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11.3.2
Mode Sense data
The Mode Sense command provides a way for the drive to report its operating parameters to the initiator. The drive maintains four sets of
mode parameters:
1.
Default values
Default values are hard-coded in the drive firmware stored in flash E-PROM (nonvolatile memory) on the drive’s PCB. These default
values can be changed only by downloading a complete set of new firmware into the flash E-PROM. An initiator can request and
receive from the drive a list of default values and use those in a Mode Select command to set up new current and saved values, where
the values are changeable.
2.
Saved values
Saved values are stored on the drive’s media using a Mode Select command. Only parameter values that are allowed to be changed
can be changed by this method. Parameters in the saved values list that are not changeable by the Mode Select command get their
values from default values storage.
When power is applied to the drive, it takes saved values from the media and stores them as current values in volatile memory. It is not
possible to change the current values (or the saved values) with a Mode Select command before the drive achieves operating speed
and is “ready.” An attempt to do so results in a “Check Condition” status.
On drives requiring unique saved values, the required unique saved values are stored into the saved values storage location on the
media prior to shipping the drive. Some drives may have unique firmware with unique default values also.
On standard OEM drives, the saved values are taken from the default values list and stored into the saved values storage location on
the media prior to shipping.
3.
Current values
Current values are volatile values being used by the drive to control its operation. A Mode Select command can be used to change the
values identified as changeable values. Originally, current values are installed from saved or default values after a power on reset,
hard reset, or Bus Device Reset message.
4.
Changeable values
Changeable values form a bit mask, stored in nonvolatile memory, that dictates which of the current values and saved values can be
changed by a Mode Select command. A one (1) indicates the value can be changed. A zero (0) indicates the value is not changeable.
For example, in Table 10 refer to Mode page 01, in the row entitled “CHG.” These are hex numbers representing the changeable val-
ues for Mode page 01. Note in columns 5 and 6 (bytes 04 and 05), there is 00h which indicates that in bytes 04 and 05 none of the bits
are changeable. Note also that bytes 06, 07, 09, 10, and 11 are not changeable, because those fields are all zeros. In byte 02, hex
value FF equates to the binary pattern 11111111. If there is a zero in any bit position in the field, it means that bit is not changeable.
Since all of the bits in byte 02 are ones, all of these bits are changeable.
The changeable values list can only be changed by downloading new firmware into the flash E-PROM.
Note.
Because there are often several different versions of drive control firmware in the total population of drives in the field, the
Mode Sense values given in the following tables may not exactly match those of some drives.
The following tables list the values of the data bytes returned by the drive in response to the Mode Sense command pages for SCSI
implementation (see the SAS Interface Manual
).
DEF = Default value. Standard OEM drives are shipped configured this way.
CHG = Changeable bits; indicates if default value is changeable.
