On Saturday 05 December 2015 20:50:18 Daniel Mack wrote: > On 12/03/2015 02:01 PM, Rojhalat Ibrahim wrote: > > On Wednesday 02 December 2015 19:59:20 Uwe Kleine-König wrote: > > >> I have a real rotary encoder with 4 input lines and so 16 > >> distinguishable positions. It would be described as: > >> > >> compatible = "rotary-encoder"; > >> gpios = <&gpio4 12 GPIO_ACTIVE_HIGH>, <&gpio4 11 GPIO_ACTIVE_HIGH>, <&gpio4 10 GPIO_ACTIVE_HIGH>, <&gpio4 9 GPIO_ACTIVE_HIGH>; > >> rotary-encoder,steps = <16>; > >> rotary-encoder,steps-per-period = <16>; > >> > >> with the binding implemented in my patches. > >> > >> The wikipedia article about rotary encoders[1] uses a device with 3 > >> input lines to explain gray encoding. So I didn't consider "my" device > >> as exotic up to now. > >> > > > > So you have an absolute encoder. From the state of the four input lines you > > can determine the absolute position value. There is no need to count steps. > > At least that's the original purpose of your device. > > > > Of course it might be conceivable to use that kind of absolute encoder in an > > incremental way and count the steps throughout multiple revolutions. > > But why would you do that? The resolution of 16 steps per revolution is not > > very good (incremental encoders often have hundreds or thousands of steps per > > revolution). And the whole point of an absolute encoder is that you are able > > to determine the current position at any time just by looking at the inputs > > without having to count steps. > > Yes, you're right, that's actually a very different kind of device which > should be supported with a different mode or something, so that the > output of the driver reflects the absolute state of the encoder. This > even simplifies things in the driver: The entire state logic would be > bypassed in this mode, and the current state of the GPIO lines would be > used directly to get the absolute value. Makes sense? > Definitely makes sense to me. Thanks. Rojhalat > > Thanks, > Daniel > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
