Jason_25
Posts: 120
Joined: Tue Oct 20, 2015 6:25 pm

Pi 4 negative over_voltage appears to cause more heating not less

Sat Jul 20, 2019 6:29 pm

In an effort to cool my Pi 4 down enough to eventually be put into a bag or pocket I have tried the undervolting options. This does not cause the CPU to cool down at all and may even heat it up. It is hard to tell if the extra heat comes from the negative being ignored or the reboots which build heat. I had it down to -10 and the CPU was only getting hotter. I am worried about trying it further now. Extra core voltage + overheating is not good. I know that some things have not been implemented on the Pi 4 like hdmi blanking so I was thinking it could be that also. Has anyone else tried this?

jdb
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Re: Pi 4 negative over_voltage appears to cause more heating not less

Sat Jul 20, 2019 7:59 pm

There was a bug in the NOOBS release image that caused integer wraparound if you specified a negative over_voltage parameter (and hence instead applied maximum over_voltage). Do a sudo apt-get update && sudo apt-get upgrade to get a firmware that has the fix.
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Jason_25
Posts: 120
Joined: Tue Oct 20, 2015 6:25 pm

Re: Pi 4 negative over_voltage appears to cause more heating not less

Sat Jul 20, 2019 10:26 pm

Thanks for that information.

I am running Devuan Stretch 32-bit with the 20190709 bootloader and kernel from raspberrypi.org. It looks like the boot firmware included in raspberrypi-bootloader is also from 7/9. These are the latest files available on the web site. I browsed the commits to the firmware on github and did not see anything about what you mentioned so I don't know If I am on the right track or not.

jamesh
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Re: Pi 4 negative over_voltage appears to cause more heating not less

Sun Jul 21, 2019 2:45 pm

Jason_25 wrote:
Sat Jul 20, 2019 10:26 pm
Thanks for that information.

I am running Devuan Stretch 32-bit with the 20190709 bootloader and kernel from raspberrypi.org. It looks like the boot firmware included in raspberrypi-bootloader is also from 7/9. These are the latest files available on the web site. I browsed the commits to the firmware on github and did not see anything about what you mentioned so I don't know If I am on the right track or not.
You need to talk to Devuan team, it's their distribution, so they need to fix it.

Or just use Raspbian. It's better.
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Jason_25
Posts: 120
Joined: Tue Oct 20, 2015 6:25 pm

Re: Pi 4 negative over_voltage appears to cause more heating not less

Mon Jul 22, 2019 4:19 pm

I tried Raspbian first thing. It has this weird problem where the screen is not refreshed until you move the mouse. It also has a DE that does not look very touch screen friendly: you want to be able to easily force-resize windows to deal with the low resolution and make the window controls larger so you can touch them easier.

Devuan does not support the Pi 4. In situations where a Pi is supported I have found their support to be excellent. So I made my own distribution because Raspbian was broken. It generally works fine so I guess I succeeded?

By using the newer kernel with an older Debian-based distribution I can use KDE 4 instead of KDE 5 which saves some memory.

I have not even confirmed that the problem exists in my case. Repeated reboots could be causing the perceived heat build up. As I commented before, the commits on Github make no mention of any fixes for this kind of problem. Furthermore, there is no mention of this problem anywhere else after searching on Google.

For now I can only conclude that negative over_voltage values do not work well. Another explanation is that heat build up could be coming from a combination of areas on the board, not just the CPU. Since the major areas on the board are thermally connected this could tend to heat up the CPU and adjusting Vcore would have little effect.

jdb
Raspberry Pi Engineer & Forum Moderator
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Re: Pi 4 negative over_voltage appears to cause more heating not less

Mon Jul 22, 2019 4:23 pm

Hang on, are you assuming that the setting is broken without measuring things?

Run vcgencmd measure_volts in both cases - default volts and undervolted. This will directly confirm that the setting has had an effect.
Rockets are loud.
https://astro-pi.org

Jason_25
Posts: 120
Joined: Tue Oct 20, 2015 6:25 pm

Re: Pi 4 negative over_voltage appears to cause more heating not less

Wed Jul 24, 2019 4:25 pm

I investigated the voltage problem further and I found out the problem with Raspbian.

I think the problem with Raspbian screen refresh and HDMI failures is because the new driver does not work with screen rotation in config.txt. It instead uses "randr" like a regular PC. So you wait to boot into xorg before changing the screen rotation.

I had to install libraspberrypi-bin which itself depended on libraspberrypi0 from the website and device-tree-compiler from the repositories. The "integer wrap around" does happen when specifying greater than -9. I could kind of see how that could happen. Here is a small chart of the voltage results.
stock: .8578v
-1: .8349v
-5: .8279 or .8332
-10: 1.1+!!!
-9: .8314 or .8261
As you can see this device won the silicon lottery because it did not fry at high voltage and seems to run stable at -9. I see that there is a newer kernel and firmware than 7/9 which is what I am using but -9 undervolt is good enough for me right now. The temperature has come down about 3c or so.

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