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ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCT DESCRIPTION MANUAL
C.3.3 Compression Algorithm---Byte 07
The Compression Algorithm byte (07) of the MODE SENSE page specifies the algorithm used to compress
da ta when the DCE bit is 1.
o
A value of 20h in this byte specifies the DCLZ algorithm, which is the default. If the host selects a
value of 01h, for the default algorithm, a value of 20h is returned by the MODE SENSE data.
o
A value of OOh specifies that data compression is disabled.
C.3.4 Decompression Algorithm--Byte 11
The Decompression Algorithm byte (11) of the MODE SENSE page is specified by the Python drive to
indicate the compression algorithm used on the data that was last read to the host This byte is valid whether
or not the drive decompresses the data. The byte defaults to a value of 20h to indicate DeLZ decompression.
Table C-S shows the algorithm values and meaning.
Algorithm
00
20
01-1F
21-FF
Table
C-S.
Algorithms---MODE SENSE Page
Description
Data last sent to the host was uncompressed.
Data last sent to the host was compressed using the DClZ algorithm.
Data last sent to the host was compressed using an algorithm other
than the DClZ algorithm. The contents of the DDS-DC entity header
algorithm byte is returned.
C.4 Request Sense Data
During reading, several exception conditions can occur that cause the Python DDS-DC drive to send data to
the host in the compressed DDS-DC entity format. The following cases cause compressed data to be sent to
the host
o
Decompression is disabled and the Python drive encounters compressed data.
o
The Python drive encounters data that was compressed with an algorithm other than the DCLZ
algorithm.
In the above cases, the Python DDS-DC drive sends the compressed entity to the host and tenninates the
READ command with a Check Condition status. An additional Sense. Code of 70h is used to indicate a
Decompression Exception Condition. The Additional Sense Code Qualifier field is used to indicate the
algorithm in the entity header that was used to compress the data.
The entity is returned as a single block. The Valid and Incorrect Length Indicator (ILl) bits are set
appropria tel y.
Table C-6 lists the Sense Data values.
C-6
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