Auto-save M122 on power-down

[wilriker]

Background

The idea for this sparked in this thread.

The Duet is capable of detection a power-down. Often times here it is requested to provide the output of M122 after an unexpected reboot so the error can be better analyzed. More often than not users have already power-cycled their Duet and so this information is lost.

Request

To save this information across a restart it could be possible to have RRF write the result of M122 together with a timestamp (whatever is available here) on power-down/power-loss to e.g. /sys/diagnostics unless it was printing at this time since everything configured with M911 clearly has to take precedence then.

[dc42]

There might be enough time to do that. It wouldn't help if the user had restarted using Emergency Stop or M999 or the reset button.

[wilriker]

@dc42 Yes, there still are cases, where this won't work, but at least it will cover some more bases than now.