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SpbCx Object Handles

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This topic describes object handles that are defined for the SPB framework extension (SpbCx) library.

Additionally, the SerCx2 DDI uses two of the generic object handle types, WDFDEVICE and WDFREQUEST, that are defined by the Kernel-Mode Driver Framework (KMDF). For more information about framework handle types, see Summary of Framework Objects.

This topic describes the following object handles:

Header: Spbcx.h

SPBREQUEST Object Handle

An SPBREQUEST object handle represents an I/O request that is issued to a target device on the bus.

DECLARE_HANDLE(SPBREQUEST)

The SPBREQUEST object class is derived from the WDFREQUEST object class, which represents an I/O request that is dispatched by the I/O manager. Thus, WdfRequestXxx methods that take WDFREQUEST handle values as parameters accept SPBREQUEST handle values as valid parameter values. For more information about these methods, see Framework Request Objects.

However, some SpbCx methods and callback functions specifically require SPBREQUEST handles as parameters. For such a parameter, substituting a WDFREQUEST handle that is not also an SPBREQUEST handle is an error.

For example, the SpbRequestGetTransferParameters method takes an SPBREQUEST handle as a parameter. To supply, for this parameter, a WDFREQUEST handle that is not also an SPBREQUEST handle is an error. The reason for this requirement is that an SPBREQUEST object must store additional, SPB-specific state information to support I/O transfer sequences. The WDFREQUEST base object class does not provide this support.

During device initialization, your SPB controller driver can assign a per-request context to an SPBREQUEST handle by calling the SpbControllerSetRequestAttributes method.

SPBTARGET Object Handle

An SPBTARGET object handle identifies a logical connection from a client (peripheral driver) to an addressable port or peripheral device on the bus.

DECLARE_HANDLE(SPBTARGET)

For an I2C bus, an SPBTARGET handle corresponds to a specific device address.
For an SPI bus, an SPBTARGET handle corresponds to a device-select line.

Typically, an SPBTARGET object exists from the start of the EvtSpbTargetConnect event callback through the end of the corresponding EvtSpbTargetDisconnect event callback. However, the lifetime of the SPBTARGET object might extend beyond the second callback if the SPB controller driver takes an additional reference on the SPBTARGET object to prevent the object from unexpectedly disappearing during the processing of an I/O request for the target.

The SPB controller driver performs all hardware-specific operations for an SPB controller device. When a client sends an IRP_MJ_CREATE request to open a connection to a target on the bus, the SPB framework extension (SpbCx), which manages the I/O queue for the controller driver, passes this request to the SPB controller driver by calling this driver's EvtSpbTargetConnect callback function. This Target parameter of this function is an SPBTARGET handle. The function can use this handle to retrieve connection-specific resource information (for example, the device address) from the PnP manager. When the client sends an IRP_MJ_CLOSE request to close the connection, SpbCx passes this request to the SPB controller driver's EvtSpbTargetDisconnect callback function, which releases these resources.

Exclusive-Mode Access

Clients have exclusive-mode to access target devices. Only one client can have a connection to a particular target device at a time. SpbCx ensures that only one SPBTARGET handle exists for a target device address on the bus. This restriction is necessary because SpbCx does not support the interleaving of I/O requests that are sent by two or more clients to a target device. If a target device must be able to receive requests from several clients, this device requires a MUX driver—separate from the controller driver—that can properly interleave the requested operations.

Interoperability with KMDF

The SerCx2 Driver Support Methods and SpbCx Event Callback Functions that are defined by SpbCx use SPBTARGET handles to represent open connections to target devices on the bus. However, a controller driver must typically call KMDF methods that require WDFFILEOBJECT handles, instead of SPBTARGET handles, to designate target devices.

An SPBTARGET object is similar to a WDFFILEOBJECT object. However, an SPBTARGET object contains additional, SPB-specific information. For example, during the processing of an IOCTL_SPB_EXECUTE_SEQUENCE I/O control request, the SPBTARGET object for the target device tracks the state of the transfers in the I/O transfer sequence.

To obtain the WDFFILEOBJECT handle to a target, the SPB controller driver calls the SpbTargetGetFileObject method. This method accepts, as an input parameter, an SPBTARGET handle to an open target device, and returns the corresponding WDFFILEOBJECT handle to this target.

In accordance with KMDF conventions, the SPB controller driver can attach its own context to the SPBTARGET object for a target device, and this context can include associated EvtCleanupCallback and EvtDestroyCallback callback functions. The SPB controller driver uses this context to track information that is specific to the controller driver and to the target device. In addition, this driver can create child objects of the SPBTARGET object, such as timers, DPCs, or, if needed, I/O requests and I/O queues.