Read Data Format; Thermal Data Update Rate; Temperature Comparator And Alert - Intel 6 SERIES CHIPSET - DATASHEET 01-2011 Datasheet

Functional Description
5.21.2.4

Read Data Format

For each of the data fields an ERROR Code is listed below. This code indicates that the
PCH failed in its access to the device. This would be for the case where the read
returned no data, or some illegal value. In general that would mean the device is
broken. The EC can treat the device that failed the read as broken or with some fail-
safe mechanism.
5.21.2.4.1 PCH and DIMM Temperature
The temperature readings for the PCH, DIMM are 8-bit unsigned values from 0–255.
The minimum granularity supported by the internal thermal sensor is 1 °C. Thus, there
are no fractional values for the PCH or DIMM temperatures.
Note the sensors used within the components do not support values below 0 degrees,
so this field is treated as 8 bits (0–255) absolute and not 2's complement (-128 to
127).
Devices that are not present or that are disabled will be set to 0h. Devices that have a
failed reading (that is, the read from the device did not return any legal value) will be
set to FFh. A failed reading means that the attempt to read that device returned a
failure. The failure could have been from a bus failure or that the device itself had an
internal failure. For instance, a system may only have one DIMM and it would report
only that one value, and the values for the other DIMMs would all be 00h.
5.21.2.5

Thermal Data Update Rate

The temperature values are updated every 200 ms in the PCH, so reading more often
than that simply returns the same data multiple times. Also, the data may be up to
200 ms old if the external controller reads the data right before the next update
window.
5.21.2.6

Temperature Comparator and Alert

The PCH has the ability to alert the external controller when temperatures are out of
range. This is done using the PCH TEMP_ALERT# signal. The alert is a simple
comparator. If any device's temperature is outside the limit range for that device, then
the signal is asserted (electrical low). Note that this alert does not use the
SML1ALERT#.
The PCH supports 4 ranges:
1. PCH range - upper and lower limit (8 bits each, in degrees C) for the PCH
temperature.
2. DIMM range - upper and lower limit (8 bits each, in degrees C), applies to all
DIMMs (up to 4 supported) that are enabled. Disabled (unpopulated) DIMMs do not
participate in the thermal compares.
3. Processor Package range - upper and lower limit (8 bits each, in degrees C)
The comparator checks if the device is within the specified range, including the limits.
For example, a device that is at 100 degrees when the upper limit is 100 will not trigger
the alert. Likewise, a device that is at 70 degrees when the lower limit is 70 will not
trigger the alert.
The compares are done only on devices that have been enabled by BIOS for checking.
Since BIOS knows how many DIMMs are in the system, it enables the checking only for
those devices that are physically present.
The compares are done in firmware, so all the compares are executed in one software
loop and at the end, if there is any out of bound temperature, the PCH's TEMP_ALERT#
signal is asserted.
Datasheet 233