stabilizer 0.11.0

//! Digital Input 0 (DI0) reference clock timestamper
//!
//! This module provides a means of timestamping the rising edges of an external reference clock on
//! the DI0 with a timer value from TIM5.
//!
//! # Design
//! An input capture channel is configured on DI0 and fed into TIM5's capture channel 4. TIM5 is
//! then run in a free-running mode with a configured tick rate (PSC) and maximum count value
//! (ARR). Whenever an edge on DI0 triggers, the current TIM5 counter value is captured and
//! recorded as a timestamp. This timestamp can be either directly read from the timer channel or
//! can be collected asynchronously via DMA collection.
//!
//! To prevent silently discarding timestamps, the TIM5 input capture over-capture flag is
//! continually checked. Any over-capture event (which indicates an overwritten timestamp) then
//! triggers a panic to indicate the dropped timestamp so that design parameters can be adjusted.
//!
//! # Tradeoffs
//! It appears that DMA transfers can take a significant amount of time to disable (400ns) if they
//! are being prematurely stopped (such is the case here). As such, for a sample batch size of 1,
//! this can take up a significant amount of the total available processing time for the samples.
//! This module checks for any captured timestamps from the timer capture channel manually. In
//! this mode, the maximum input clock frequency supported is dependant on the sampling rate and
//! batch size.
//!
//! This module only supports DI0 for timestamping due to trigger constraints on the DIx pins. If
//! timestamping is desired in DI1, a separate timer + capture channel will be necessary.
use super::{hal, timers};

/// The timestamper for DI0 reference clock inputs.
pub struct InputStamper {
    _di0_trigger: hal::gpio::gpioa::PA3<hal::gpio::Alternate<2>>,
    capture_channel: timers::tim5::Channel4InputCapture,
}

impl InputStamper {
    /// Construct the DI0 input timestamper.
    ///
    /// # Args
    /// * `trigger` - The capture trigger input pin.
    /// * `timer_channel - The timer channel used for capturing timestamps.
    pub fn new(
        trigger: hal::gpio::gpioa::PA3<hal::gpio::Alternate<2>>,
        timer_channel: timers::tim5::Channel4,
    ) -> Self {
        // Utilize the TIM5 CH4 as an input capture channel - use TI4 (the DI0 input trigger) as the
        // capture source.
        let mut input_capture =
            timer_channel.into_input_capture(timers::tim5::CaptureSource4::Ti4);

        // Do not prescale the input capture signal - require 8 consecutive samples to record an
        // incoming event - this prevents spurious glitches from triggering captures.
        input_capture.configure_filter(timers::InputFilter::Div1N8);

        Self {
            capture_channel: input_capture,
            _di0_trigger: trigger,
        }
    }

    /// Start to capture timestamps on DI0.
    #[allow(dead_code)]
    pub fn start(&mut self) {
        self.capture_channel.enable();
    }

    /// Get the latest timestamp that has occurred.
    ///
    /// # Note
    /// This function must be called at least as often as timestamps arrive.
    /// If an over-capture event occurs, this function will clear the overflow,
    /// and return a new timestamp of unknown recency an `Err()`.
    /// Note that this indicates at least one timestamp was inadvertently dropped.
    #[allow(dead_code)]
    pub fn latest_timestamp(&mut self) -> Result<Option<u32>, Option<u32>> {
        self.capture_channel.latest_capture()
    }
}