User's Guide

Commands: Log Select (4Ch) Page 55
issued to specify the control bytes for the threshold parameter, the accumulated
Parameter Control byte is affected. The LOG SENSE data reflects the current
setting of the control byte for the parameter.
The Parameter Control byte bits used by the drive are described in the following
table.
Bit Name Bytes Bits Description
Disable
Update (DU)
2 7 When set (1), this bit indicates that the host does not want this
counter to be updated.
Enable
Threshold
Comparison
(ETC)
2 4 When set (1), this bit enables the generation of a Check
Condition when an accumulated counter is incremented and
the new value meets the threshold criteria (and MODE
SELECT/SENSE Control Mode Page RLEC bit is set). See the
following heading, Use of the TMC Field and the ETC Bit.
Threshold Met
Criteria Field
(TMC)
2 3-2 This field indicates when a Check condition should be
generated when the ETC bit is set and a counter is updated
(and MODE SELECT/SENSE Control Mode Page RLEC bit is
set). See the following heading, Use of the TMC Field and the
ETC Bit.
The Parameter Length byte is the byte count of the parameter value that is being
sent. This length must be equal to the length returned by the LOG SENSE
command.
The Parameter Value bytes indicate the value of the selected parameter type
indicated in the CDB Parameter Code field. The initiator must select either the
accumulated or threshold values by the PC bits of the LOG SELECT CDB to send
Parameter Value bytes.
USE OF THE TMC FIELD AND THE ETC BIT
The Threshold Met Criteria (TMC) field specifies how and when a log exception is to
be reported to the host. The Enable Threshold Comparison (ETC) bit enables or
disables the generation of a Check Condition for log exceptions of individual log
parameters. The Report Log Exception Condition (RLEC) bit of the MODE
SELECT/SENSE Control Mode Page, when set, allows the generation of a Check
Condition for log exceptions for each log parameter whose ETC bit is set.
An RLEC bit of zero globally disables all log exception Check Conditions regardless
of the ETC bit value of each log parameter.
When the ETC bit is set (1) (and the RLEC bit is set in the MODE SELECT/SENSE
Control Mode Page), a Check Condition is generated each time the accumulated
value is incremented and the threshold condition is met as described in the following
paragraphs.
When a counter is incremented by the drive, a check is made to determine if the
threshold comparison is enabled (according to the ETC bit) for the counter being
incremented. If comparisons are enabled, the new accumulated value is compared
with the threshold value according to the Threshold Met Criteria for the counter.
When the criteria are met (and the RLEC bit is set in the MODE SELECT/SENSE
Control Mode Page), a log exception Check Condition is returned for the next
command. The sense key is set to Unit Attention (06); the additional sense code is