UM2 Warm Up Sequence

[Daid 306]

I think Daid's point is that if you add a 10 second timer and you have a tiny bug in the code you might defeat the existing safety features. What if there is a subtle bug that occasionally resets the 10 second timer - often enough to cause it to melt. What if the timer gets set to negative -4000 seconds so that it doesn't time out for an hour. These kinds of bugs aren't normally tested for because to test for it you have to purposely disconnect the thermocouple wire. That is the potential danger here.

Anyway I still disagree with Daid - if the code was not in the normal set of operations but if instead you had a special menu item that blocked all interrupts (or stopped returning from the loop or however it works) for 10 seconds (ignored USB also) and just turned on the heaters for those 10 seconds. Then you wouldn't have to worry about introducing a new bug that circumvents safety. The code would be self contained and not normally used (not used from any gcode for example).

 

You're free to disagree with me. But I think I have a tiny bit more experience with safety systems. After all, I spend a few years working on safety systems for traffic lights. I could tell you about a lovely bug that shut down a whole island of traffic lights... it was a timer, that disabled a safety check for a few seconds.

You keep safety systems as small and controllable as possible, any added complexity adds chance for bugs. With all the people hacking in the firmware already, it's already difficult to get a full grasp on the quality.

Disabling all interrupts for 10 seconds would cause a hardware watchdog timeout. Which resets and hangs the system (disabling all outputs) this hardware watchdog is in place to make sure the firmware keeps checking the temperature properly. So you would have to disable the final failsafe system. Kinda what they did in Chernobyl.