6by9
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 12:42 pm

bullen wrote:
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?
Eric knows very little detail of the firmware.
You've already had an answer from me, 7 years at Broadcom on VideoCore, 2 years volunteering for Pi Towers, and now a year as an employee.
Throw in an answer on github https://github.com/raspberrypi/linux/issues/2198.

It is non-trivial (several man months), and has no gains for the educational goals of the Pi Foundation.
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bullen
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 1:54 pm

@mikerr IME the zero lasts ~4 hours... that's one order of magnitude! thx for the lead though, I will follow it... I'm doing radio that needs 100% uptime at reception and cannot work with bootup latencies.
@6by9 Ok, only suspend is possible, not simply turning off the part of GPU that handles graphics? How much financial help would convince you to tackle the challenge and how far do you think you can push the savings?
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W. H. Heydt
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 4:31 pm

bullen wrote:
Sun Jan 21, 2018 1:54 pm
How much financial help would convince you to tackle the challenge and how far do you think you can push the savings?
How much money have you got? My guess is that you're looking at throwing somewhere in the range of $200K to $5 million at the project to get what you want, and that assumes that you can get the RPT to work on it at all...which is unlikely.

bullen
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 4:40 pm

That's a wide range, you want in? I would appreciate if we took the time to write out acronyms in general, and non obvious ones in particular.
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mwrich4
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 5:49 pm

bullen wrote:
Sun Jan 21, 2018 4:40 pm
That's a wide range, you want in? I would appreciate if we took the time to write out acronyms in general, and non obvious ones in particular.
(Asking for explanations of acronyms several times is odd.)

It sounds like you have a large scale project in mind. You should state your credentials and your needs clearly.

At this point, asking for research and a lengthy explanation is also VERY costly in man-hours. This forum is not really the proper channel.

Google these terms:
What is RFI and RFP?
An RFI is primarily used to gather information to help make a decision on what steps to take next. RFIs are therefore seldom the final stage and are instead often used in combination with the following: request for proposal (RFP), request for tender (RFT), and request for quotation (RFQ).

jamesh
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Re: Broadcom BCM2835 Power Saving

Sun Jan 21, 2018 5:52 pm

I'd say about $200k minimum spend, if it's deemed possible to do (it might not be)

The problem you have though is you need someone experienced with Videocore, and that's basically only the RPFT nowadays. And we are all busy on more important stuff, our roadmap is very busy for the next 3 years at least. So even if the money was there, it seems unlikely that anyone would be available to do the work.

It hasn't been done in the last 5 years of Pi, it seems unlikely it will be done in the future.

(FYI, 6 years working on VC at Broadcom, alongside 5 years volunteering for RPFT and working for them full time for 1 year)
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 12:38 am

jamesh wrote:
Sun Jan 21, 2018 5:52 pm
I'd say about $200k minimum spend, if it's deemed possible to do (it might not be)
So the low end of my SWAG was pretty good...

The high end would probably include hiring people who could reverse engineer enough of the VC4 to figure out how to do it...if it could be done at all, while being paid to do so.

I worked in a project in the early 1980s that the company in question spent $3 million on, then cancelled it. So, yeah, sometimes the answer is "not going to happen".

6by9
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 10:52 am

If you only want to scale the ARM cores back, then the min and max core frequencies for the ARM can be overridden by editing /boot/config.txt and adding

Code: Select all

arm_freq_min=100
arm_freq=300
Some experimentation would be required to see what numbers are plausible, but I don't think you'll get any huge power saving from it. You may also want to tweak the governor settings to make it kick up into the faster mode more readily.
You can look at /sys/devices/system/cpu/cpufreq/policy0/stats/time_in_state to show how much time the CPU has spent in each state, and the other files in /sys/devices/system/cpu/cpufreq/policy0 will tell you what mode the governor is in, and within what parameters.
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 11:09 am

Digging back into my memory, I seem to recall that underclocking the ARM's doesn't save a lot of power. But I am not sure if there was any real testing done on it.
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 11:52 am

bullen wrote:
Sun Jan 21, 2018 1:54 pm
@mikerr IME the zero lasts ~4 hours... that's one order of magnitude! thx for the lead though, I will follow it... I'm doing radio that needs 100% uptime at reception and cannot work with bootup latencies.

What exactly are you trying to achieve?
What has to run 100% up?
What wakeup latency is tolerable (you can't have literally zero).
Why 2600mAH limit?
What runtime, 24 hours?

Radu79
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 12:02 pm

From my testing with the Pi Zero, the board itself, when off (not sure what off means, is it just the CPU doing HLT?), it takes about 30 mA.
When idle, with USB and HDMI off, with an WiFi board on (the LED on it is on, but it is inactive) it takes about 65 mA. That's over day of work on a small phone battery. Combine with some solar power or larger battery it should be sufficient for almost all the uses except for mine (which requires up to a year on time, but it can be turned off for most of the time).

bullen
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 12:15 pm

Image

http://radiomesh.org

It is a new distributed P2P radio internet on top of LoRa with frequency hopping.

The reason for using a 2600mAh pack is it has the same dimension as the zero and it's cheap.

Volumes on DIY parts are crucial to get price down.

Always on is a requirement since every node will be relaying others data in the mesh.

I'm just looking into the future, right now I think the prototype I have will work.

Thanks for the HDMI, LED, underclocking and 3.3v tips!
Last edited by bullen on Mon Jan 22, 2018 2:00 pm, edited 1 time in total.
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Radu79
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 12:38 pm

But if you have the radio on all the time, I think your biggest worry is the radio itself, not the CPU/GPU. You need the CPU to run all the time, but even if it were off, the radio would use much more than the cpu.

That device looks big enough to put two small 50 mA solar panels on top, and they are pretty cheap.

bullen
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Re: Broadcom BCM2835 Power Saving

Mon Jan 22, 2018 12:56 pm

Much more than the CPU is a stretch, but I know it's a challenge:

Rx

LnaBoost Off, higher bands 10.8mA
LnaBoost On, higher bands 11.5mA
Lower bands 12.1mA

Tx

RFOP = +20 dBm, on PA_BOOST 120mA
RFOP = +17 dBm, on PA_BOOST 87mA
RFOP = +13 dBm, on RFO_LF/HF pin 29mA
RFOP = + 7 dBm, on RFO_LF/HF pin 20mA

In remote areas the battery will drain faster that's for sure!

The sun doesn't shine in your pocket.

http://www.hoperf.com/upload/rf/RFM95_96_97_98W.pdf
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Radu79
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Re: Broadcom BCM2835 Power Saving

Tue Jan 23, 2018 12:40 am

Those are the specs of the chip itself, but I guess the other components on the board will also eat a few mA here and there.
Anyway, assuming max TX power, you have ~130 mA while sending data (and in a mesh network that will always be the case), so it's twice the power of an idle Raspi Zero.

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Re: Broadcom BCM2835 Power Saving

Tue Jan 23, 2018 6:41 am

How are these mesh nodes to be charged?
Charging power will set your power budget. rather than battery size.

The concept doesn't seem viable to me from what you have revealed so far. I don't see how you can have wide area coverage, low connection latency and no long term stable power source.

If you could tolerate some connection latency you might get to a very low power by only listening in defined time windows and being in deep sleep between.

bullen
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Re: Broadcom BCM2835 Power Saving

Thu Mar 29, 2018 3:09 pm

This Chinese clone draws more power even with everything powered down, but then it can also turn cores back on for more performance when you are charging:

https://www.aliexpress.com/store/produc ... 74880.html

https://forum.armbian.com/topic/1614-ru ... nsumption/
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