On Thu, 12 Nov 2020 12:20:48 +0100, Oleksij Rempel wrote: > According to the TI application bulletin [1] we deal with two generic > mechanisms which would affect the precision of provided input events: > > |TOUCH SCREEN SETTLING TIME > | > |When the touch panel is pressed or touched, there are > |two mechanisms that will affect the voltage level at the contact point of > |the touch panel. These two mechanisms will cause the voltage across the > |touch panel to “ring” (oscillate), and then slowly settle (decay) > |down to a stable DC value. > | > |The two mechanisms are: > | 1) Mechanical bouncing caused by vibration of the top layer sheet of > | the touch panel when the panel is pressed. > | > | 2) Electrical ringing due to parasitic capacitance between the top > | and bottom layer sheets of the touch panel and at the input of ADS7843 > | that causes the voltage to “ring”(oscillate). > > Since both of this mechanisms are board specific and reflect the > mechanical, and electrical properties of end product, it is better to > provide a generic properties to address them. > > The touchscreen-read-duration-us property should address 1. mechanism. > This effect can be triggered by device specific design. The duration ma be > dependent on the use case of the end device. For example a touch where > writing is required may have other timing requirements as the device > where only "buttons" should be pressed. > > The touchscreen-settling-time-us property should address 2. mechanism > where the size and construction of touch screen plates affect the parasitic > capacitance and time needed between enabling power supply for the > plates, and actual usable voltage level to detect the position of touch event. > > [1] https://www.ti.com/lit/an/sbaa036/sbaa036.pdf > > Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> > --- > .../bindings/input/touchscreen/touchscreen.yaml | 9 +++++++++ > 1 file changed, 9 insertions(+) > Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
