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Comment by foggywin | Hacker News Reader

Did you read the blog post? :)

"Raspberry Pi 5 consumes significantly less power, and runs significantly cooler, than Raspberry Pi 4 when running an identical workload. However, the much higher performance ceiling means that for the most intensive workloads, and in particular for pathological “power virus” workloads, peak power consumption increases to around 12W, versus 8W for Raspberry Pi 4."

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Alright so 27W with heavy peripheral draw then? But 12 W still means it'll be drawing 2.4 amps instead of 1.6 when a random process decides to 100% it. I guess we can always underclock it.

The real unanswered question is, does it finally have a damn sleep mode so it can save power when idle.

Jeff Geerling measured 1.8W idle power draw.

Based on my experience with previous Pis, I bet you’ll be able to drop that even further by turning off unused board components at boot time.

True, I've gotten Pi 4s pretty low (< 1W), disabling the LEDs, Ethernet, HDMI, and USB controller, but it's never gonna equal a proper suspend.

How did you disable the LED? I mean I can disable LEDs via /proc but not in config.txt correct?

Add

    # Disable Power LED after boot
    dtparam=pwr_led_activelow=off
    # Disable SD card activity led
    dtparam=act_led_trigger=none
    dtparam=act_led_activelow=off
    # Disable the ethernet LEDs - these are Pi4 specific values.
    # Look in the docs for the values for other Pi boards.
    dtparam=eth_led0=4
    dtparam=eth_led1=4

to /boot/config.txt

Thank you!

It appears to depend on firmware or kernel but for recent kernels (recent 6.1 or 6.2) activelow is no longer necessary [1]. It seems to work on CM4.

PS: my bad I disabled the LEDs via /sys not /proc previously:

> # for i in /sys/class/leds/*; do echo 0 > "$i/brightness"; done

[1] https://github.com/raspberrypi/firmware/issues/1742

I've had this drive me crazy.

The required lines were different between the Pi 2 and Pi 4 I was using at the time, and the documentation was not updated (or I'd found old docs).

An exercise in trial and error.

1W is honestly not that great, though. A smartphone will do 10x that out of the box, and still pling for Facebook notifications.

A smartphone has two entirely separate computers in it, the one that runs Android or iOS, and the baseband controller. The latter is built to be very power-efficient while waiting for a radio signal. It will wake up the dormant application OS computer when a push notification comes in.

The same likely can be built on top of an RPi, using, say, wake-on-LAN signaling, or some GPIO as an interrupt source. You'll have to suspend your OS while idle for a prolonged time though.

I read that the "PC style" power button allows both soft and hard shutdown, so I suppose suspend and hibernate come into the picture as well. It's mostly a matter of OS support, the firmware seems to be there.

According to Jeff Geerling the Pi 5 doesn't support suspend in firmware, altough it might be possible with an update.

> soft and hard shutdown

My reading of that was:

"soft" = trigger an orderly OS shutdown, the same as if you executed `shutdown now` on the command line.

"hard" = cut power immediately, as if you just unplugged the power cable.

> The real unanswered question is, does it finally have a damn sleep mode so it can save power when idle.

I dream of DIY'ing a laptop, and RPi looks like a great platform for prototyping that... until you realize there's just no sensible way to put it to sleep. Hibernate + aggressive boot time optimization?

You know it's funny, my current laptop has a weird firmware bug (certified Asus moment) where it refuses to go into sleep mode. If sleep is triggered by any OS it will straight up just shut down completely. I've lost some work the first few times I used it out of habit.

Eventually though it didn't turn out to be much of an issue, SSDs boot real fast these days anyway and I can just do a full power cycle.

Meanwhile I'm genuinely annoyed that my Thinkpad takes a second or two longer to wake up from sleep than my Mac ;)

Is there a way to limit the processor power so that it never exceeds a certain threshold? Because some people might be okay with slower processor if it means less power usage.

I think at least with the Pi 4, you can limit the CPU clock by editing a config file, which has a power limiting effect.

If you set the scheduler to powersave, it downclocks all cores and saves power that way.

Yes, there is a low power mode. And you're forced to use that if you startup with an "under"-powered supply.

Jeff Geerling on YT has a great in-depth review of these options in his latest video.

I read a lot of Jeff's blog, but his vlogs put me to sleep. He isn't charismatic and makes the worst jokes. People forget that a visual medium is visual. He channel is an example of great information that is ruined by the visual medium.

Can you explain their decision to recommend a 27W power supply then?

The new board supports more power hungry IO. If you want to use all of the IO available and push the new SoC then you're going to need a beefier power supply.

What happens if you use those beef options without a powerful PSU?

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