User's Guide

Page 52 DDS-4 SCSI Interface Manual, Rev. B
The drive presets the values as follows:
• The default accumulated values are set to all 0s.
• The default threshold values are set to all 1s.
The default values cannot be changed. If the host issues a LOG SELECT command
with the PC bit specifying default values when the parameter list length is nonzero, a
Check Condition is returned. The sense data is set to Illegal Request, Invalid Field in
the CDB.
The Parameter Control bytes of each parameter are preserved when the LOG
SELECT command is issued with the PC bits specifying either of the default values.
SETTING ACCUMULATED VALUES DIRECTLY
The host can set the accumulated values of pages 2 and 3 to any value by
specifying the accumulated values in the PC bits and transferring the log parameters
containing the new values and the Parameter Control bytes.
This ability to manually set the accumulated values allows the original counts
previously read with the LOG SENSE command to be restored. Thus, the drive can
continue to accumulate counts after a Bus Reset, Bus Device Reset, or a manual
power cycle.
SETTING THE THRESHOLD VALUES DIRECTLY
The host can set the threshold values of pages 2 and 3 to any value by specifying
the threshold values in the PC bits and transferring the log parameters containing
the new values and the Parameter Control bytes.
The threshold value is used in conjunction with the Log Parameter Control byte of
the log data and the RLEC bit of the Mode Select/Sense Control Mode page to
determine if, and when, a log exception Check Condition should be generated when
an accumulated count is incremented.
MAXIMUM COUNTS
Threshold values are not the same as the maximum count. The maximum size of
each counter is according to the size of the counter in bytes. When the maximum
count is reached, the DU bit in the Parameter Control byte for the counter is set to 1
for the Log Sense data indicating that the parameter is no longer to be updated
because the maximum count has been reached.
When a counter reaches the maximum, the counter is no longer incremented. If a
maximum value for the parameter size is reached, the count does NOT roll over and
continue counting. When any counter of a page reaches maximum, all counters of
that page are no longer incremented. A LOG SELECT command can be issued with
the PC bits specifying default accumulated values to reset the accumulated values
and to allow counters to continue as normal. The DU bit of the affected parameter is
also reset to zero.
LOG SELECT Parameter Data
The host should issue a LOG SENSE command to initialize host software that
allows