Optimize Radxa Zero Power Consumption on Linux (Goal <2.5W)

#1

Hi guys,

I want to run some tests how low I can get the power consumption on the Radxa Zero. My goal would be to power it from a 500mA USB 2.0 port (2.5W), ideally even with Wifi. In my application I don’t need HDMI and GPU.

*How can I disable cores. I assume maxcpus=1 would do the trick?
*How can I limit the max frequency of the cores?
*Is there a way to limit the power consumption of the GPU? (Maybe this is even not necessary if the GPU automatically enters a very low power mode when unused)
*Can the HDMI be disabled?
*Any other ideas to limit the power consumption are welcome of course

Thanks a lot for your help! Can’t wait to run the first power measurements.

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#2

To archive your goal:

Step1: connect the zero to you usb2 port
Step2: do not connect usb devices, do not run games
Step3: goal archived :100:

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#3

Hi @jack,

thanks a lot for the quick reply!
Coming from the BCM2711 that seems much easier than I thought :slight_smile:
Do you think I might get issues with the current spikes from Wifi TX when powering it only with 500mA, as the current spikes of the BCM43455 can be up to 400mA (https://www.cypress.com/file/298786/download)? I can add some capacitors though.

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#4

So you think I will be able to power the Radxa Zero over usb ? Planning to connect the zero to a Apple Airport Extreme (A1521) router with a single USB 2.0 port. No other peripherals will be connected to the zero, except using the WiFi of course.

Can’t find specs on the USB 2.0 port on the Apple router but I guess its a standard 5V 500mA. It’s not a dealbreaker, I can also use an iPad charger to drive the zero I guess.

#5

I guess its possible to underclock and write a custom DTS as you would OC.
Also you might be able to disable the wifi as guess in dongle model you don’t need.

Running on a 2.5watt USB2 with a 5 watt TDP device is likely to always be hit and miss depending on load even thought the 5 watt TDP is likely a theoretical max.

I got confused with the eMMC images whilst using USB for power as they didn’t boot until on a 2amp 5v charger.
Maybe there is a parasitic leak from the hdmi as when connected the green LED flickers dimly and it doesn’t power cycle as strange it seemed to prefer the charger to what was a USB 3 that flashed the eMMC.

[edit]
You can not take that for gospel as have struggled to get it to boot and that was how I got it to boot as sure I did the exact same before but it didn’t and only change was to swap from usb to charger.
I guess if someone created a opp table where 1.4Ghz of the Pi3 was the max the opp volts could drop considerably and maybe a underclocked version will be likely maybe also with functions to disable hdmi as expecting it could run very lightly being it is a 12nm Soc as opposed to 22nm?

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#6

I wonder… should one of those infamous USB Y cables (similar to this one) suffice?

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#7

If you can draw 500mA from each port, for sure it would work (assuming that Zero doesn’t draw more than 1amp).