PC Engines APU - Front Panel LEDs?

Hi all! I’ve recently installed ipfire on a PC Engines APU4D4, and it works a treat.

One thing that’s puzzling me, and I haven’t found documented anywhere, is this:

What are the three front panel LEDs on the APU board used for?

I found a reference in the Core 139 release notes that said:

PC Engines APU LEDs are now controlled using the ACPI subsystem which is made possible using the latest BIOS version

…but can’t find any other mention of it.

Appreciate any pointers!


Look at this link, https://github.com/opnsense/core/issues/2114 last entry by soder10 (Apr 4)
Not sure if this might help …

On a first quick search i found at old forum a entry in the German area. So i dont want post the link as reference. But @arne_f answered there the question what the led does from the apu in english description.

LED1 CPU Heartbeat
LED2 RED Recieve

Hope this helps.

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Thank you both! Paul’s link lead me to here:


…which in turn lead me to discover:

/sys/class/leds/apu4:green:led1, 2, and 3 directories on the system.

The “trigger” file in those suggested they were activated by “heartbeat” and “netdev” activity, and the “device_name” and “mode” files in led2 and 3 suggested RED0 RX and TX activity.

This lines up exactly with what Tulpenknicker found in the old German forums, so I believe that’s the answer.

It appears with some tinkering that these could be configured to indicate other things, but for now it’s quite satisfying just to know what they mean out of the box! Thanks again.

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