Sun Microsystems Enterprise 250 Owner's Manual page 106

Monitoring and control capabilities reside at the operating system level as well as in
the system's flash PROM firmware. This ensures that monitoring capabilities are
operational even if the system has halted or is unable to boot.
2
The environmental monitoring subsystem uses an industry standard I C bus
2
implemented on the main logic board. The I C bus is a simple two-wire serial bus,
used throughout the system to allow the monitoring and control of temperature
sensors, fans, power supplies, and status LEDs.
Temperature sensors are located throughout the system to monitor the ambient
temperature of the system and the temperature of each CPU module. The monitoring
subsystem frequently polls each sensor and uses the sampled temperatures to:
4 Regulate fan speeds for maintaining an optimum balance between proper cooling
and noise levels.
4 Report and respond to any over-temperature conditions.
To indicate an over-temperature condition, the monitoring subsystem generates a
warning message, and depending on the nature of the condition, may even shut
down the system. If a CPU module reaches 60 degrees C or the ambient temperature
reaches 53 degrees C, the system generates a warning message and illuminates the
temperature fault LED on the status and control panel. If a CPU module reaches 65
degrees C or the ambient temperature reaches 58 degrees C, the system is
automatically shut down.
This thermal shutdown capability is also built into the main logic board circuitry as a
fail-safe measure. This feature provides backup thermal protection in the unlikely
event that the environmental monitoring subsystem becomes disabled at both the
software and firmware levels.
All error and warning messages are displayed on the system console (if one is
attached) and are logged in the /var/adm/messages file. Front panel fault LEDs
remain lit after an automatic system shutdown to aid in problem diagnosis.
The monitoring subsystem is also designed to detect fan failures. The system
includes three fans, part of a single assembly called the fan tray assembly. Any fan
failure causes the monitoring subsystem to generate an error message and light the
general fault LED on the status and control panel.
The power subsystem is monitored in a similar fashion. The monitoring subsystem
periodically polls the power supply status registers for a power supply OK status,
indicating the status of each supply's +2.5V, +3.3V, +5V, +12V, and -12V DC outputs.
If a power supply problem is detected, an error message is displayed on the console
(if one is attached) and logged in the /var/adm/messages file. The power supply
LED on the status and control panel is also lit. The LEDs located on the power
supply itself will indicate the type of fault, and if two power supplies are installed,
will indicate which supply is the source of the fault.
For more information about error messages generated by the environmental
monitoring subsystem, see "Environmental Failures" on page 273. For additional
Sun Enterprise 250 Server Owner's Guide ♦ Revision A, June 1998
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