NimbUx
Posts: 108
Joined: Fri Jan 03, 2020 10:33 am

minimum voltage (arm) ?

Tue Feb 25, 2020 2:33 pm

Just curious, the base arm voltage is (reported as) 0.80125 without special over_voltage set.
Is this the nominal (or close) volts specified for the Pi4 SoC ?
Is this base voltage also a hard minimum, or else will the Arm tolerate some amount of
under_voltage (aka "negative" over_voltage), and if it will : then how do you specify it ? Might be usefull when also under-clocking.

jahboater
Posts: 5194
Joined: Wed Feb 04, 2015 6:38 pm
Location: West Dorset

Re: minimum voltage (arm) ?

Tue Feb 25, 2020 2:36 pm

NimbUx wrote:
Tue Feb 25, 2020 2:33 pm
Just curious, the base arm voltage is (reported as) 0.80125 without special over_voltage set.
Is this the nominal (or close) volts specified for the Pi4 SoC ?
Is this base voltage also a hard minimum, or else will the Arm tolerate some amount of
under_voltage (aka "negative" over_voltage), and if it willn how do you specify it ? Might be usefull when also under-clocking.
One of my Pi's (a Pi Zero acting as a digital clock) runs with "over_voltage=-4" in /boot/config.txt to save power.

On the Pi4 it seems to be ignored, probably because the new DVFS firmware knows better.
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NimbUx
Posts: 108
Joined: Fri Jan 03, 2020 10:33 am

Re: minimum voltage (arm) ?

Tue Feb 25, 2020 2:54 pm

jahboater wrote:
Tue Feb 25, 2020 2:36 pm
On the Pi4 it seems to be ignored, probably because the new DVFS firmware knows better.
Negative values appear ignored indeed. Interesting that you put the DVFS in question : I seem to remember there to be a way to switch the DVFS off on a per-boot basis, like, pressing (or relasing ?) shift during the boot, but how precisely and when to assert it during system start had not been clear.
Someone could certainly enligthen me in this respect ?

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