Thermal Sensors
This page aims to summarize known information about the locations and properties of thermal sensors on ThinkPad laptops.
Contents
Accessing the sensors
The primary means of accessing the thermal sensors is through the ibm-acpi module, which provides up to 11 thermal sensors (some of which may be inactive) when loaded with the experimental=1 option. Up to eight thermal sensors are exposed at /proc/acpi/ibm/thermal:
# cat /proc/acpi/ibm/thermal; temperatures: 44 41 33 42 33 -128 30 -128
On some models there are three additional sensors at Embedded Controller offsets 0xC0 to 0xC2, which can be read by parsing /proc/acpi/ibm/ecdump:
# perl -ne 'm/^EC 0xc0: .(..) .(..) .(..) / or next; print hex($1)." ".hex($2)." ".hex($3)."\n"' < /proc/acpi/ibm/ecdump 40 48 43
The Active Protection System accelerometer also reports a temperature (but it is not certain that the sensor location is inside the HDAPS chip):
# cat /sys/bus/platform/drivers/hdaps/hdaps/temp1 41
Finally, the hard disk temperature can be read through the SMART interface:
# smartctl -A /dev/hda | grep Temperature 194 Temperature_Celsius 0x0022 145 097 000 Old_age Always - 31
Sensor locations
This information is model specific.
ThinkPad T43
The following image, prepared by Shmidoax, summarizes the results of his experiments using cooling spray to cool down components and observe the effect on the sensors.
(click to enlarge)
(click to enlarge)
Summary:
EC offset Index in "thermal" Location (estimated) 0x78 1 CPU 0x79 2 Between PCMCIA slot and CPU (same as HDAPS module) 0x7A 3 PCMCIA slot 0x7B 4 GPU 0x7C 5 Battery (front left) 0x7D 6 n/a 0x7E 7 Battery (rear right) 0x7F 8 n/a 0xC0 none Bus between Northbridge and DRAM 0xC1 none Southbridge (under Mini-PCI card, under touchpad) 0xC2 none Power circuitry, on underside of system board under F2 key
ThinkPad T40
The location of one of the sensors is identified here.
EC offset Index in "thermal" Location (estimated) 0x78 1 CPU 0x79 2 System board under rear left corner of Mini-PCI module 0x7A 3 ? 0x7B 4 GPU 0x7C 5 Battery 0x7D 6 n/a 0x7E 7 Battery 0x7F 8 n/a 0xC0 none n/a 0xC1 none n/a 0xC2 none n/a
ThinkPad R51
The ibm-acpi documentation includes the report by Thomas Gruber:
EC offset Index in "thermal" Location (estimated) 0x78 1 CPU 0x79 2 Mini-PCI 0x7A 3 HDD 0x7B 4 GPU 0x7C 5 Battery 0x7D 6 n/a 0x7E 7 Battery 0x7F 8 n/a 0xC0 none ? 0xC1 none ? 0xC2 none ?
