[Ovmsdev] Event task

Mark Webb-Johnson mark at webb-johnson.net
Sat Apr 7 17:26:05 HKT 2018

I’m seeing a timing/stack/mutex/whatever issue with the new 3.1 modules, regarding sd card auto-mounting at boot.

Currently we are using a freertos timer to auto-mount this 500ms after insertion. That fires off some events (sd.inserted, sd.mounted) and I have a script on sd.mounted that does some things like turn on log file to /sd/ovms.log. That is failing (locking up SD). In general, as Michael pointed out, doing big things in freertos timers is not recommended.

I tried a quick fix to change to use ticker.1 and housekeeping timers. But, then in ticker.1 we SignalEvent sd.inserted and sd.mounted, and that leads to a whole new set of problems (raising a signal inside a signal handler).

Overall, it seems messy. The housekeeping task (where we like to run these things) is also very basic at the moment.

I think the better solution maybe to remove the housekeeping task completely, and replace it with an event task reading events off a queue and firing them to all listeners. Then change SignalEvent to queue an event to the event task so that the event task fires the actual event in it’s own time and in it’s own large stack.

The slight change here is that we would still guarantee in-order delivery of events raised, but the caller of SignalEvent would immediately get back control (even if the signal had not been dispatched to all listeners yet).

OK? Any better suggestions?

Regards, Mark

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