Specifications

Processor Presence and Population Check QSSC-S4R Technical Product Specification
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the fan speed sensors and clears fan failure conditions. If the failure condition is still present, the boost state returns
once the sensor has reinitialized and the threshold violation is detected again.
24.13.2 Fan Redundancy Detection
The BMC supports redundant fan monitoring and implements a fan redundancy sensor. A fan redundancy sensor
generates events when it’s associated set of fans transitions between redundant and non-redundant states, as
determined by the number and health of the fans. The definition of fan redundancy is configuration dependent. The
BMC allows redundancy to be configured on a per fan-redundancy sensor basis via OEM SDR records.
A fan failure, or removal of hot-swap fans up to the number of redundant fans specified in the SDR, in a fan
configuration is a degraded failure and is reflected in the front panel status as such. A fan failure or removal that
exceeds the number of redundant fans is a fatal insufficient resources 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 changes that occur when the
system is DC-off, or when AC is removed will not be logged until the system is turned-on.
24.13.3 Fan Domains
System fan speeds are controlled through pulse width modulation (PWM) signals, which are driven separately for each
domain by integrated PWM hardware. Fan speed is changed by adjusting 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 of the integrated PWM
control registers.
See the Chassis Management section for fan mapping information.
24.13.4 Nominal Fan Speed
A fan domain’s nominal fan speed can be configured as 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
and the algorithmic relationship between the temperature and fan speed. Multiple OEM SDRs can reference or control
the same fan control domain, and multiple OEM SDRs can reference the same temperature sensors.
The PWM duty-cycle value for a domain is computed as a percentage 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 another is
ramped over time to minimize audible transitions. The ramp rate is configurable via the OEM SDR.
Multiple stepwise linear and clamp controls can be defined for each fan domain and used simultaneously. For each
domain, the BMC uses the maximum of the domain’s stepwise linear control contributions and the sum of the domain’s
clamp control contributions to compute the domain’s PWM value, except that a stepwise linear instance can be
configured to provide the domain maximum.
Hysteresis can be specified to minimize fan speed oscillation and to smooth fan speed transitions. If a Tcontrol SDR
record does not contain a hysteresis definition, e.g. an SDR adhering to a legacy format, the BMC will assume a
hysteresis value of zero.
24.13.4.1 Stepwise Linear
24.13.4.1.1 Fan Speed Contribution
Each stepwise linear Tcontrol sub-record defines a lookup table that maps temperature sensor readings to fan speeds.
The table entries must be in increasing order of temperature. The BMC goes through the table, starting from the end,
until it finds a temperature entry that is less than or equal to the current reading of the associated temperature sensor.
The corresponding fan speed is used as the domain fan contribution of that sub-record. If the current reading is less
than 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 Control SDR.
The basis for the final fan speed for each domain is the maximum of calculated contributions of stepwise linear Tcontrol
sub-records that are valid under the active profile for that domain. All valid clamp contributions are added to this base
value.
If no hysteresis is specified in the stepwise linear sub-record, then each reading is used to recalculate the fan speed
contribution. This can result in oscillating fan behavior if the sensor reading alternates between two different values.
The frequent change in fan speed can be irritating and might be interpreted as improper system behavior.