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Asked: 2026-05-16T06:47:10+00:00

I need to implement the following feature for my device running embedde linux on

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I need to implement the following feature for my device running embedde linux on a 200mhz MIPS cpu:
1) if a reset button is pressed and held for less then a second – proceed with reboot
2) if a reset button is pressed and held for at least 3 sec. – restore the system’s configuration with default values from NVRAM and then reboot.

I’m thinking of two ways:
1) a daemon that constantly polls the button’s state with proper timings via GPIO ioctls
(likely too big overhead, lots of context switching ?)
2) simple char driver polling the button, measuring timings and reporting the state, for example, via /proc to user space where daemon or a shell script can check and do what’s required.

And for both cases I have no idea how to measure the time 🙁
What would you suggest/recommend?

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1 Answer

  1. Editorial Team

    If you want to do this in software, you need to put this in kernel (interrupt) code, rather than in a shell script or daemon. The better approach would be to put this in hardware.

    In my experience, the likely reason for resetting the device will be bad user code which has locked or bricked the processor. If the issue is a corruption of memory due to RF energy or something of that nature, you may require hardware or an external (hardened) processor to reflash the device and fix the problem.

    In the bad-user-code case, processor interrupts and kernel code should continue to run, while user code may be completely stalled. If you can poll the pin from an interrupt, you stand a much better chance of actually getting the reset you expect. Also, this enables you to do event-driven programming, rather than constantly polling the pin.

    One other approach (not to the specs you listed, but a popular method for achieving the same goal) would be to have the startup routines check a GPIO line, and hold a button down when you want to re-initialize the device. On most embedded Linux devices which I’ve seen, the “Reset” button is wired to a dedicated reset pin on the microcontroller, and not to a GPIO pin. You may have to go with this route, unless you want to start cutting traces.

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