Ancestors

Written by Manawyrm | Sarah on 2024-09-01 at 21:22

New blog post:

Executing Linux applications on a Raspberry Pi in less than 3.5s from power-up! 🚀🏎️

(and other power saving tricks)

https://kittenlabs.de/blog/2024/09/01/extreme-pi-boot-optimization/

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Written by Graham Sutherland / Polynomial on 2024-09-01 at 22:49

@manawyrm something worth trying is dropping the 5V supply voltage for the Pi down to 4V. the limited schematics available show the board using PAM2306 and RT8088 buck regulators to derive the 3.3V and VDD_CORE voltage rails. the PAM2306 goes from 60% efficient at 5V up to 85% efficient at 4V in, which is a major increase. the RT8088 gains a couple of percent efficiency by dropping to 4V too.

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Written by Manawyrm | Sarah on 2024-09-01 at 22:52

@gsuberland Uhhh! Interesting! That should be easy to test, thanks.

Not sure what the camera module thinks of this, but I‘ll give it a shot!

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Written by Graham Sutherland / Polynomial on 2024-09-01 at 22:53

@manawyrm according to the schematic I'm looking at, the camera port runs 3.3V, so you'll be saving power there too.

https://datasheets.raspberrypi.com/rpizero2/raspberry-pi-zero-2-w-reduced-schematics.pdf

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Toot

Written by Manawyrm | Sarah on 2024-09-01 at 22:53

@gsuberland Huh!! Thanks 😻

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Descendants

Written by Graham Sutherland / Polynomial on 2024-09-01 at 22:56

@manawyrm I don't know where else the 5V rails go on the board since I don't have the rest of the schematic, but based on how they've named the power nets it's a pretty reasonable guess that the only other usage of the 5V rail is for the USB ports, and since you're disabling those anyway you should be fine. the 5V_CORE is almost certainly a filtered power domain used only for the RT8088.

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Written by Timon 🛠 on 2024-09-01 at 23:01

Yea, like 99% certain 5V only powers the regulators and the USB ports.

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Written by Timon 🛠 on 2024-09-01 at 23:04

Ah its a zero, yea then def. nothing critical. On Pi5 I'm not as certain with RP1.

HDMI also needs the 5V for the EDID but that will be fine at 4V too.

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Written by Graham Sutherland / Polynomial on 2024-09-01 at 23:09

@timonsku EDID is also disabled here so it sounds like we're golden

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Written by Graham Sutherland / Polynomial on 2024-09-01 at 23:08

@timonsku @manawyrm nice.

I think technically the efficiency peaks at about 3.6V but at that point you drop down into the lower range of the RT8088's current delivery capabilities, which might glitch the core voltage rail out during high load.

if it's not obviously unstable at 4V I'd maybe try 3.8V and stress test it. writing a script that goes from 0% load to 100% load and back repeatedly, alternating pure CPU and memory bound loads, is a great way to check for voltage regulation stability.

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Written by Manawyrm | Sarah on 2024-09-01 at 23:13

@gsuberland @timonsku with the final device being outdoors in anything between -20°C and +70°C weather I‘m a bit concerned about any sorts of overclocking or operating outside of regular operating parameters. Efficiency is nice, but compromising reliability for that isn‘t worth it (at least in this application)

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Written by Graham Sutherland / Polynomial on 2024-09-01 at 23:24

@manawyrm @timonsku away from my desktop at the moment but I can check the datasheets to see what the derating is on current delivery and efficiency. it should be fine at 4V though.

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Written by Graham Sutherland / Polynomial on 2024-09-02 at 00:40

@manawyrm @timonsku just checked. they all look pretty stable in that temperature range. you get some switching frequency drift but that shouldn't be an issue.

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Written by Graham Sutherland / Polynomial on 2024-09-02 at 00:48

@manawyrm @timonsku also since the efficiency is going up by a solid 15% you'll probably be seeing lower temps on the buck ICs anyway.

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