[Nut-upsuser] Weekend Puzzle: computer posing as an UPS

[Jim Klimov]

Follow-up:

* Powering the Raspberry Pi5 from an USB-C port wired on the motherboard
was much more promising, it survived over 8 hours building NUT in a loop
(in a tmpfs). And in the morning I found it turned off (red light on the
Pi).

* Per
https://stackoverflow.com/questions/4702216/controlling-a-usb-power-supply-on-off-with-linux
it seems not possible to programmatically truly power-cycle USB port/hub,
as 5V pins are "always on"; and per
https://stackoverflow.com/a/16316401/4715872 - at least not on MoBo ports
(some hubs may have invested into being fully up to spec and control power
fully). The referenced uhubctl <https://github.com/mvp/uhubctl> on my PC
said "No compatible devices detected!" so I guess that's it.

* Whatever I could find with (suggestions welcome) `grep -r . `find
 /sys/devices/pci0000\:00 -name '*usb*port*'` /sys/bus/usb/devices/` did
not expose any differences beside timestamps with the RPi5 plugged and off,
unplugged, and plugged back in again (with auto-boot). I hoped for some
power draw statistics to at least learn which port it lives on, to try
managing that somehow.

* Overall, housing the Pi inside a cooled and somewhat dust-protected PC
case seems a neat idea, but for powering the Pi, it seems I would need to
use a real wall-power adapter (as noted many times on the net, ideally
Raspberry's own one as others tend to vary in actual voltage provided under
load).

* But before that, I'm thinking if I could tap into the ATX power supply
though (using "HDD" or "FDD" plugs) or fan sockets (could be individually
manageable? gotta exempt one from OS/HW temperature-based mgmt then).

Did anyone trod these side paths yet, any learnings? :D

Jim







On Fri, Sep 27, 2024 at 4:43 PM Jim Klimov <jimklimov+nut at gmail.com> wrote:

> FWIW, a few lessons learned:
>
> * Different USB-A sized ports (even if marked USB-3.2) did not prove a
> stable source, with Pi5 occasionally turning off or rebooting. Sort of
> behaved well for days, but as soon as I added load like package installs or
> NUT builds, it did not survive 5 minutes...
>
> * Might be the MoBo turning off or cycling the port due to "overload"?..
>
> * Tried the `usb_resetter` script (referenced in NUT contribs) and host
> `dmesg` did show re-detection of keyboard etc., but a turned-off Pi did not
> boot up. Did not check much further, but did harbor hopes that a funny NUT
> driver could "shutdown/reboot" the USB port acting as an UPS for Pi...
>
> * The Pi power socket is dumb-USB so the host does not "see" any IDs about
> it.
>
> * Currently trying with a USB-C port on the MoBo, and a USB-C to USB-C
> cable rated for 60W -- and so far it survived a few loops of NUT fightwarn
> builds. Complains of undervoltage fairly frequently (every 30-60s), but now
> did not crash yet.
>
> Jim
>
>
> On Mon, Sep 16, 2024, 13:57 Greg Troxel via Nut-upsuser <
> nut-upsuser at alioth-lists.debian.net> wrote:
>
>> Kelly Byrd <kbyrd at memcpy.com> writes:
>>
>> > With USB-C ports and cables, there are a ton of profiles, I don't know
>> what
>> > the new Pi's support, but likely something like 3A @ 5V, 9V, or 12V over
>> > USB-C
>>
>> Up to the RPI4, I was pretty sure there wasn't PD, just 5V and it drew
>> what it drew, and you hoped that the supply was big enough.
>>
>> It seems the RPI5 will use PD if given a capable supply.  Looks like 5V
>> 5A, and it won't negotitate higher voltages.   There's an official
>> supply that does PD
>>
>>
>> https://www.newark.com/raspberry-pi/sc1153/power-supply-usb-c-5-1v-5a-white/dp/82AK3955
>>
>> and the output spec is
>>
>>   5A at 5.1V, 3A at 9V, 2.25A at 12V, 1.8A at 15V
>>
>>   looks like a TUV seal
>>
>>
>>
>> I find Jim's way of using this interesting, but my approach is totally
>> different.  First, when I'm using a Pi, it's because I want a low power
>> computer that I can leave on all the time, or can place in a different
>> physical location I don't particularly want to do things on a Pi instead
>> of a desktop.  And then I want it to be reliable.
>>
>> That leads me to plug a power supply into a UPS, or to use POE (from a
>> POE switch which is plugged into a UPS).  For RPI3, I found a POE
>> ejector that splits the POE ethernet cable into ethernet only and a
>> micro USB.
>>
>>
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