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SDCMD_DESCRIPTOR structure (sddef.h)

  • Article

The SDCMD_DESCRIPTOR structure defines a Secure Digital (SD) card command.

Syntax

typedef struct _SDCMD_DESCRIPTOR {
  SD_COMMAND_CODE       Cmd;
  SD_COMMAND_CLASS      CmdClass;
  SD_TRANSFER_DIRECTION TransferDirection;
  SD_TRANSFER_TYPE      TransferType;
  SD_RESPONSE_TYPE      ResponseType;
} SDCMD_DESCRIPTOR, *PSDCMD_DESCRIPTOR;

Members

Cmd

Contains a value of type SD_COMMAND_CODE that specifies the SD command. Cmd can be one of the following values.

Value Meaning
SDCMD_IO_RW_DIRECT Indicates a read or write operation of a single byte.
SDCMD_IO_RW_EXTENDED Indicates a read or write operation on a buffer in memory.

CmdClass

Contains an enumeration value of type SD_COMMAND_CLASS that specifies the class of the SD command.

TransferDirection

Contains an enumeration value of type SD_TRANSFER_DIRECTION that indicates the direction of the data transfer.

TransferType

Contains an enumeration value of type SD_TRANSFER_TYPE that indicates the type of the data transfer.

ResponseType

Contains an enumeration value of type SD_RESPONSE_TYPE that indicates the type of response that the card sends in response to the command indicated in the Cmd member.

Remarks

To send a command to an SD device, a device driver must complete the following steps:

  1. Set the RequestFunction member of SDBUS_REQUEST_PACKET to an SD_REQUEST_FUNCTION enumeration value of SDRF_DEVICE_COMMAND.

  2. Initialize the CmdDesc member of SDBUS_REQUEST_PACKET to define the command.

  3. Send the request to the bus driver by passing the initialized SDBUS_REQUEST_PACKET structure to either SdBusSubmitRequest or SdBusSubmitRequestAsync.

If a driver submits a command request without properly initializing the TransferDirection, TransferType, and ResponseType members of the command descriptor, the request will fail. These members cannot be 0.

Requirements

Requirement Value
Header sddef.h (include Sddef.h)

See also

SD_COMMAND_CLASS

SD_REQUEST_FUNCTION

SD_RESPONSE_TYPE

SD_TRANSFER_DIRECTION

SD_TRANSFER_TYPE

SdBusSubmitRequest

SdBusSubmitRequestAsync