Specifications

Processor Presence and Population Check QSSC-S4R Technical Product Specification
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24.13.5.2 ASHRAE Compliance
System requirements for ASHRAE compliance is defined in the Common Fan Speed Control & Thermal Management
Platform Architecture Specification. Altitude-related changes in fan speed control are handled through profiles for
different altitude ranges.
24.14 DIMM Thermal Margin Sensor
QSSC-S4R platform supports system memory DIMMs with temperature sensing capabilities. DIMMs without
temperature sensor are not supported. This section describes how the temperature readings from the DIMMs are
modeled as IPMI sensors.
SDRs for these aggregate sensors should be set to “sensor scanning disabled” state and that enabling/disabling of the
sensors occurs by the BMC FW when BIOS updates DIMM map using “Set Fan Control Configuration” command.
24.14.1.1 Discovery of Physical DIMM Temperature Sensors
The BIOS provides Physical DIMM presence information to the BMC using an IPMI command “Set Fan Control
Configuration” during POST at each system boot as part of BIOS configuration of the BMC fan settings.
During Memory Hot Plug and Memory Online/Offline, BIOS must update BMC regarding new DIMM presence map.
The temperature readings from the physical temperature sensors on each DIMM are aggregated into IPMI temperature
margin sensors for each for memory risers 1&2, 3&4, 5&6, and 7&8 corresponding to CPU group 0,1,2,3.
Each DIMM can potentially have a different nominal thermal operating range depending on the manufacturer, memory
refresh rate, and other factors. Taking these factors into account, BIOS programs one or more memory throttling
temperature thresholds into the memory throttling subsystem during POST. These thresholds define the DIMM
temperature value for which different levels of memory throttling take effect.
The BMC uses one of these thresholds as the reference point to calculate the current temperature margin for an
individual DIMM sensor. The DIMM with the most positive margin is considered the dominant margin of the group. This
value becomes the current sensor reading for the aggregate (IPMI) DIMM temperature sensor.
Once the BMC has received notification that the DIMM temp sensor and memory throttling configuration has
completed, the BMC will enable any aggregate DIMM margin sensors defined for the platform only if the throttling
mode is CLTT ( OLTT DIMMs are not supported)and there are valid DIMM temp sensors present that are associated
with the specific aggregate DIMM margin sensor.
If DIMMs with temperature sensors are present in the system and BMC monitoring of the DIMM temperatures is
enabled, then the BMC will periodically poll for these temperature readings in 3 second of scan rate. These aggregate
sensors are primarily used as input to the system fan management control algorithms but may also be used for
reporting temperature margin information and SEL logging.
This sensor is unavailable during a memory hot-plug or memory on-line/off-line operation that is performed on a
memory board associated with this sensor.
These sensors are implemented as auto-rearm threshold margin sensors.
24.14.1.2 DIMM Temperature Input to Fan Control Algorithm
The BMC can use aggregate margin sensor as the input for a clamp algorithm that increases fan speed if the margin
exceeds a given clamp value. Each supported aggregate sensor may be used as a control input for one or more fan
control domains. This configuration is specified using TControl OEM SDRs.
To support user choices regarding acoustic targets versus memory performance options, the fan control algorithm can
utilize a different margin clamp value for each option. This is implemented by using different Tcontrol SDRs for the Fan
Profiles associated with each option.
A negative aggregate margin sensor value means that all DIMMs are below their T1 values and no temperature-based
memory throttling is in effect.
If that sensor is linked to a Tcontrol Clamp sub-record with a negative clamp point, the BMC increases fan speed
before temperature-based throttling takes effect. This is associated with a performance-optimized profile.
If an aggregate margin sensor is linked to a Tcontrol Clamp sub-record with a positive clamp point, temperature-based
throttling takes effect before the BMC increases the fan speed. This is associated with an aggressively acoustics-
optimized profile. Acoustics-optimized profiles may also use negative clamp points and rely on more aggressive
memory throttling (configured by BIOS) to reduce the overall cooling requirements.