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PDF export heat up i.mx6



  • Hi,
    i use an i.mx6 cpu with linux os for a qt5.4.1 application.
    In this application i use the following function to export some html pages to pdf files.

    bool PdfExport::exportFile(const char *path) {
        QWebPage page;
        page.mainFrame()->setHtml(exportString().c_str());
    
        // printer is a QPrinter member variable of the PdfExport class
        printer->setPageMargins(5, 5, 5, 5, QPrinter::Millimeter);
        printer->setOutputFileName(path);
        printer->setPageSize(QPrinter::A4);
        printer->setPrintRange(QPrinter::AllPages);
    
        page.mainFrame()->print(printer);
    
        return true;
    }
    

    As long as i do not call the function, my cpu has a constant temperature of 45°C (CPU load ~35%).
    But after i call it the temperature rise quickly to around 60°C, stays there and does not went down any more. Even if i wait an hour or so. CPU usage is furthermore at ~35%.
    I think the GPU will heat up the chip, but why? My function does not hang and returns in a split second.


  • Qt Champions 2018

    Here http://forum.solid-run.com/linux-on-cubox-i-and-hummingboard-f8/temperatures--t490.html
    I found the information that 85-90 degree is normal for that CPU.
    How long do you wait before you execute exportFile()? Maybe 60 degree is normal.



  • I have waited different times. The longest was around 1 and a half our, and the temperature was never higher than 45°C.
    Then i call the export function and the temperature rise up to 60°C in less then 20 seconds and stays there until i close my application. If my application is not running and the os is idle the temperature is around 38°C.

    So 60°C is definitely not normal.



  • Perhaps your printer object has been stuck in a loop of some sort. You could delete the printer after printing and see what happens. Perhaps printer could be a local in that function and be deleted automatically when not needed anymore, but you are best in thinking of such architectural questions.


  • Qt Champions 2018

    @PhTe Can you verify that your application is really not running if you close it? Is the process terminated? Maybe it is still running in the background and consumes CPU.



  • Hey,
    thanks for your help.
    It figured out, that the problem was not the export process. Sorry :)

    It was the message window i show when the export is complete.
    I dont know why but it caused the gpu to heat up even if it was closed.