TideLog Posts Tagged “reboot”

I had this problem suddenly pop up on me. My 3GS is jailbroken on iOS 5.01, it was all perfect until about two weeks ago. Every time I fully switch the phone off and then on again either using the power switch or because the battery went flat, with just WiFi and the cellular active, the phone would constantly crash at the home screen after two minutes, and reboot. It didn’t matter if I logged in using my passcode, or left it sat at the passcode screen, it still did it. If I was quick enough to log in using my passcode and launch an app, it still rebooted while the app was starting or running. The funny thing was, if I left it, it would stop the reboot cycle after about 20 or 30 reboots, and I could use it as normal, until it was fully powered off again, then the whole dance started again.

This whole thing is bad for the phone, as it’ll be constantly thrashing the flash chip, as it always does disk checks on sudden resets (you’ll know when it’s doing a disk check as the Apple logo stays on for AGES, it HASN’T crashed, leave it, it will continue, if you have a lot of data and apps it’ll take a while), this will run the chip into the ground if not put right, and you’ll lose all your data and settings if you don’t use iCloud backup. I don’t care about the phone, it can be replaced, but data can’t, so I always keep my phone backed up via iCloud. All I have to do is have it plugged in and connected to WiFi at night while I sleep, with the phone in sleep, and it backs up automatically.

I delved into the system logs, and there were a ton of kernel panic logs, all within three minutes of each other, for all 20 times it had rebooted, all with “WDT timeout” errors in. Now I’m going to get a little technical to explain what WDT is. It stands for WatchDog Timer, and all processors have them, they can also be software, as part of an OS. It monitors system processes, and internal chip functions, so for example if a computer CPU isn’t functioning or one of its subsystems isn’t working (the floating point unit isn’t working, not responding correctly, or reports a fault, for example), the watchdog timer pulls a reset on the CPU and motherboard circuitry by pulling the resistance on a reset pin of the processor high, resetting the device completely including all subsystem circuitry. You cannot reset a CPU without the whole system being rebooted, the motherboard components would be put into an unstable state, software would crash, and can actually allow exploits!

So, I did a bit of playing around with my phone, and I actually switched Airplane mode on, also turning Wi-Fi off. I rebooted, and the problem STOPPED! I switched just WiFi on and the phone stayed on. The trouble was I couldn’t use the phone, if I disabled Airplane mode fully it would reset again. So I had narrowed the fault down to the cellular section. The next phase was troubleshooting whether it was hardware or software, so because I have regular iCloud backups, I went into Settings-General-Reset-Reset all settings.

DO NOT, and I repeat, DO NOT, use the Reset All Data & Settings option when Jailbroken, it will brick your phone and you’ll need to do a DFU reset, if you have no recent backups you WILL lose data. Using the Reset Settings Only option is SAFE, I have used it on customer phones many times.

My phone is now settings reset, and seems to be staying on, it is in the middle of restoring apps, messages, contacts and data…. The thing that makes me feel good as a phone repairer is I did it all on my own, no forums or Apple “Genius”es needed, we all know what clowns they are 😉

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