I've got an external micro SD card that I am connecting via USB to my phone for dashcam recording. However, I have noticed an annoying issue - if I start recording before I start the car, sometimes the recording winds up going to internal flash, which is not what I want.

Obviously I have to use a wireless charger since I have a storage connected to the USB. The wireless charger is connected to the vehicle's USB power. What I see happen is that after starting the car, it takes a few seconds until USB power turns on. At that point, if I have the screen on and my notifications pulled down, I see the USB drive being ejected - the "do not remove" message shows briefly, and then the USB notification disappears. Then after a couple second, the USB re-appears and gets re-mounted. But due to the USB being ejected, the app I am using as the dashcam apparently detects that the drive is not available, and so starts recording to internal flash instead.

It's rather a hassle to have to start the car, then wait 15 seconds or so, then fiddle around with my phone to make sure the app still knows the correct location to record to. This wastes at least a minute of idling. I would rather figure out why Android thinks it should eject the drive when power is applied, and fix that instead. I have been able to reproduce the issue on my desk (wireless) charger as well, and it seems is always happens on the first power event after the USB drive is plugged in; subsequent power events have no effect.

Why is Android ejecting my USB flash drive (despite remounting a few seconds later) when I connect to power, and how can I make it stop doing this?

  • I would assume that this is a bug of software or hardware level. It is rather difficult to guess if this is an Android (AOSP) bug or a specific bug of your device, introduced by the manufacturer of the device. BTW: Please never ask a question here without mentioning the concrete device unless you are running an 100% pure AOSP system... – Robert Jan 24 at 19:34
  • @Robert Thanks for the pointer - I've added a tag for my phone model. I would assume that a phone from the creator of Android itself would be as close to "AOSP" (only adding the Google apps) as any off the shelf phone. :-) – Michael Jan 25 at 16:19
  • @Michael OEMs make a lot of changes to AOSP code particularly related to hardware. Wireless charging and USB both are vendor specific things as they won't work without vendor's binary blobs as well as necessary changes to kernel. So, as Robert said, this seems to be a bug in interaction between wireless charging and USB charging mechanism. Or something similar, can't be more specific without looking at source code in depth. You may try asking Google directly. Or have a look at kernel log and logcat soon after the problem occurs. – Irfan Latif Jan 25 at 19:01

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