Messages in this thread | | | Subject | Re: [PATCH] iio: add channel type for frequency | From | David Lechner <> | Date | Mon, 2 Jul 2018 10:33:52 -0500 |
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On 07/02/2018 08:03 AM, Jonathan Cameron wrote: > On Sun, 1 Jul 2018 17:24:34 -0500 > David Lechner <david@lechnology.com> wrote: > >> On 07/01/2018 02:18 AM, Lars-Peter Clausen wrote: >>> On 07/01/2018 04:59 AM, David Lechner wrote: >>>> This adds a new type for frequency to the IIO channel type enumeration. >>>> >>>> Units are in Hz. >>>> >>> >>> Documentation? >> >> I take it that you mean Documentation/ABI/testing/sysfs-bus-iio? Or >> somewhere else too? > > Yes. > >> >>> >>> We already have the altvoltage channel type with the frequency attribute. >>> Difficult to say if there are any overlaps without documentation on how this >>> new attribute is supposed to be used. >> >> I'm basically trying to implement a quadrature encoder in iio. I want to be >> able to use it in-kernel to get a rotational speed value for a motor. > > Have you seen the counters subsystem work that is pretty much ready to merge?
I hadn't seen that. Thanks. It sounds like the way to go since I am dealing with a quadrature encoder.
> > https://lkml.org/lkml/2018/6/21/659 > >> >> The motors (and encoder wheels) are hot-swapable, so we don't know how many >> counts from the quadrature encoder equals one rotation because it depends on >> which motor is being used. So using IIO_ANGL_VEL doesn't work for this case. > > Hmm. This always ugly when we have hotswappable external devices. Ideal is > to describe them with device tree or similar none the less as this stuff isn't > really something userspace should have to figure out. > >> >> It seems to me that the proper generic unit for "speed" from the quadrature >> encoder would be counts per second, hence the suggestion of a frequency unit. > > It is probably not that clear cut, as what is it frequency of? All depends on > what mode the quadrature counter is working in x4 or x1 for simplest options. > > >> I'm not sure if voltage frequency works here since a "count" on a quadrature >> encoder is derived from two different voltage signals (and may vary depending >> on how the encoder determines what one count it). >> >> Also, unrelated to my quadrature encoder project, I was thinking that >> frequency counters would use this unit as well (although the voltage alt >> makes more sense for this case). >> >> There are also sound sensors that measure frequency that could use this unit. > > I have not fundamental issue with having a frequency channel, but only > if we have a clear cut use case. I suspect the right option here is to > look at what extensions are needed to William's counter subsystem instead > of in IIO (which frankly failed to stretch far enough to support counters > well). >
Agreed. Let's drop this patch.
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