[FAQ] TDA4VM: How to read on-die temperatures on J7 family of SoCs using Linux

Hi,

J7 Family of SoCs have multiple on-die sensors to read the SoC temperatures on various domains.
They are part of the VTM module. VTM stands for voltage thermal management module.

All the sensors are essentially doing the ADC conversions to read out the temperature & give out a digital
value & we use polynomial equations to generate a look up table for ADC value Vs temperature & vice versa.

For example on J721e/TDA4VM:

On the Linux SDK: https://www.ti.com/tool/download/PROCESSOR-SDK-LINUX-J721E

We need add 2 patches on top to get the temperature reading using Linux.

1. Patch to add device tree nodes for the VTM module.
2. The VTM temperature sensor driver patch.

Below is the table with the zip of patches for multiple Linux SDK versions of J721e & J7200. This will updated as and when we have newer SDKs & newer J7 SoC family devices.

Steps to add the patches, build & copy the updated images to SD card:

Download the specific SDK/SOC zip file that is required & rename it as vtm.zip
Unzip the vtm.zip to the $PSDK_Linux/board-support/linux-* folder
cd $PSDK_PATH/board-support/linux-*
git am vtm/*
cd ../..
make linux


Insert the Linux SDK SD card.

Edit the file $PSDK_PATH/Rules.make
Set DESTDIR=/media/$USER/rootfs
cd $PSDK_PATH
sudo make linux_install

Upon booting Linux with the updated Images We can read temperatures using:

cat /sys/class/thermal/thermal_zone*/temp

Best Regards,
Keerthy