Using the MPI to Check the Temperature

To assist users in monitoring the eXMP's temperature, a Temperature Monitoring Feature has been added into the MPI that retrieves the junction temperature of the die (T_junction) on the eXMP. MEI recommends that all users set periodic checks of the T_junction and also set appropriate temperature limits in their application code.

The following methods can be found in platform.h in these software releases:
        VxWorks: 20030605 and later
        Linux: 03.03.00 and later (also available in 20030620.1.7)
        XP Embedded: 03.03.00 and later

	meiPlatformExmpTempInit(MEIPlatform platform)
		Initialize the onboard monitor chip (LM87) for temperature reads. Must be run at every power cycle (or reset).

meiPlatformExmpTempGet(MEIPlatform platform,
long* temp)

Returns the temperature of the on-board Celeron processor (T_junction) in degrees C.

NOTE: This is not the temperature of the eXMP case or the environmental temperature. It is the internal temperature of the die.

Recommendations

Environmental Temperature: 0 to 50 degrees C
Die Temperature (T_junction) : < 90 degrees C

It is recommended that all users include the temperature checking methods in order to safely monitor the temperature of the processor in order to prevent an unexpected shutdown of the computer. In the event of a fan failure, the T_junction can quickly rise to its failure limit in certain conditions.

Generally speaking, the T_junction has a greater chance of reaching its failure limit if:

the environmental temperature of the eXMP is near 50 degrees C.
the eXMP is in an area where there is little air circulation.

Therefore, depending on the type of environment of the eXMP, it is best to set appropriate temperature checks and limits.

Tests

Several tests were performed at MEI facilities that showed the following behavior. These tests should NOT be used as guidelines for your machine. They simply provide rough estimates that can help you set appropriate temperature limits for your machine.

CASE 1
Environmental temperature = 23 degrees C.
Chamber airflow = 0CFM

An eXMP shutdown occurred approximately 75 minutes after a simulated fan failure.

CASE 2
Environmental temperature = 50 degrees C.
Chamber airflow = 0CFM

A eXMP shutdown occurred approximately 33 minutes after a simulated fan failure.

The Bottom Line

It is important for all users to use the eXMP temperature checking methods in their application code to periodically monitor the T_junction in order to ensure that the necessary precautions can be made (in the event of a fan failure) prior to any potentially damaging over temperature failure.