Hitachi HUS151473VL3800 Specifications - Page 178

17.17.3 Descriptor (Mode 00011b) In this mode, a maximum of four bytes of READ BUFFER descriptor information are returned. The drive returns the descriptor information for the buffer specified by the Buffer ID. • Buffer ID field should normally be set to zero, indicating the drive data transfer buffer. If any other value is specified, the drive returns all zeros in the READ BUFFER descriptor. • Buffer Offset field is reserved. • Allocation Length should be set to four or greater. The drive transfers the allocation length or four bytes of READ BUFFER descriptor, whichever is less. The allocation length of zero indicates no data is transfered.The allocation length of greater than zero and less than four (size of the Descriptor) is an invalid request and will cause the command to be terminated with Check Condition status. The drive shall set sense key to Illegal Request and additional sense code to Illegal Field in CDB. The READ BUFFER descriptor is defined in the figure below. Table 112: Read Buffer Description Bit Byte 7 6 5 4 3 2 1 0 Offset Boundary = 0x09 (MSB) 1-3 Buffer Capacity (LSB) The value contained in the Buffer Offset field of subsequent WRITE BUFFER and READ BUFFER commands should be a multiple of two to the power of the offset boundary. The offset boundary is always set to nine, which indicates Sector Boundaries. Hitachi Confidential Hitachi Ultrastar 15K147 SCSI Hard Disk Drive Specification 160