IntelÃ‚Â® Server System Server System "Emerald Ridge ... - CTL

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錯誤 ! 尚未定義樣式。 EPSFunctional SpecificationA fan failure, or removal of hot-swap fans up to the number of redundant fans specified in theSDR, in a fan configuration is a degraded failure and is reflected in the front panel status assuch. A fan failure or removal that exceeds the number of redundant fans is a fatal insufficientresources condition and is reflected in the front panel status as a fatal error.Redundancy is checked only when the system is in the DC-on state. Fan redundancy changesthat occur when the system is DC-off, or when AC is removed will not be logged until the systemis turned-on.See the Chassis Management section for chassis specific fan redundancy configuration.3.16.3 Fan Domains<strong>System</strong> fan speeds are controlled through pulse width modulation (PWM) signals, which aredriven separately for each domain by integrated PWM hardware. Fan speed is changed byadjusting the duty-cycle, which is the percentage of time the signal is driven high in each pulse.The BMC controls the average duty-cycle of each PWM signal through direct manipulation ofthe integrated PWM control registers.See the Chassis Management section for fan mapping information.3.16.4 Nominal Fan SpeedA fan domain’s nominal fan speed can be configured as static (fixed value) or controlled by thestate of one or more associated temperature sensors.OEM SDR records are used to configure which temperature sensors are associated with whichfan control domains and the algorithmic relationship between the temperature and fan speed.Multiple OEM SDRs can reference or control the same fan control domain, and multiple OEMSDRs can reference the same temperature sensors.The PWM duty-cycle value for a domain is computed as a percentage using one or moreinstances of a stepwise linear algorithm and a clamp algorithm. The transition from onecomputed nominal fan speed (PWM value) to another is ramped over time to minimize audibletransitions. The ramp rate is configurable via the OEM SDR.Multiple stepwise linear and clamp controls can be defined for each fan domain and usedsimultaneously. For each domain, the BMC uses the maximum of the domain’s stepwise linearcontrol contributions and the sum of the domain’s clamp control contributions to compute thedomain’s PWM value, except that a stepwise linear instance can be configured to provide thedomain maximum.Hysteresis can be specified to minimize fan speed oscillation and to smooth fan speedtransitions. If a Tcontrol SDR record does not contain a hysteresis definition, e.g. an SDRadhering to a legacy format, the BMC will assume a hysteresis value of zero.3.16.4.1 Stepwise Linear3.16.4.1.1 Fan Speed ContributionEach stepwise linear Tcontrol sub-record defines a lookup table that maps temperature sensorreadings to fan speeds. The table entries must be in increasing order of temperature. The BMCRevision 1.1Intel ® Confidential 29
錯誤 ! 尚未定義樣式。錯誤 ! 尚未定義樣式。 EPSgoes through the table, starting from the end, until it finds a temperature entry that is less thanor equal to the current reading of the associated temperature sensor. The corresponding fanspeed is used as the domain fan contribution of that sub-record. If the current reading is lessthan all temperature entries in the table, then the sub-record’s contribution remains unchanged.Fan speed shall not drop below the nominal value given in the Temperature Fan Speed ControlSDR.The basis for the final fan speed for each domain is the maximum of calculated contributions ofstepwise linear Tcontrol sub-records that are valid under the active profile for that domain. Allvalid clamp contributions are added to this base value.If no hysteresis is specified in the stepwise linear sub-record, then each reading is used torecalculate the fan speed contribution. This can result in oscillating fan behavior if the sensorreading alternates between two different values. The frequent change in fan speed can beirritating and might be interpreted as improper system behavior.Such oscillation can be prevented by specifying positive or negative hysteresis, or both. Eachtime the fan speed contribution is calculated, the BMC uses the hysteresis values to create awindow around the temperature value that was used for the calculation. The fan speed and thehysteresis window remain unchanged until a new sensor reading falls outside of the window.The process repeats with that new reading: it is used to recalculate the fan speed contributionand define a new hysteresis window. This cycle is independent of the lookup table values andapplies regardless of whether the new temperature reading affects the fan speed contribution.The BMC creates this window by applying the hysteresis values as follows:1. A new reading is retrieved from the BMC’s sensor subsystem.2. The last-applied reading, the reading that was used to calculate the sub-record’s current fanspeed contribution, is subtracted from the new reading.3. Hysteresis is applied to the difference:• If the difference is positive (the new reading is higher), the positive hysteresis issubtracted from the difference.• Otherwise, the change is non-positive (negative or zero), and the negative hysteresis isadded to the difference.4. The modified difference is evaluated:• If factoring in the hysteresis changed the calculated difference from positive to negativeor from non-positive to positive, the new reading is ignored and the previously calculatedfan speed contribution is used.• Otherwise, the reading obtained in step 1 is used to recalculate the fan speedcontribution, and it is used as the last applied reading until the hysteresis window isexceeded again.For example, if a stepwise linear sub-record specifies a positive hysteresis value of 3º C and anegative hysteresis of 2º C for an ambient temperature sensor. A sensor reading of 25º C isused to calculate the initial fan speed contribution for the sub-record. With the given hysteresis30Intel ConfidentialRevision 1.1
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