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Thread: Do Qt cause partial drawings if processor sleeps due to power management?

  1. #1
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    Default Do Qt cause partial drawings if processor sleeps due to power management?

    In many embedded devices, aggressive power management is practiced. The processor could try to go to sleep any time (every second for example). While processor is sleeping in power save mode, the display can remain turned on depending on the hardware implementation. User continue to view the previously drawn screen (before sleep). This gives a GUI application always running experience. Processor will come out of sleep mode when there is some network traffic, button press, or some hardware timer expires. Then it refreshes the screen again if needed.

    What if Qt was in middle of drawing something, while processor goes to sleep ? Since the display unit is on, do a user will see it partially drawn ?
    Do the double buffering in Qt framework solve this problem ? Or any locking mechanism is available in Qt to avoid the race condition of processor going to sleep and drawing on display.

    Any help in understanding the underlying mechanism is welcome.
    (I am new to graphics and Qt)

    Thanks
    Lunar M.

  2. #2
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    Default Re: Do Qt cause partial drawings if processor sleeps due to power management?

    The processor does not simply go to sleep while there are still processes executing.

    Cheers,
    _

  3. #3
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    Default Re: Do Qt cause partial drawings if processor sleeps due to power management?

    Ideally if a user is reading some message on screen, we don't need to keep the processor running. The display hardware can keep refreshing the last drawn image for the user. The processor need to wake up only when user scrolls the message up. I can put processor to sleep using ioctl/system call without informing Qt framework.

    In android, we have wakelocks as part of framework, which prevents processor going to sleep when framework is busy doing tasks.
    In Qt where do I put locks ? May be I am lacking know how on how it works.

    Is there any power management framework available in Qt ?

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