# qei.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/embedded-hal-1.0.0-alpha.1/src/qei.rs`.
Keywords: rust, rustlang, rust-lang

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    //! Quadrature encoder interface

    /// Quadrature encoder interface
    ///
    /// # Examples
    ///
    /// You can use this interface to measure the speed of a motor
    ///
    /// ```
    /// extern crate embedded_hal as hal;
    /// #[macro_use(block)]
    /// extern crate nb;
    ///
    /// use hal::prelude::*;
    ///
    /// fn main() {
    ///     let mut qei: Qei1 = {
    ///         // ..
    /// #       Qei1
    ///     };
    ///     let mut timer: Timer6 = {
    ///         // ..
    /// #       Timer6
    ///     };
    ///
    ///
    ///     let before = qei.try_count().unwrap();
    ///     timer.try_start(1.s()).unwrap();
    ///     block!(timer.try_wait());
    ///     let after = qei.try_count().unwrap();
    ///
    ///     let speed = after.wrapping_sub(before);
    ///     println!("Speed: {} pulses per second", speed);
    /// }
    ///
    /// # use core::convert::Infallible;
    /// # struct Seconds(u32);
    /// # trait U32Ext { fn s(self) -> Seconds; }
    /// # impl U32Ext for u32 { fn s(self) -> Seconds { Seconds(self) } }
    /// # struct Qei1;
    /// # impl hal::qei::Qei for Qei1 {
    /// #     type Error = Infallible;
    /// #     type Count = u16;
    /// #     fn try_count(&self) -> Result<u16, Self::Error> { Ok(0) }
    /// #     fn try_direction(&self) -> Result<::hal::qei::Direction, Self::Error> { unimplemented!() }
    /// # }
    /// # struct Timer6;
    /// # impl hal::timer::CountDown for Timer6 {
    /// #     type Error = Infallible;
    /// #     type Time = Seconds;
    /// #     fn try_start<T>(&mut self, _: T) -> Result<(), Infallible> where T: Into<Seconds> { Ok(()) }
    /// #     fn try_wait(&mut self) -> ::nb::Result<(), Infallible> { Ok(()) }
    /// # }
    /// ```
    // unproven reason: needs to be re-evaluated in the new singletons world. At the very least this needs a
    // reference implementation
    pub trait Qei {
        /// Enumeration of `Qei` errors
        type Error;

        /// The type of the value returned by `count`
        type Count;

        /// Returns the current pulse count of the encoder
        fn try_count(&self) -> Result<Self::Count, Self::Error>;

        /// Returns the count direction
        fn try_direction(&self) -> Result<Direction, Self::Error>;
    }

    /// Count direction
    #[derive(Clone, Copy, Debug, Eq, PartialEq)]
    pub enum Direction {
        /// 3, 2, 1
        Downcounting,
        /// 1, 2, 3
        Upcounting,
    }