78 lines
3.5 KiB
Rust
78 lines
3.5 KiB
Rust
///! Digital Input 0 (DI0) reference clock timestamper
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///!
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///! This module provides a means of timestamping the rising edges of an external reference clock on
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///! the DI0 with a timer value from TIM5.
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///!
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///! # Design
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///! An input capture channel is configured on DI0 and fed into TIM5's capture channel 4. TIM5 is
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///! then run in a free-running mode with a configured tick rate (PSC) and maximum count value
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///! (ARR). Whenever an edge on DI0 triggers, the current TIM5 counter value is captured and
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///! recorded as a timestamp. This timestamp can be either directly read from the timer channel or
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///! can be collected asynchronously via DMA collection.
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///!
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///! To prevent silently discarding timestamps, the TIM5 input capture over-capture flag is
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///! continually checked. Any over-capture event (which indicates an overwritten timestamp) then
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///! triggers a panic to indicate the dropped timestamp so that design parameters can be adjusted.
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///!
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///! # Tradeoffs
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///! It appears that DMA transfers can take a significant amount of time to disable (400ns) if they
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///! are being prematurely stopped (such is the case here). As such, for a sample batch size of 1,
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///! this can take up a significant amount of the total available processing time for the samples.
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///! This module checks for any captured timestamps from the timer capture channel manually. In
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///! this mode, the maximum input clock frequency supported is dependant on the sampling rate and
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///! batch size.
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///!
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///! This module only supports DI0 for timestamping due to trigger constraints on the DIx pins. If
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///! timestamping is desired in DI1, a separate timer + capture channel will be necessary.
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use super::{hal, timers};
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/// The timestamper for DI0 reference clock inputs.
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pub struct InputStamper {
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_di0_trigger: hal::gpio::gpioa::PA3<hal::gpio::Alternate<hal::gpio::AF2>>,
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capture_channel: timers::tim5::Channel4InputCapture,
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}
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impl InputStamper {
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/// Construct the DI0 input timestamper.
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///
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/// # Args
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/// * `trigger` - The capture trigger input pin.
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/// * `timer_channel - The timer channel used for capturing timestamps.
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pub fn new(
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trigger: hal::gpio::gpioa::PA3<hal::gpio::Alternate<hal::gpio::AF2>>,
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timer_channel: timers::tim5::Channel4,
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) -> Self {
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// Utilize the TIM5 CH4 as an input capture channel - use TI4 (the DI0 input trigger) as the
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// capture source.
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let mut input_capture =
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timer_channel.into_input_capture(timers::tim5::CaptureSource4::TI4);
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// Do not prescale the input capture signal - require 8 consecutive samples to record an
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// incoming event - this prevents spurious glitches from triggering captures.
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input_capture.configure_filter(timers::InputFilter::Div1N8);
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Self {
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capture_channel: input_capture,
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_di0_trigger: trigger,
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}
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}
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/// Start to capture timestamps on DI0.
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#[allow(dead_code)]
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pub fn start(&mut self) {
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self.capture_channel.enable();
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}
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/// Get the latest timestamp that has occurred.
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///
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/// # Note
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/// This function must be called at least as often as timestamps arrive.
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/// If an over-capture event occurs, this function will clear the overflow,
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/// and return a new timestamp of unknown recency an `Err()`.
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/// Note that this indicates at least one timestamp was inadvertently dropped.
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#[allow(dead_code)]
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pub fn latest_timestamp(&mut self) -> Result<Option<u32>, Option<u32>> {
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self.capture_channel.latest_capture()
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}
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}
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