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My laptop runs Arch, and I can find battery information about the battery of the laptop inside /sys/class/power_supply/BAT0. As far as I know, I have installed nothing to make this information available. I would love to have the same information available on my Jetson AGX Xavier, which is run by a battery, but has no idea about the max energy, percentages, etc. I suspect there needs to be more hardware which can collect this data. What does it look like, and can I implement it myself?

user93114
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That is sysfs, a pseudo or synthetic filesystem used by the kernel to export things. It is to interact in a *nix way with the system, just like the older /proc is to interact with the kernel and its modules.

$ mount | grep sysfs
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)

You can read more here What is the difference between procfs and sysfs?

About the battery information, you will need a kernel module that can talk to a particular firmware. For example my Debian system has thinkpad_acpi kernel module loaded to make things like this happen. I can't tell much about the writing. From what I've read some firmware may present itself through some bus device (for example SMBus/I2C, maybe as a keyboard or even a mouse) to communicate with the OS. In the past I've soldered LM75A temperature sensors directly onto SMBus lines of memory DIMM's, and used I2C software and lm-sensors to read them out after fiddeling with a kernel module and settings in /proc/bus/... somewhere.

Btw. I like to point out the TLP project has tlp-stat --battery which can conveniently report on /sys/class/power_supply/ and many other power-management related things.

But you will need a 'device driver' first. If you are comfortable with Kernel C coding, you could give it a try. You would be writing the firmware and building the hardware yourself anyway, so at least no mysteries there. I don't know the Jetson, but I'd think there are some other home-brew projects like this already out there in Linux land. Maybe for the Raspberry Pi?

I was reading some 2013 and 2017 posts on ACPI on ARM and wanted to add:

These ACPI/UEFI appearantly are x86/BIOS-world things and afaics based on abstraction standards which don't really apply to the SoC/ARM world per se. And there is the issue with how vendor firmware 'blobs' fit in with 'open source efforts'. But no, I have not seen ACPI for Raspberry although some 'ACPIA' (ACPI for ARM?) efforts seem to be there.

https://lwn.net/Articles/574439/ https://forums.raspberrypi.com/viewtopic.php?t=180001

mpe
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