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MODE SELSECT
RED Value
00b
The SDX-250V will return a CHECK CONDITION status (MEDIUM ERROR) whenever data is
encountered on the media that the drive cannot decompress.
The SDX-250V 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-250V 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-250V can decompress data recorded with the ALDC1 algorithm therefore this field can be set to 00 00 00
03h. However, the SDX-250V 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.
For the MODE SENSE command, the decompression algorithm field reflects either the algorithm selected by the
initiator or compression algorithm which was used to process the data most recently encountered on the medium,
during a read operation.
A value of ZERO shall indicate that the data encountered on the medium during the most recent read operation was
uncompressed.
SONY AIT-E Turbo drive SDX-250V series Ver.1.0
Description
6.Command Specification
6-31
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