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by dale_glass
1185 days ago
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I was referring to that yes, even if Linux performs well in the ideal case, it's not necessarily reliable, and the possible problems are hard to compensate for. Eg, your process can randomly get stuck because something in the background is checking for updates and IO is being much slower than usual, or the system ran out of RAM and everything got bogged down by swap. On a microcontroller you just don't have anything else running, so those risks don't exist. Eg, a 3D printer controls a MOSFET to enable/disable the heaters. The system can overheat and actually catch on fire if something makes the software get bogged down badly enough. On a Linux system there's a whole bunch of stuff that can go wrong, most of which is completely outside the software you actually wanted to run. |
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Sure, a single purpose MCU controlling a heater MOSFET has a lot fewer failure modes than a Linux device doing the same.
I don't dispute there are a lot fewer ways it's even possible for that system to misbehave.
The original comment was recommending ESP32s over Raspberry Pis for DIY projects like opening your curtains or flashing LEDs. The ESP IDF runs on FreeRTOS, so we're already moving away from the bulletproof single task MCU. People will almost certainly be adding some custom rolled HTTP webserver on top. They might be leaking memory all over the place, there are probably all kinds of interrupts they have no idea about firing off in the background. I wouldn't trust an ESP32 curtain-bot not to strangle me any more than I'd trust a Raspberry Pi based one.
Your example about running out of RAM seems just as relevant to MCUs. You can leak memory and crash an MCU. You can overload an MCU with tasks and degrade performance. You can use cgroups or ulimit to help prevent a bad process from bringing Linux down.
I agree that Linux is not going to be as reliable as going baremetal, and I'm not recommending you use it as a motor controller. But even the most reliable MCU can fail. An MCU can get hit by cosmic rays or ESD. People might spill water on the 3d printer or physically damage it. It's not even a binary "works right or dies" thing. I've voltage glitched MCUs to get them to skip instructions and get into an unanticipated state.
In any case, the best path to safety is to imagine that the computer might be taken over by Skynet and do everything in its power to kill you. Or worse, ruin your print. If safety is the goal it's probably best to achieve through requiring the computer system to take some positive action to keep the heater on. Or even better, a feedback safety mechanism like a thermal fuse.