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There is a small patch to allwow the kernel to make a sysfs entry that Linuxcnc and some other programs use to determine if the kernel is a realtime kernel.

forum.linuxcnc.org/media/kunena/attachme...ernel-realtime.patch

forum.linuxcnc.org/38-general-linuxcnc-q...6-12?start=10#315437

@ elovalvo Thanks for your work on this. I am trying to stay within RPI OS and compiling my own kernel. Can you tell me why I still have to patch the kernel, even though RT_PREEMPT is supposed to be a part of the mainstream kernel now? I am using the latest 6.6.74.

>Len

Desiccant sounds good at first, but these do "fill up" quickly. I have dozens of these bags in a 3D printer filament storage container. Even though it is completely sealed (with a gasket), all those bags are only good for about a year. Then they all must be baked at 110degC for 8-12h to rejuvenate them; moisture is insidious.

If you try this, place a quality hygrometer inside. Will likely find that the humidity stays low for only a month or so, even with a good seal.

The moisture alone probably is not causing the inability to start. The way most computers and power supplies are designed, just is not favorable to low temperatures. Very few are, because that is not a typical use case for a computer. Section 5.6 of the RaspberryPi4B says that is good down to 0degC - but then must consider whatever power supply is used for it. The characteristics of semiconducting materials changes as temperature changes, so functionality at low temps has to be something designed into it. Once had a quirky home computer that "complained" at 19degC and refused to run at 18.

If it were my machine, I'd put a heater (like a hair dryer on low setting) near the computer, along with a thermostat. Set the thermostat to say 20degC, and just let it warm up until the thermostat starts cycling. Of course need to be careful nothing can get too hot. Warming should take an hour or more - rushing it is not advised; the whole computer needs to warm up slowly. Then run the machine. That may be easier than re-engineering a quirky power supply or replacing the computer.  Unless anyone knows of an industrial-rated computer (and power supply.)