Until now I did it the simple way, using a flip-flop (in hardware). This has the drawback that the flip-flop always remains in the last state, which always requires to do an additional click, which is interpreted the wrong way around and only then the clicks come in in the correct order.
So I am now eliminating that part. The hardware debouncer remains though, it's great, I can recommend it!
So what I now need to do is to interprete the clicks of 'A' and 'B' into clicks 'clock' and 'counterclock', in software. I think there are two approaches here:
- have a flag on both gpio's that are related (connected to either 'A' or 'B');
* if neither flag is set, set flag on the GPIO that was hit
* if both flags are set, see which one is to be set now (the flag belonging to the GPIO that now hit), if it's the first of the pair, note 'clock', otherwise note 'counterlock'; after that, clear both flags
- set a timestamp on every GPIO when it's hit, check the other GPIO of a pair and see if it's within the time window that a clock on the encoder may take; whichever of the two was the first, determines the direction.
The first solution has the drawback that one really would need to clear all flags after some timeout, because rotary encoders tend to miss contacts and otherwise we'd remain in some stuck state, giving spurious results. The problem is that we don't know when we set the flag, so it may be cleared the nanosecond after it was set. This could be resolved, I guess, by making the cleanup function timed.
The second solution has the drawback of quick timer overflow. We'd really need to have at least microsecond resolution, ideally nanosecond. The timestamp as a 32 bit value would turnover very quickly, giving cause to race conditions. And no, I don't want to have 64 bit timestamp values
I am now using code that does the first, but it doesn't work very well. Probably because the encoders are very cheap and very frequently missing a hit. I guess I need to pull them quite a bit stronger and maybe then it starts working.
So, just brainstorming here.