Reading CPU Temperature and Controlling LED with C++ via sysfs

thermometer

Let’s take a quick look at an example C++ program which reads CPU temperature and controls an LED using sysfs. This example is a bit specific in that it’s only been tested on our NXP i.MX6 powered TS-4900 or TS-7970 running Yocto Linux, but the principles could be applied to other embedded systems as well. If you’re interested in the nitty gritty details about sysfs, take a look at The sysfs Filesystem by Patrick Mochel. Suffice it to say for our purposes, sysfs makes it easy for us to interact with system hardware using plain text files located in the /sys/ directory. The file to control the red LED is /sys/class/leds/red-led/brightness. The file to read the CPU temperature is /sys/class/thermal/thermal_zone0/temp. If we want to turn the red LED on, we simply write a ‘1’ to the file, and not surprisingly, writing a ‘0’ will turn it off. If you’ve booted up your TS-4900 or TS-7970, you can see this by running the shell commands:

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