Restrictions on SD Card Drivers
Certain restrictions apply to Secure Digital (SD) card device drivers that manage a function on an SD combo or multifunction card. The driver stacks for the various card functions on a multifunction card must operate independently of one another. To ensure this independence, the bus driver rejects the following operations:
SD commands that change the device state, such as SELECT_CARD.
SD I/O commands that specify function zero but are outside the range of the address specified in the function basic register (FBR).
SD I/O commands that specify a function number of a different device stack.
SD device drivers can manage the host controller's common register set and the state of the device by calling SdBusSubmitRequest with function requests of type SDRF_GET_PROPERTY and SDRF_SET_PROPERTY. For a description of these function request types, see SD_REQUEST_FUNCTION.