bullen
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Broadcom BCM2835 Power Saving

Fri Jan 19, 2018 11:37 pm

Can you make the CPU throttle down seriously (so you can have the zero run a whole day on a 2600mAh pack) without interrupting wakeup events like phone ARM CPUs can?
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W. H. Heydt
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Re: Broadcom BCM2835 Power Saving

Fri Jan 19, 2018 11:59 pm

You can turn off various things like HDMI and you can underclock a lot...those will cut the power requirements.

Question: When you say "run a whole day", how are you defining "day"? I can run a Pi0 plus a 3.5" LCD display for around 14 hours on a 4Ah powerbank. It takes around 180mA at idle (static image on screen but not really doing anything). About half of that is powering the screen (and probably most of that is the backlighting at full intensity), so that's an average "dawn to dusk day". That 4Ah would probably power just a Pi0 for 24 hours, a "full day". Your 2.6Ah battery could probably manage just a Pi0 for a full, average, daylight hours without any tweaks.

bullen
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 12:22 am

Ok, thx.

But are there no "low power" ARM settings under the hood somewhere?
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 1:54 am

bullen wrote:
Sat Jan 20, 2018 12:22 am
Ok, thx.

But are there no "low power" ARM settings under the hood somewhere?
Not that you can get at in Raspbian. You might check in the "Bare metal" forum.

bullen
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 1:44 pm

Ok, found this: viewtopic.php?f=81&t=44834

So is it linux or ARM that consumes most energy?

Writing my own hypervisor that can run Java will take a lifetime, so this is not applicable.

But what term can I search to trigger the built in ARM power saving features?
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 3:14 pm

AIUI, the problem is not the ARM side but the effect shutting it down has on the GPU . You in effect cannot start everything up correctly or something like that.
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bullen
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 3:24 pm

AIUI?

So there is a way to save energy by turning off the GPU altogether?

But raspbian craps out if you do?
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 3:41 pm

bullen wrote:
Sat Jan 20, 2018 3:24 pm
AIUI?
As I Understand It. Google is your friend (or even DuckDuckGo)
bullen wrote:
Sat Jan 20, 2018 3:24 pm
So there is a way to save energy by turning off the GPU altogether?
Yes, it's called the OFF switch :lol:
bullen wrote:
Sat Jan 20, 2018 3:24 pm
But raspbian craps out if you do?
Yes. Not surprising really.
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 3:58 pm

So there are no power saving features that ARM has on mobile phones in the SoC on the RPi?

Maybe those are not ARM specific but instead every manufacturer makes their own: Apple, Samsung etc.
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 4:32 pm

bullen wrote:
Sat Jan 20, 2018 3:58 pm
So there are no power saving features that ARM has on mobile phones in the SoC on the RPi?

Maybe those are not ARM specific but instead every manufacturer makes their own: Apple, Samsung etc.
There are power saving features, but because of the architecture of the Pi (where the GPU runs behind everything), using them causes problems. i.e. you need to save the state of the entire GPU when hibernating etc. If you are able to use power save features that don't affect things like that, then you can use them. But I am not sure there are any.

Note that the GPU is already pretty power efficient and shuts down blocks it isn't using.
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 4:47 pm

Ok, thx!

Looking forward to this one more and more: https://www.youtube.com/watch?v=Mp6znwaZ5xo
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 5:43 pm

Something to help the OP understand the situation... The SoCs on Pis are really GPUs with small ARM CPUs "bolted on". The ARM part of the chip is a very small portion of the Silicon. To take an example...the memory controller is part of the GPU. That's why the RAM limit for a Pi si 1GB. That's all the GPU can address.

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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 6:33 pm

W. H. Heydt wrote:
Sat Jan 20, 2018 5:43 pm
Something to help the OP understand the situation... The SoCs on Pis are really GPUs with small ARM CPUs "bolted on". The ARM part of the chip is a very small portion of the Silicon. To take an example...the memory controller is part of the GPU. That's why the RAM limit for a Pi si 1GB. That's all the GPU can address.

Quites so and Wikipedia is a good read:

https://en.wikipedia.org/wiki/VideoCore
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bullen
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 7:08 pm

Very cool! Thx for insight!
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Heater
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 8:08 pm

These video cores have been used in mobile phones. LIke the Symbian based Nokia models. So I assume that somewhere in the depths of the hardware there are power saving features.

