Specifications

Processor Presence and Population Check QSSC-S4R Technical Product Specification
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the table lookup is saved for reference. When the final domain contribution is calculated, it is reduced, if necessary, to
this domain maximum value. This limits the maximum noise output of the system for a given ambient temperature to
ensure acoustic specifications are met.
Hysteresis is not applied to domain maximum sub-records.
24.13.4.2 Clamp
Clamp Tcontrol sub-records specify one 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. If the sensor reading exceeds the clamp value, then the fan speed contribution increases over time until either
the fan speed reaches saturation (maximum speed) or the temperature drops below the threshold. If the temperature is
below the threshold, the sensor’s contribution is reduced over time until it reaches zero. Fan speed changes occur in
the step size specified in the sub-record.
To keep a minor change in the temperature from causing a rapid and dramatic increase in the fan speed, these sub-
records allow a scan rate to be specified that lowers the frequency at which the sub-record’s contribution is
recalculated. Increasing the scan rate allows more time for increased cooling to take effect before increasing the fan
speed again.
If hysteresis is specified, it is only applied when the contribution direction might change from positive to negative or vice
versa. For example, if the BMC previously increased the fan speed contribution from a given clamp sub-record, it
factors in specified negative hysteresis when determining whether to change direction and start decreasing the fan
contribution. If no action is taken due to hysteresis, the BMC continues to remember the previous direction.
Figure 108. Clamp Control Hysterisis
Clamp controls associated with processor temperature sensors are special-case. They must have the “use Tcontrol bit
set” in the SDR sub-record and a 1-based processor number must be specified. The BMC uses the processor number
to look up the Tcontrol value received from BIOS for that processor. In the PECI implementation, the Tcontrol value is a
positive number representing a negative offset, so the BMC subtracts the Tcontrol value from the clamp threshold in
the SDR. This adjusted clamp threshold is used to determine fan speed contribution.
The sum of calculated contributions of all Clamp Tcontrol sub-records that are valid under the active profile for that
domain is added to the maximum of valid stepwise linear contributions.