Documentation for power saving modes

I am running the aml-s905x-cc (aka le potato) board on Ubuntu 22.04

Is there any documentation addressing power management :slight_smile: ?

→ repartition of power draw by peripheral and how to shut down some peripherals (eg. USB, Sound, Video, IR, I2S …) ?
→ removing unnecessary linux modules ?
→ power impact when switching the CEC/Pin11 jumper ?

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What’s your power target? Idle the board uses about 200mA or 1W.

No specific target, consumption is indeed quite low.

I am comparing the board with a few alternatives. Since I disabled anything I was not using on the other ones, I would need to do the same to provide a fair comparison.

You can reference the schematics page to see what devices you can turn off through toggling GPIO controlled regulators for non-mandatory devices. Additionally, there are low power states that you can enter that uses very little power but you can’t do any processing when that happens and rely on select GPIO interrupts to wake the system.

@librecomputer Please can you give a couple of example commands to turn off/on devices? eg, USB, HDMI. Not every user can decode a hardware schematic!

Also, is there documentation about those “low power modes” you mention? How to enter them, the power consumption for each mode, and how to wake?

Thank you!

All board systems are controlled via GPIO regulators. The kernel has the necessary framework and will power off the regulators if the devices are not used by software. This topic (power) is too complex to describe simply and you need to have embedded system knowledge. A book on embedded systems and the ability to read schematics is recommended.

My board is using 220mA at idle (100MHz CPU) with just Ethernet, no other devices attached. However if I plug an HDMI cable in then the power consumption goes DOWN to 200mA :open_mouth: It doesn’t matter if the monitor is on/off, or what the CEC/GPIO11 jumper setting is. Remove the HDMI cable and the power consumption goes back up!

What could explain that? Thanks

HDMI and USB share the same regulator. HDMI 5V is always on as long as USB is enabled.