[PATCH v6 3/9] docs: Add Generic Counter interface documentation

On 05/22/2018 07:08 PM, Jonathan Cameron wrote:

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+* Quadrature x2 Rising:
+  Rising edges on either quadrature pair signals updates the respective
+  count. Quadrature encoding determines the direction.  

This one I've never met.  Really? There are devices who do this form
of crazy? It gives really uneven counting and I'm failing to see when
it would ever make sense...  References for these odd corner cases
would be good.


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001122222223334444444  

That's the same reaction I had when I discovered this -- in fact the
STM32 LP Timer is the first time I've come across such a quadrature
mode. I'm not sure of the use case for this mode, because positioning
wouldn't be precise as you've pointed out. Perhaps Fabrice or Benjamin
can probe the ST guys responsible for this design choice to figure out
the rationale.

Hmm.  My inclination would be to not support it unless someone can up
with a meaningful use.  We are adding ABI (be it not much) for a case
that to us makes no sense.

Hi Jonathan, William,

Sorry for the late reply. To follow your advise, we can probably drop
this for now. I think simple counter, or quadrature x4 will be mostly
used for now. As you pointed out, there's not much ABI for x2
rising/falling cases. It will not be a big deal to add it later if needed.

I can help to update (remove & test) this in LP-Timer counter driver if
you wish.

Please let me know,

Thanks,
Fabrice

Looks rather like the sort of thing that is a side effect of the
implementation rather than deliberate.

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I'm leaving in these modes for now, as they do exist in the STM32 LP
Timer, but it does make me curious what the intentions for them were
(perhaps use cases outside of traditional quadrature encoder
positioning).

Sure if there is a usecase then fair enough.

Jonathan