Information Technology Reference
In-Depth Information
Primary Commands
Each of the commands below is documented in the SCSI Primary Com-
mands (SPC) specification.
INQUIRY
The INQUIRY command requests a structure containing information
about the device. A device should be able to return the structure even when
the media isn't ready to respond to other commands. All SBC devices must
support the INQUIRY command.
The data returned by the device in the data-transport phase is at least 36
bytes (Table 6-3). The data identifies the peripheral device type (PDT) and
SPC version number and contains a vendor identification number, product
identification number, product revision number, and other information
about the device's abilities and supported protocols.
Table 6-4 lists common PDTs and their codes from the SCSI Primary Com-
mands document. Hard drives and flash-memory cards are type 00h:
direct-access block device. Devices with PDT = 0Eh use the reduced block
command (RBC) set, which is intended for block devices that have fewer
requirements and options compared to SBC devices. RBC might sound
appealing for some applications, but in practice the type is rarely used in
part because Windows doesn't provide a driver for it. If you need to provide
a vendor-specific RBC driver, you may as well define the device as vendor
specific in the descriptors. That way, you'll avoid confusion with any RBC
drivers a user may have loaded for another purpose.
As Chapter 3 explained, if the interface descriptor's bInterfaceSubClass
doesn't equal 06h (SCSI transparent command set), the PDT should match
the declared bInterfaceSubClass.
Note that the RMB parameter (bit 7 of byte 1) reports whether the device
has removable media. USB flash drives (thumb drives, pen drives, and simi-
lar devices) are removable devices with fixed media. However, some
Microsoft documentation recommends that flash drives declare that they
have removable media (RMB = 1), and many flash drives do so.
Search WWH ::
Custom Search