11d1, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10,
              `A','B',    // Object ID
              2,          // Instance Count
              0x01,       // Flag (WMIACPI_REGFLAG_EXPENSIVE)

          // Object AC - {ABBC0F5C-8EA1-11d1-A53F-00A0C9062910}
              0xABBC0F5C, 0x8ea1, 0x11d1, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10,
              `A','C',    // Object ID
              1,          // Instance Count
              0x06,       // Flag (WMIACPI_REGFLAG_METHOD | _STRING)

          // Event 0x80 - {ABBC0F5D-8EA1-11d1-A53F-00A0C9062910}
              0xABBC0F5D, 0x8ea1, 0x11d1, 0x00, 0xa0, 0xc9, 0x06, 0x29, 0x10,
              0x80,        // Notification value
              0,           // Reserved
              0,           // Instance Count (Not meaningful for events)
              0x0D         // Flags (WMIACPI_REGFLAG_EXPENSIVE | _STRING |_EVENT)
    })



    //
    // IO ports for configuration of Object AB
    OperationRegion(CAB0, SystemIo, 0xf8, 1)   // Instance 0
    OperationRegion(CAB1, SystemIo, 0xfc, 1)   // Instance 1
    OperationRegion(CABC, SystemIo, 0xf4, 1)   // Enable/Disable Collection

    Method(WQAB, 1) {
        //
        // Read value from IO space for instance
        if (LEqual(Arg0, Zero) {
            Store(CAB0, Local0)
        } else {
            Store(CAB1, Local0)
        }

        //
        // If any of the lower 3 bits are set then return TRUE, else FALSE
        if (And(Local0, 7))
            Return( 0x00000001 )
        } else {
            Return( 0x00000000 )
        }
    }

    //
    // Set the values for object AB
    Method(WSAB, 2) {
        if (LEqual(Arg0, Zero) {
                // Change contents of first instance of data block to 
                // values in buffer in Arg1
            } else {
               // Change contents of second instance of data block to 
               // values in buffer in Arg1
            }
       }

    //
    // Collection notification for object AB
    Method(WCAB, 1) {
        if (LEqual(Arg0, 1)
        {
            Store(One, CABC)     // If enable, write all 1's to port
        } else {
            Store(Zero, CABC)    // If disable, write all 0's to port
        }
    }



    //
    // Storage for maintaining values for the AA method. 
    Name(STAA, "XYZZY")

    Method(WQAA, 1) {
        //
        // Only one instance for AA so no need to check arg
        return(STAA);
    }


    // Data block mapped to Object AA does not support set so it does not need
    // a WSAA method

    //
    // Storage for maintaining state of flag that determines whether to fire (launch)
    // the event or not. By default firing is disabled
    Name(FIRE, 0)

    //
    // This method will reset the values for AA and send a notification of
    // its occurrence
    Method(WMAC, 3) {
        Store(STAA, Local0)
        Store("XYZZY", STAA)
        if (LEqual(FIRE, 1))
        {
            Notify(WMI1, 0x80)
        }
        Return(Local0)
    }

    //
    // Additional information about event
    Method(_WED) {
        return("Fired")
    }

    //
    // Event 0x80 Enable/Disable control method
    Method(WE80, 1) {
        Store(FIRE, Arg0)
    }
)

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