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I have an stock-standard Acer Iconia A500 32G WiFi-only tablet. The screen usually turns on immediately when I press the power button.

However, it sometimes refuses to respond and I have to hold done the power button for a few seconds, then release it and hold it down for a few seconds again.

At that point, there'll be a vibration and the tablet will boot through the Acer and android screens.

My thoughts are that the first sustained button actually powers it down forcefully and the second brings it back up (but I can't be certain of this).

Does anyone know why this would happen? Are there any things I can look at on the file system to see what's going wrong.


To elaborate on the non-responsiveness issue, while in most circumstances a quick push of the power button will bring up the PIN entry screen, it doesn't do so in the problematic cases.

In those cases, the screen just remains black no matter how many times I push the power button. That's why I then have to do the long-press twice to (presumably) force shutdown and restart.

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What I understand from your post is that you are referring to a 'Immediate boot' is actually your device is in stand-by/sleep mode and pressing the power button once just wakes it up. Pressing the power button for a long time is indeed the way to force shut down the device and is present in all major smartphone. Since it restarts from beginning after that, it takes longer to come up to your home screen/lock screen. The real issue could be the unresponsiveness of your device when it is in sleep mode. Could you please elaborate more on that? –  Sameer Sharma Apr 19 '12 at 10:32
    
@Sameer, I've added the detail, hopefully that's enough but, if not, I'm happy to provide any other sort of detail. That's why I was hoping there may be a log file somewhere :-) –  paxdiablo Apr 19 '12 at 11:12
    
Do you have ADB on your PC/System? You could follow this guide and install it if you don't have it. ADB Installation. Also you would need to have USB Debugging enabled on your device, which may be a issue for you if it's not already enabled. If it is, Go to Android SDK Directory > platform-tools > ddms.bat (for windows). It should launch a Debugging monitor and you should get a log there. Check the log for any errors/warnings when you try to unlock the device. –  Sameer Sharma Apr 20 '12 at 4:46

1 Answer 1

Ahh, soft keys.

When the power button is pressed, the hardware raises an interrupt which is handled by an OS-provided interrupt handler. Part of the interrupt handling process included waking the processor from sleep. The software will then turn on the screen (if it was asleep), display a shutdown menu, or some other function depending on the OS version and any customizations added by the device manufacturer or third-party software installed by the user.

The power button also starts a counter in hardware. If the counter reaches a threshold without the power button being released, then the power circuit is invoked to turn off the device. This is done purely in hardware circuitry, independent of the OS or even firmware executed by the main processor. That's why it still works when the system is locked up (or perhaps overclocked and so unstable that the processor can't execute ANY code at all).

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