Section 5 SCSI Programming Guidelines
5.11.10.6 Quantum Unigue Control Parameters. Page Code 37H
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B·t
Byte
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7
6
5 4
3
2 1 o
0 RESERVED = 0
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PAGE CODE = 37H
1
PAGE LENGTH =
OEH
2 RESERVED
=0
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PSM
I
SSM
I
WIE
I
PO
I
PE
J
CE
3
NUMBER
OF
CACHE SEGMENTS
4
MINIMUM PREFETCH
5 MAXIMUM PREFETCH
6-15
RESERVED=O
PSM
-
PRESERVE
SYNCHRONOUS
MODE
(Byte
2,
Bit 5) - Set to one indicates the
ProDrive will not clear the table
of
synchronous mode parameters for all initiators when the drive is
reset. A
PSM bit set to zero will cause all these parameters to be cleared when the drive
is
reset. The
default is zero.
SSM
-
SEND
SYNCHRONOUS
MESSAGE
(Byte 2, Bit 4) - Set to one indicates that
the
ProDrive will initiate sending the Extended Message (01) Synchronous Data Transfer Request to
the initiator. A
SSM bit set to zero indicates that the initiator must initiate sending the Synchronous
Data Transfer Request message. The default
is
zero.
NOTE: The following parameters control the operation
of
Quantum's unique DisCache feature. See
Appendix A for a description
of
DisCache, and more information on these options.
WIE
-
WRITE
INDEX:
ENABLE
(Byte 2, Bit 3) - All data from WRITES create a cache
segment stored
in
the cache and indexed by the cache table. A WIE bit set to zero indicates that the
ProDrive will overwrite this segment in the cache on the next READ
or
WRITE. A WIE bit set to
one indicates that the
ProDrive will treat this segment as
if
it had been generated by a READ.
Setting WIE to zero preserves more data in the cache from READs, increasing the likelihood that the
data for subsequent READ requests will be
in
the cache; the magnitude
of
this increase depends on the
size and frequency
of
WRITE requests. The default is zero.
PO
-
PREFETCH
ONLY
(Byte 2,
Bit
2) - Set to one indicates that the ProDrive will only
retain prefetch data in the cache; the originally requested read data will
be overwritten with prefetch
data. A PO bit set to zero indicates that both original read data and prefetched data will be retained
in
the segment. The default is zero.
PE
-
PREFETCH
ENABLE
(Byte 2,
Bit
1)
- Set to one indicates that the ProDrive will
perform prefetching. A PE bit set to a value
of
zero indicates that no prefetching will occur. The CE
bit must be set to one to enable use
of
the PE bit. The default
is
one.
CE
-
CACHE
ENABLE
(Byte 2
Bit
0) - Set to one indicates that the ProDrive will activate
caching on all
READS. A CE bit set to zero indicates that the ProDrive will disable caching and
use the 64K RAM as a transfer buffer only. The default
is
one.
NUMBER
OF
CACHE
SEGMENTS
(Byte 3) - Indicates to the ProDrive the number
of
segments to index in the cache, i.e., the number
of
entries
in
the cache table. Valid entries are
1,2,4,
8,
16.
Any other entry will result in a CHECK CONDITION status with a sense key
of
ILLEGAL
REQUEST. The default
is
four.
5-50
SCSI
Programming
Guidelines
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