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Product Manual - Hawk 2 Family SCSI-2 (Volume 1), Rev. B
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11.3.2
Mode Sense data
The Mode Sense command provides a means for the drive to report its operating parameters to the initiator. The
drive maintains four sets of Mode parameters, Default values, Saved values, Current values and Changeable
values.
Default values are hard coded in the drive firmware that is stored in flash E-PROM nonvolitile memory on the
drive PCB. Default values can be changed only by downloading 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.
Saved values are stored on the disk media using a Mode Select command. Only parameter values that are
allowed to be changed can be changed by this method. See "Changeable values" defined below. Parameters in
the Saved values list that are not changeable by the Mode Select command get their values from the Default
values storage.
Current values are volitile values currently being used by the drive to control its operation. A mode Select
command can be used to change these values (only those that are changeable). Originally, they are installed
from Saved or Default values after a power on reset, hard reset, or Bus Device Reset message.
Changeable values form a bit mask, stored in non-volatile memory, that dictates which of the Current values and
Saved values can be changed by a Mode Select command. A "one" allows a change to a corresponding bit; a
"zero" allows no change. For example, in Table 11.3.2-1a refer to Mode page 01, in the first row entitled "CHG".
These are hex numbers representing the changeable values for Mode page 01. Note in columns 1 and 2 (bytes
00 and 01), there is 00h, which indicates that in bytes 00 and 01 none of the bits are changeable. Note also that
bytes 04, 05, 06 and 07 are not changeable, because those fields are all zeros. In bytes 02, hex value FF equates
to the binary pattern 1111 1111. If there were a zero in any bit position in the field, it would mean that bit is not
changeable. However, bits 7 - 0 are changeable, because those bits are all ones. In this particular case, it
indicates 8 error recovery control bits are all changeable. FF in column 4 indicates all bits in byte 3 are change-
able.
The Changeable values list can only be changed by downloading new firmware into the flash E-PROM.
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.
When a drive is powered up, it takes Saved values from the media and stores them to the Current values storage
in volatile memory. It is not possible to change the Current values (or the saved values) with a Mode Select
command before the drive is up to speed and is "ready." An attempt to do so results in a "Check Condition" status
being returned. A subsequent Request Sense command returns Sense Key 02 with an error code of 04 02,
meaning "drive not ready, initializing command required.
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