Making that usable from Raspbian may not be trivial.

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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 8:12 pm

See now were getting somewhere, paging Broadcom experts!
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 8:45 pm

In the Nokia phones the VideoCore chip (BCM2763) was running as a graphics co-processor chip. The main ARM cores were on a totally different chip alongside the radio. It was quite possible to totally shut down the VideoCore chip when graphics weren't needed, and restart it when required.
On the Pi we have the ARM cores integrated into one chip without a way of keeping the ARM cores up without the GPU.

Most of the hardware blocks within VideoCore are power and clock gated, so consume very little power when not in use.
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bullen
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 9:08 pm

So how does one make sure they are not in use?
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 9:41 pm

bullen wrote:
Sat Jan 20, 2018 9:08 pm
So how does one make sure they are not in use?
You don't need to. They shut down automatically when not in use.

bullen
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Re: Broadcom BCM2835 Power Saving

Sat Jan 20, 2018 10:23 pm

Yes, but how do I know they are not in use? Is headless enough?
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mwrich4
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 7:42 am

I think the thing to remember is this: while the raspberry pi processor chip uses familiar building blocks, the design and implementation were towards the goal of making a small minimalist hobbyist computer system in a tiny space. Trade-offs were made, functionality was not the prime goal. Reducing system cost and retaining decent user interface speeds was probably a detailed compromise.

While the raspberry pi is a great hobbyist board and capable of many general tasks, it is not the best platform for developing a system where tailoring the hardware functionality is required.

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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 8:46 am

mwrich4 wrote:
Sun Jan 21, 2018 7:42 am
I think the thing to remember is this: while the raspberry pi processor chip uses familiar building blocks, the design and implementation were towards the goal of making a small minimalist hobbyist computer system in a tiny space. Trade-offs were made, functionality was not the prime goal. Reducing system cost and retaining decent user interface speeds was probably a detailed compromise.
The original Pi used an off-the-shelf chip that had also been used for Set Top boxes. There's not much reason for power saving modes in something that is going to be mains powered whenever it is in use.

The Pi2 and Pi3 use the same chip with a few minor changes and new ARM CPU cores.

Also, 99.99% of Raspberry Pi are going to be mains powered. Power saving isn't really a priority in the design, as it is already low for a mains powered system

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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 9:42 am

rpdom wrote:
Sun Jan 21, 2018 8:46 am
mwrich4 wrote:
Sun Jan 21, 2018 7:42 am
I think the thing to remember is this: while the raspberry pi processor chip uses familiar building blocks, the design and implementation were towards the goal of making a small minimalist hobbyist computer system in a tiny space. Trade-offs were made, functionality was not the prime goal. Reducing system cost and retaining decent user interface speeds was probably a detailed compromise.
The original Pi used an off-the-shelf chip that had also been used for Set Top boxes. There's not much reason for power saving modes in something that is going to be mains powered whenever it is in use.
BCM2835 was NOT designed for set top boxes. It was designed for mobile phones as a coprocessor, with the ARM core thrown in for experimentation.
It was used in one of the Roku streaming sticks, but set top boxes were not the intended market.
All the VideoCore blocks have numerous power saving techniques employed, however hooking them up to allow the ARM cores to really access them is non-trivial. Wherever the VideoCore processor (the VPU) is controlling a hardware block, then all the power and clock gating will be active.
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bullen
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 11:05 am

Ok, it seems we're not getting anywhere with this.

Can someone at RPF/Broadcom that knows how to hook the features up give us an estimate of how non trivial that would be?

Anholt maybe?
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 11:28 am

zero run a whole day on a 2600mAh pack
IME the lowest you can go to is 65mA on a pi (by [url=]turning off usb and hdmi)
viewtopic.php?f=63&t=127210

That would give 40hrs of "standby" with a 2600mAh pack. (2600 /65)
Reduce that time for active use, and non perfect capacity.

If you need lower power consumption than that, then look to using a microcontroller etc to remove/restart power as necessary
- an ATTiny can sleep for months at 5 uA and only wake up to turn the pi on or off
https://learn.sparkfun.com/tutorials/h2 ... wer-attiny
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