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Disabling GSM modem drains the battery on N7100

Added by Dmitriy Dmitriev 11 days ago

After installing Replicant 6.0-0004-rc3 on my N7100, I disabled the modem by renaming "/system/lib/libsamsung-ril.so", and enabled airplane mode as well (which was redundant though). After some time, I noticed that the Battery usage stats showed that nearly a half of the power was drained by the cellular module, which was supposed to be disabled (IMEI wasn't shown in the "Phone status" section). I also started experiencing some system crashes a few times per day. The device would just reboot all of a sudden. Then I renamed the file back to "libsamsung-ril.so" and reset battery stats keeping airplane mode on. The cellular module item never appeared on the list since that point.
I suppose this might be not just a power consumption problem, but also a security/privacy issue.


Replies (3)

RE: Disabling GSM modem drains the battery on N7100 - Added by Denis 'GNUtoo' Carikli 11 days ago

After installing Replicant 6.0-0004-rc3 on my N7100, I disabled the modem by renaming "/system/lib/libsamsung-ril.so", and enabled airplane mode as well (which was redundant though).

It's not really redundant, both do different things.

Airplane mode just tells the modem not to go in full power mode, so it's not supposed to transmit but it's still running.

So when you will re-enable the modem by renaming libsamsung-ril.so, it will stay in low power mode once booted.

Also updating an image obviously gets rid of the rename so it's not a bad idea to do that to be safer.

After some time, I noticed that the Battery usage stats showed that nearly a half of the power was drained by the cellular module, which was supposed to be disabled (IMEI wasn't shown in the "Phone status" section).

What happens is that if you move libsamsung-ril.so, the system will not load the modem firmware inside the modem, but the chip could also still be on. Replicant could also be retrying to several times and too frequently to find libsamsung-ril.so.

I also started experiencing some system crashes a few times per day. The device would just reboot all of a sudden. Then I renamed the file back to "libsamsung-ril.so" and reset battery stats keeping airplane mode on.

The crash would need to be debugged to be fixed as if it's somehow related, it could be in the kernel or in the modem stack among other things.

The cellular module item never appeared on the list since that point.

I didn't understand what you meant here.

I suppose this might be not just a power consumption problem, but also a security/privacy issue.

If disabling the modem is too inconvenient then we have an issue.

I often did it (with the new script) on a Galaxy SIII (GT-I9300) and and Galaxy SII (GT-I9100) and I didn't notice any inconveniences with the last versions of the script (which reboots the device to turn the modem off and on).

At some point we probably will need to improve the support for disabling the modem by integrating it better and directly in libsamsung-ipc and Replicant instead of using scripts.

Denis.

RE: Disabling GSM modem drains the battery on N7100 - Added by Dmitriy Dmitriev 9 days ago

Hi, Denis,

You were right about airplane mode, it wasn't completely redundant.

I didn't understand what you meant here.

I meant the system component list in battery usage stats. After I renamed the file back to libsamsung-ril.so, the 'cellular module' item disappeared from the list as it stopped cunsuming a considerable amount of power.

If disabling the modem is too inconvenient then we have an issue.

We certainly have an issue here, at least because the "disabled" cellular module drains the battery twice faster.

I'll try to reproduce this on another device when I have a chance.

RE: Disabling GSM modem drains the battery on N7100 - Added by Andrés D 2 days ago

Hi Dimitry.

I used to use Replicant 6 on an i9300 without a SIM card and the battery drained faster than with a SIM inserted. I don't know if it's related.

Andrés

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