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USB Function Mass Storage Client Driver SCSI-2 Direct-Access Device Emulator (Windows Embedded CE 6.0)

  • Article

1/6/2010

The SCSI-2 direct-access device emulator abstracts a SCSI-2 direct-access device to the host and the transport. To execute a SCSI-2 command, the SCSI-2 direct-access device emulator provides the STORE_ExecuteCommand function, which the BOT_ExecuteCB and CBIT_ExecuteADSC functions wrap.

The following list shows what ptdData contains depending on whether ptcCommand represents a DATA_OUT or a DATA_IN transfer:

  • If the ptcCommand member represents a DATA_OUT transfer, then ptdData contains the data associated with the command.
  • If ptcCommand represents a DATA_IN transfer, then the ptdData member contains the data associated with the result of the command.

The following list shows the return values of STORE_ExecuteCommand depending on whether STORE_ExecuteCommand supports the command:

  • If the mass storage device supports and processes the command, then STORE_ExecuteCommand returns TRUE.
  • If the mass storage device does not support and process the command, the STORE_ExecuteCommand returns FALSE.
    The result of STORE_ExecuteCommand determines whether the command executed, and provides the transport with the ability to fail the command on the bus.

The USB mass storage class driver implements STORE_ExecuteCommand with a switch statement that includes a case statement for each supported SCSI-2 command. Not every SCSI-2 command corresponds to a block driver IOCTL. The emulator does not strictly translate commands; it also emulates commands. If there is not a corresponding block driver IOCTL for a particular SCSI-2 command, the SCSI-2 direct-access device emulator emulates the command.

The following table shows how the SCSI-2 direct-access device emulator handles two separate commands.

SCSI-2 command Result

TEST UNIT READY

To determine whether a block device can accept a medium-access command, the SCSI-2 direct-access device emulator determines whether the associated block driver is open.

READ(10)

To read data from the associated block device, the SCSI-2 direct-access device emulator builds a corresponding SG_REQ structure to apply to an IOCTL_DISK_READ invocation of DeviceIoControl.

To determine whether the mass storage device supports a particular SCSI-2 command, the SCSI-2 direct-access device emulator provides STORE_IsCommandSupported, which the BOT_HandleCBW and CBIT_HandleADSC functions wrap. STORE_IsCommandSupported accepts a SCSI-2 operation code and determines whether the SCSI-2 direct-access device emulator can support the command.

See Also

Concepts

USB Function Mass Storage Client Driver Development Concepts
USB Function Mass Storage Client Driver