p-paul
Posts: 11
Joined: Wed Jun 16, 2021 12:08 pm

Putting individual cores to low power on Pi4B

Wed Jun 16, 2021 12:28 pm

Dear Community,

For a project I'm trying to lower power consumption of a Pi4B to potentially power it with only 500mA via a USB2 port of a computer.

  • However how could I achieve the same but with individual cores? Eg. switch all cores into low power but one?
  • From what I know a /boot/cmdline.txt maxcpus=1 normally won't do the trick as the cores still consume power.

Any hints on how to achieve this? Thanks a lot for your support!


Remark:

If I can't achieve this with the PI4B a plan b could be a 3A+/3B+, but it seems the PI4B is the better choice regarding low power (viewtopic.php?t=257144#p1568134).
A zero wouldn't fit the project.

p-paul
Posts: 11
Joined: Wed Jun 16, 2021 12:08 pm

Re: Putting individual cores to low power on Pi4B

Thu Jun 17, 2021 7:45 pm

Of course, if this only can be achieved using a different distribution than Raspberry Pi OS, that would be completely fine for my project.

trejan
Posts: 3321
Joined: Tue Jul 02, 2019 2:28 pm

Re: Putting individual cores to low power on Pi4B

Thu Jun 17, 2021 7:53 pm

p-paul wrote:
Wed Jun 16, 2021 12:28 pm
However how could I achieve the same but with individual cores? Eg. switch all cores into low power but one?
AFAIK you can't. The low power mode you're talking about is when the VPU is still running but the ARM cores are all turned off. I don't think the power gating is capable of selectively turning on/off individual cores.

timg236
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 872
Joined: Thu Jun 21, 2018 4:30 pm

Re: Putting individual cores to low power on Pi4B

Thu Jun 17, 2021 8:01 pm

POWER_OFF_ON_HALT=1 turns off the PMIC outputs at HALT so the entire SOC is powered off.

There's no way to turn off individual CPU cores on 2711, however, the clock gating is pretty good so AFAIK it makes little difference to idle power consumption.

500ma is quite optimistic and I think you are likely to see crashes as soon as the system does anything. maxcpus=1 might limit the power spikes under load. HDMI and USB will consume extra power but you might just get a headless system working.

You could try setting the following config.txt options to limit clock speeds.
core_freq=200
arm_freq=600

timg236
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 872
Joined: Thu Jun 21, 2018 4:30 pm

Re: Putting individual cores to low power on Pi4B

Fri Jun 18, 2021 8:09 am


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