bk99.de entertain the web since 1997

bk99.de
Hackaday · Real timeCurated

Using Linux for time-critical tasks

Summary

Using a Raspberry Pi and a stepper motor, Hackaday explains why normal Linux fluctuates and which measures improve soft real-time behaviour. The experiment uses a 28BYJ-48 stepper motor. A ULN2003 drives its windings.

Ideas

  • A stepper motor makes timing deviations immediately visible.
  • Memory pressure can swap out a control process for seconds.
  • mlockall keeps the required memory pages in RAM.
  • An oscilloscope shows jitter more precisely than visible movement.

Insights

  • A fast response on average does not guarantee a maximum response time.
  • Measurable worst-case latency decides whether a controller is suitable.
  • Hard real time often belongs on a separate microcontroller.

Facts

  • Normal Linux is not a hard real-time operating system.

Recommendations

  • Measure latency under CPU, memory and I/O load.
  • Move safety-critical timing control to suitable hardware.

References

Read the original article

Search the Web Archive

Hackaday · 2012

Linux controls a real 6502 processor

Hackaday shows how a BeagleBone loads, starts and operates a discrete 6502 as a remote processor from Linux via GPIO. The project uses a discrete 6502. An ARM-based BeagleBone serves as the host.

Hackaday · 2026

Several Linux kernels run without a hypervisor

Hackaday presents Multikernel Linux, in which a host kernel divides up the hardware and starts further independent Linux kernels directly on bare metal. The project is called Multikernel Linux. It is not the historical microkernel-based MkLinux.

Hackaday · 2026

Why Linux applications are hard to distribute

Hackaday describes the multitude of distribution packages, language managers, third-party sources, AppImage and Flatpak as a burden for application authors. The Fresh editor serves as a concrete example. APT, AUR, Homebrew, AppImage and Flatpak are named.