RM23712 TPS
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threshold violation is detected again.
4.2.4 Fan Redundancy Detection
The BMC supports redundant fan monitoring and implements a fan redundancy sensor. A fan
redundancy sensor generates events when its 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 through OEM SDRrecords.
A fan failure or removal of hot-swap fans up to the number of redundant fans specified in the SDRin
a fan configuration is a non-critical failure and is reflected in the front panel status. A fan failure or
removal that exceeds the number of redundant fans is a non-fatal, insufficient-resources condition
and is reflected in the front panel status as a non-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.
4.2.5 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 BMCcontrols the average duty cycle of each PWM signal through direct manipulation of the
integrated PWM control registers.
The same device may drive multiple PWM signals.
4.2.6 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.
Chenbro customized SDRrecords 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 Chenbro customized SDRs can reference or control the same fan control domain;
and multiple Chenbro customized 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 by means of 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, for example, an SDR adhering to a
legacy format, the BMC assumes a hysteresis value of zero.
4.2.7 Thermal and Acoustic Management
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