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What can cause jitter of real-time tasks?

As long as no other real-time software or similar system-critical software is installed, (almost) nothing exists, which interrupts or delays the real-time task except:

  • CLI = general interrupt blocked through Windows and drivers.
    Unfortunately, no software can do something against it. However, in Windows the blocking time is limited and almost certainly a driver is responsible for this. In this case the respective driver has to be replaced. Because it is difficult to determine it we offer payed help on such cases by our support team.
  • WBINVD = command to flush the entire internal cache.
    According to experience, only Nvidia graphic drivers cause such and should be replaced with an ATI (AMD) graphics card.
  • C1E = Enhanced Power Save Mode of the CPU.
    Especially, the overdeveloped Intel CPUSs (i7, Xeon, …) switch to idle mode after short breaks, delaying the wake up after a timer interrupt up to several milliseconds.
    This can be switched off in the BIOS (see CIE or similar) or the PC is not real-time capable.
  • Ordinary Windows activities cannot replace real-time tasks.
    Windows has the priority 0, whereas the RealTime tasks have priorities from 1 to 255. DPC has no influence.
  • To achieve the best real-time behavior use the dedicated mode, which supports the exclusive use of single CPU cores in real-time. Without Windows influence the maximum jitter will be less than 1 us.