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Intel® 5000 Series Chipsets Server Board Family Datasheet
4.14.1
Nominal Fan Speed
It is possible to configure a fan domain's Nominal fan speed to be either static (fixed value) or
controlled by the state of one or more associated temperature sensors.
OEM SDR records are used to configure which temperature sensors are associated with which
fan control domains as well as the relationship (algorithm) between the temperature and fan
speed control (PWM) value. Multiple OEM SDRs may reference / control the same fan control
domain and multiple OEM SDRs may reference the same temperature sensors.
The PWM value for the given domain is computed using one or more instances of a stepwise
linear algorithm and a clamp algorithm. The transition from one computed Nominal fan speed
(PWM value) to a new one is ramped over time to avoid audible transitions. The ramp rate is
configurable via the OEM SDR.
Multiple Additive and Clamp Controls can be defined for each fan domain and used
simultaneously. For each domain, the BMC uses the maximum of all of the domain's Stepwise
Linear Control contributions and the sum of all of the domain's Clamp Control contributions to
computes the domain's total PWM value, with the exception that a stepwise linear instance can
be configured to provide the domain maximum at any time.
Hysteresis may be specified to minimize fan speed oscillation and also to smooth out fan speed
transitions. Its application is described along with the fan contribution methods below. If a
legacy T
SDR format does not allow specifying hysteresis, the BMC will assume a
CONTROL
hysteresis value of zero.
4.14.2
Stepwise Linear
4.14.2.1
Fan Speed Contribution
Each Stepwise Linear T
sensor readings to fan speeds. The table entries must be in increasing order of temperature.
The BMC walks the table, starting from the end, until it finds a temperature entry that is less
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
domain. All currently valid clamp contributions are added to this base value.
Revision 1.1
sub-record defines a lookup table that maps temperature
CONTROL
sub-records that are valid under the active profile for that
CONTROL
Intel order number D38960-004
System Management
119
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