Specifications

Processor Presence and Population Check QSSC-S4R Technical Product Specification
280
Power supply fan sensors are implemented as manual re-arm sensors because a failure condition can result in
boosting of the fans. This in turn may cause a failing fan’s speed to rise above the “fault” threshold and can result in fan
oscillations. As a result, these sensors do not auto-rearm when the fault condition goes away but rather are rearmed
only when the system is reset or power-cycled.
After the sensor is rearmed, if the fan is no longer showing a failed state, the failure condition in the IPMI sensor shall
be cleared and a deassertion event shall be logged.
IPMI Sensor Characteristics
x Event reading type code: 03h (Generic – digital discrete)
x Sensor type code: 04h (Fan)
x Rearm type: Manual
Table 184. Supported Sensor Offsets
Offset Description Event Logging
01h State asserted Assertion and deassertion
24.25.3 Power Supply Fan Speed Control
A component of QSSC-S4R thermal management is BMC control of power supply fan speed. All control of power
supply fans by the BMC is done via PMBus commands. Note that PMBus fan control commands use RPM values
rather than PWM values as is used for fans that are connected directly to the IBMC fan PWM outputs (refer to the
applicable power supply specifications for details of PWM vs RPM fan control capabilities). The fan control OEM SDRs
used for power supply control will therefore specify the control data as RPM values. In order for the fan speed control
logic to work correctly, the SDRs must be reloaded any time the power supply configuration is changed in order to load
the proper SDRs for the given power supplies.
Power supplies have internal fans which provide cooling to the power supplies and to the hard disks. The power supply
fan speed control is influenced by the power supply internal logic along with system level control. The power supply
fans operate from distributed 12V power. If a power supply is installed, the power supply fans will always have 12V
power applied and allow full PMBUS control, even if the power supply is failed.
The following factors will influence the power supply fan speed.
1. Internal control. Internal control is based on an internal temperature sensor along with power supply load. These
details are documented in the power supply specification.
2. Front Panel Thermal Sensor Clipping curves. The front panel sensor must be mapped via the piecewise upper and
lower clipping curves to the power supply fans.
3. Lookup Table. In order to sufficiently cool the hard disks, the power supply fans speed must also react to the main
system fans speeds. Since the main system fans are in four fan zones, the maximum aggregate system fan speed
will be used in the lookup table. The following table shows an example of the lookup table. The specific values in
the lookup table will be based on system testing. The table should be flexible and allow values to be changed
through an SDR mechanism. There must be a unique lookup table for each power supply configuration. This
results in four lookup tables, one for each power supply configuration. The lookup table will specify a power supply
fan RPM.
Table 185. Example PS Fan Lookup Table
Maximum
System
Fan
Speed
PWM
Minimum Power Supply Fan RPM
One PS
Module
Two PS
Modules
Three PS
Modules
Four PS
Modules
20
Always at
100%
55% 45% 40%
30 55% 45% 40%
40 55% 45% 40%
50 Linear Linear Linear
60