... > >> + > >> +COUNT > >> +----- > >> +A Count represents the count data for a set of Signals. The Generic > >> +Counter interface provides the following available count data types: > >> + > >> +* COUNT_POSITION_UNSIGNED: > >> + Unsigned integer value representing position. > >> + > >> +* COUNT_POSITION_SIGNED: > >> + Signed integer value representing position. > > > >Just a thought: As the '0' position is effectively arbitrary is there any > >actual difference between signed and unsigned? If we defined all counters > >to be unsigned and just offset any signed ones so the range still fitted > >would we end up with a simpler interface - there would be no real loss > >of meaning that I can see.. I suppose it might not be what people expect > >though when they see their counters start at a large positive value... > > This is something I've been on the fence about for a while. I would > actually prefer the interface to have simply a COUNT_POSITION data type > to represent position and leave it as unsigned; distinguishing between > signed and unsigned position seems ultimately arbitrary given that it's > mathematically just an offset as you have pointed out. > > If we were to go down this route, then we'd have a count value that may > always be represented using an unsigned data type, with an offset value > that may always be represented using a signed data type -- the > relationship being such: position = count + offset. Is that correct? Given the positions are all arbitrary (such as limits etc) there is no real need to have 0 as in anyway special. So you could just apply an offset to everything then don't make them visible to userspace at all. > > My reason for giving the option for either signed or unsigned position > was to help minimize the work userspace would have to do in order to get > the value in which they're actually interested. I suppose it was a > question of how abstract I want to make the interface -- although, > making it simpler for userspace put more of a burden on the kernel side. > > However, the "offset" value route may actually be more robust in the end > because userspace would have to know whether they want a signed or > unsigned position regardless in order to parse, so with count and offet > defined we know they will always be unsigned and signed respectively. Hmm. It's not obvious to me which is the best option. > > > > > > > > > > >> + > >> +A Count has a count function mode which represents the update behavior > >> +for the count data. The Generic Counter interface provides the following > >> +available count function modes: > >> + > >> +* Increase: > >> + Accumulated count is incremented. > >> + > >> +* Decrease: > >> + Accumulated count is decremented. > >> + > >> +* Pulse-Direction: > >> + Rising edges on quadrature pair signal A updates the respective count. > >> + The input level of quadrature pair signal B determines direction. > >> + > >Perhaps group the quadrature modes for the point of view of this document? > >Might be slightly easier to read? > > > >* Quadrature Modes > > > > - x1 A: etc. > > > >> +* Quadrature x1 A: > >> + If direction is forward, rising edges on quadrature pair signal A > >> + updates the respective count; if the direction is backward, falling > >> + edges on quadrature pair signal A updates the respective count. > >> + Quadrature encoding determines the direction. > >> + > >> +* Quadrature x1 B: > >> + If direction is forward, rising edges on quadrature pair signal B > >> + updates the respective count; if the direction is backward, falling > >> + edges on quadrature pair signal B updates the respective count. > >> + Quadrature encoding determines the direction. > >> + > >> +* Quadrature x2 A: > >> + Any state transition on quadrature pair signal A updates the > >> + respective count. Quadrature encoding determines the direction. > >> + > >> +* Quadrature x2 B: > >> + Any state transition on quadrature pair signal B updates the > >> + respective count. Quadrature encoding determines the direction. > >> + > >> +* 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. > > > > > >__|---|____|-----|____ > >____|----|____|-----|____ > > > >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. Looks rather like the sort of thing that is a side effect of the implementation rather than deliberate. > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
