Sony AIT-SDX550 Product Specifications Manual page 96

6.Command Specification
DCC: A Data Compression Capable (DCC) bit of one indicates that the drive supports data compression and shall
process data sent to it for transferal to the medium using the selected compression algorithm when the DCE bit is
one. A DCC bit of ZERO indicates that the device does not support data compression. This shall be a
non-changeable field. The SDX-550V has the capability to decompress data and will set this bit to a one.
DDE: A Data Decompression Enable (DDE) bit of one indicates that data decompression is enabled. The SDX-550V
will always decompress the data. Setting this bit to ZERO has no effect.
RED: The Report Exception on Decompression (RED) field indicates the device's response to a boundary condition
caused by a change in the format of recorded data from:
uncompressed to compressed or compressed to uncompressed
This field only has an effect during reading not during writing. This field is not supported and should be always set to
00b.
RED Value
00b The SDX-550V will return a CHECK CONDITION status (MEDIUM ERROR) whenever data is
encountered on the media that the drive cannot decompress.
The SDX-550V will not return a CHECK CONDITION status at a boundary condition as long as the
data is uncompressed or ALDC1 compressed.
01b A RED field of 01b is undefined.
10b The drive shall return a CHECK CONDITION status whenever a boundary condition is encountered
on the medium. The boundary conditions are from:
uncompressed to compressed
or
compressed to uncompressed
CHECK CONDITION will be reported on the boundary condition even if the drive supports hardware
decompression.
For any of the boundary conditions which result in a CHECK CONDITION status, the additional
sense code shall be set to either DECOMPRESSION EXCEPTION, ALGORITHM ID OF NN. The
drive will set the decompression algorithm field to the algorithm identifier of the compression
algorithm used to process the encountered data. The device shall be positioned on the EOP side of
the encountered data, and the command-specific information field in the sense data shall contain a
count of the number of data blocks contained within the encountered data.
Note: When compressed data is encountered on the medium which the device cannot decompress,
the device should treat the data as a single variable-length record. In the sense data, the valid bit,
the ILI bit and the information field should be set accordingly.
11b A RED field of 11b is undefined.
Compression Algorithm: The compression algorithm field indicates the compression algorithm the drive will use to
process data sent to it by the initiator (if the DCE bit is one).
The SDX-550V supports the ALDC1 data compression algorithm which is identified by the value: 00 00 00 03h in the
compression algorithm field. A value of ZERO shall indicate that no compression algorithm is currently selected. Any
other values in this field will cause the drive to return a CHECK CONDITION status the sense key shall be set to
ILLEGAL REQUEST.
Decompression Algorithm: For MODE SELECT the decompression algorithm field indicates the decompression
algorithm selected by the initiator for use in subsequent decompression of data encountered on the medium.
The SDX-550V can decompress data recorded with the ALDC1 algorithm therefore this field can be set to 00 00 00
03h. However, the SDX-550V is capable of automatic recognition of the compression algorithm used to process the
data encountered on the medium. Therefore, the drive will override the value in the decompression field (if is set to
ZERO) for a subsequent read operation when ALDC1 compressed data is detected on the media.
A CHECK CONDITION will occur on the transition from uncompressed to compressed if RED=10b.
6-42
Description
SONY AIT-2 Turbo drive SDX-550V series Ver.1.0
MODE SELECT