Thermal Sensors
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This page summarizes known information about the locations and properties of thermal sensors on ThinkPad laptops. |
Accessing the sensors
Basic ACPI system temperature sensors
The primary means of accessing the thermal sensors is through the ibm-acpi module. When the module is loaded, the first 8 sensors (some of which may be inactive) are shown in /proc/acpi/ibm/thermal:
# cat /proc/acpi/ibm/thermaltemperatures: 44 41 33 42 33 -128 30 -128
A value of -128 (i.e., 0x80 hex) means the sensor is not connected. For example, above the two -128 values belong to the UltraBay battery, which is not plugged in.
Extra ACPI system temperature sensors
On recent ThinkPad models, three extra sensors are accessible through ACPI at Embedded Controller offsets 0xC0 to 0xC2. There are two ways to access them:
Accessing the extra ACPI sensors through ecdump
Load ibm-acpi with the experimental=1 option, and parse /proc/acpi/ibm/ecdump:
# perl -ne 'm/^EC 0xc0: .(..) .(..) .(..) / or next; print hex($1)." ".hex($2)." ".hex($3)."\n"' < /proc/acpi/ibm/ecdump40 48 43
Future models might provide additional extra sensors beyond those three. To see all candidates:
# perl -ne 'print join(" ",map(hex,m/\w+/g))."\n" if s/^EC 0xc0://' < /proc/acpi/ibm/ecdump40 48 43 128 128 128 128 128 0 0 0 0 0 0 0 0
Patch for accessing the extra ACPI sensors through thermal
To make the extra 3 sensors show up on /proc/acpi/ibm/thermal just like the 8 basic sensors, apply the ibm_acpi-extra-thermal.patch (download) kernel patch to ibm-acpi.
Then:
# cat /proc/acpi/ibm/thermaltemperatures: 44 41 33 42 33 -128 30 -128 40 48 43
If you apply this patch in conjunction with tp-fancontrol, you'll need tp-fancontrol 0.2.9 or newer.
HDAPS temperature sensor
The Active Protection System accelerometer also reports a temperature, which is identical to one of the ACPI sensors. The corresponding sensor is actually not inside the HDAPS chip, but fairly close.
# cat /sys/bus/platform/drivers/hdaps/hdaps/temp141
Harddisks SMART temperature sensor
The system hard disk temperature can be read through the disk's SMART interface:
# smartctl -A /dev/hda | grep Temperature194 Temperature_Celsius 0x0022 145 097 000 Old_age Always - 31
Or, for SATA-equipped models running a recent Linux kernel (see Problems with SATA and Linux):
# smartctl -A -d ata /dev/sda | grep Temperature194 Temperature_Celsius 0x0022 145 097 000 Old_age Always - 31
When the UltraBay Slim HDD Adapter or UltraBay Slim SATA HDD Adapter are used, the second hard disk will typically provide another temperature readout via its SMART interface, analogously to the above.
Reading this sensor will typically cause a drive spin-up and head unload.
Hitachi harddisks SENSE CONDITION temperature sensor
Recent Hitachi disks provide a non-standard SENSE CONDITION command which reads the disk temperature without causing a spin-up or head unload. The reported value is the same as when using SMART. This can be invoked, e.g., using # hdparm -H, or the relevant code in tp-fancontrol (download). When using the libata driver, this requires kernel >= 2.6.19-rc1.
Utilities for viewing temperatures
The following utilities display the ThinkPad-specific thermal sensor readouts:
- The above shell commands.
- The "Sensors" builtin of GKrellM can show 6 specific ACPI sensors (out of up to 11).
- CPU Info is a KDE applet that can display the 8 first ACPI sensors as well as the HDAPS sensor.
- IBMDoK, another KDE applet. Shows 4 specific sensors (out of up to 11). So far only tested at the T60.
- IBM ACPI applet is a small gnome panel applet which shows the fan speed and thermal informations.
- There is an ibm_acpi plugin for Munin.
- GNOME Sensors Applet supports ibm_acpi.
Sensor locations
This information is model specific.
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 System battery 0x7D 6 UltraBay battery 0x7E 7 System battery 0x7F 8 UltraBay battery 0xC0 none ? 0xC1 none ? 0xC2 none ?
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 T43, T43p
Found by Shmidoax using cooling spray to cool down components and observe the effect on the sensors.
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 System battery (front left = charging circuit) 0x7D 6 UltraBay battery? 0x7E 7 System battery (rear right) 0x7F 8 UltraBay battery? 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
| Photos (click to see full size) |
ThinkPad T60
Found by Marco Kraus for use in IBMDok.
EC offset Index in "thermal" Location (estimated) 0x78 1 CPU 0 0x79 2 HDD 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 ?
The CPU thermal sensors seem to be exposed in both /proc/acpi/thermal_zone/THM0/temperature and /proc/acpi/thermal_zone/THM1/temperature, though the latter curiously seems to exist only in this file and nowhere in /proc/acpi/ibm/ecdump.
ThinkPad A31
Found by Milos Popovic using cooling spray to cool down components on a completely removed, running motherboard, to locate the sensors. Also reported here.
EC offset Index in "thermal" Location (estimated)
0x78 1 CPU
0x79 2 Battery (this one heats up when on battery power)
0x7A 3 Power (sensor near power diodes and CPU; heats up when high power consumption, has crosstalk from CPU)
0x7B 4 Ultrabay 2000 battery?
0x7C 5 Northbridge (sensor next to Northbridge, also somewhat near GPU)
0x7D 6 PCMCIA/ambient (sensor is a National Semiconductor LM75 Digital Temperature Sensor/Thermal Watchdog chip
next to the 9-pin VGA connector; sits right under PCMCIA slots but doesn't touch)
0x7E 7 Battery (this one stays near ambient temperature, even when on battery power)
0x7F 8 Ultrabay 2000 battery?
0xC0 none zero
0xC1 none zero
0xC2 none zero
The following photos (resolution reduced for server space) show the locations found for the listed temperature sensors.
| Photos (click to see full size) |
On this A31 systemboard (FRU 26P8398), there is a Maxim MAX1668 5-channel remote/local temperature sensor (4 remote + 1 self temperature) on top of the systemboard, and a National Semiconductor LM75 single-channel "digital temperature sensor and thermal watchdog" chip. It would appear that the LM75 has the ability to hard shutdown the processor (without software intervention) if its temperature exceeds a given threshold. I'm not sure if it is wired for this, nor whether the Thinkpad changes the threshold temperature from the chip's power-up default of 80°C. A software application with drivers on the LM75 webpage is available that claims to allow direct access to the thermal sensor chip (this hasn't been tried, but could be useful in other models to determine if this sensor is somewhere on the MB, and which register it corresponds to). The MAX1668's self-temperature reading does not appear anywhere in the above temperature registers; it's not clear whether it is read at all, and whether it is to be found elsewhere in the EC memory. These two chips (LM75 and MAX1668) account for some of the sensors.
