Server Board Family Datasheet

Intel® S5000 Server Board Family Datasheet System Management
Revision 1.3
Intel order number D38960-006
131
than or equal to the current reading of the temperature sensor. The corresponding fan speed is
used as the domain fan contribution of that sub-record.
Hysteresis is applied to the difference calculated from the previously used reading to the current
reading. If the difference is positive, the temperature is increasing and the specified positive
hysteresis is subtracted. Otherwise, the change is negative or zero (non-positive), and the
specified negative hysteresis is added.
If factoring in the hysteresis changes the calculated difference from positive to negative, or from
non-positive to positive, the previously calculated contribution is used instead of recalculating
the contribution. This is different from the IPMI sensor threshold interpretation of hysteresis,
which is applied to threshold, but it has the desired effect of preventing oscillating fan speed
behavior.
The basis for the final fan speed for each domain is the maximum of all calculated contributions
of all Stepwise Linear T
CONTROL sub-records that are valid under the active profile for that
domain. All currently valid clamp contributions are added to this base value.
4.14.2.2 Domain Maximum
Stepwise Linear T
CONTROL sub-records might have a flag set that indicates that the instance
provides the fan domain maximum PWM value. These sub-records do not contribute to the fan
speed as described above. Instead, the fan speed obtained through the table lookup procedure
is saved for later reference. When the final domain contribution is calculated, it will be reduced,
if necessary, to this domain maximum value. Hysteresis is not applied to domain maximum sub-
records.
4.14.3 Clamp
Clamp TCONTROL sub-records specify a single temperature value and direct the BMC to
increase the fan speed for the associated fan domain as necessary to maintain the value of the
corresponding temperature sensor below the clamp value. When the sensor reading exceeds
the clamp value, the fan speed contribution will increase over time until either the fan speed
reaches maximum speed or the temperature reduces to below the threshold. If the temperature
is below the threshold, the sensor’s contribution will be reduced over time until it goes to zero.
Fan speed changes occur in the step size specified in the sub-record.
These sub-records allow a scan rate to be specified that will lower the frequency at which the
sub-record’s contribution is recalculated. This can be used to allow time for the fan domain to
react and increase the system cooling before increasing the fan speed again.
Hysteresis, if specified, is only applied when the contribution direction might change from
positive to negative or vice versa. e.g., if the BMC previously increased the fan speed
contribution from a given clamp sub-record, it will factor in any specified negative hysteresis
when determining whether the “change direction” and start decreasing the fan contribution. If no
action is taken due to hysteresis, the BMC continues to remember the previous direction.
The sum for all calculated contributions of all Clamp T
CONTROL sub-records that are valid under
the currently active profile for that domain will be added to the maximum of all currently valid
stepwise linear contributions.