Opening, Initializing and Closing an SD Card Bus Interface

Secure Digital (SD) device drivers must open and initialize an SD bus interface to interact with the devices they manage or the host controller. This requires two calls to the SD bus library: a call to SdBusOpenInterface followed by a call to a routine supplied by the bus driver that initializes the interface. SdBusOpenInterface returns a pointer to the routine that initializes the interface in the InterfaceReference member of the SDBUS_INTERFACE_STANDARD structure. The device driver must call this initialization routine to supply the bus driver with a pointer to an interrupt notification callback routine. The bus driver uses this callback to notify the device driver of a hardware interrupt. For more information about the routine that initializes an SD bus interface, see PSDBUS_INITIALIZE_INTERFACE_ROUTINE. The device driver normally opens and initializes an SD bus interface from within its AddDevice routine.

The following code example illustrates the sequence of calls that open and initialize an SD bus interface:

  status = SdBusOpenInterface (pDevExt->UnderlyingPDO,

  if (NT_SUCCESS(status)) {
    SDBUS_INTERFACE_PARAMETERS interfaceParameters = {0};
    interfaceParameters.Size = 
    interfaceParameters.TargetObject = 
    interfaceParameters.DeviceGeneratesInterrupts = TRUE;
    interfaceParameters.CallbackRoutine = pMyDriverCallback;
    if (DeviceExtension->BusInterface.InitializeInterface) {
      status = (pDevExt->BusInterface.InitializeInterface)
        (pDevExt->BusInterface.Context, &interfaceParameters);

In this code example, the device driver calls SdBusOpenInterface to open the interface, and the bus driver stores a pointer to the initialization routine in the device extension (DeviceExtension->BusInterface.InitializeInterface). After SdBusOpenInterface returns, the driver retrieves this pointer from the device extension. Next, the driver puts a pointer to its own interrupt callback routine, pMyDriverCallback, in the SDBUS_INTERFACE_PARAMETERS structure and passes this structure to the initialization routine.

The device driver must also retrieve the context information that SdBusOpenInterface returns in the Context member of the SDBUS_INTERFACE_STANDARD structure. Whenever the driver calls an SD bus interface routine, it must pass in this context data.

Closing an SD Interface

To close an SD interface, drivers must dereference the interface by calling the routine in the InterfaceDereference member of the SDBUS_INTERFACE_STANDARD structure, which frees all resources allocated by the SdBusOpenInterface routine. SD device drivers should close all open SD interfaces when receiving any of the following IRPs:




The following code example illustrates how a driver can dereference an SD card bus interface:

if (pDevExt->BusInterface.InterfaceDereference) {
    (pDevExt->BusInterface.InterfaceDereference) (pDevExt->BusInterface.Context);
    RtlZeroMemory(&pDevExt->BusInterface, sizeof(SDBUS_INTERFACE_STANDARD));

The SdBusOpenInterface call stores a pointer to the interface dereference routine in the SDBUS_INTERFACE_STANDARD structure. However, drivers should verify that the pointer is not NULL before attempting to call the routine.