Struct Timer 

pub struct Timer { /* private fields */ }

A 64-bit timer based on SysTick.

Stores wraparounds in 2 32-bit atomics. Scales the systick counts to arbitrary frequency.

Implementations

impl Timer

pub fn systick_handler(&self)

SysTick handler.

Call this from the SysTick interrupt handler.

pub fn now(&self) -> u64

Robust now() (VAL-jump tie-breaker, no COUNTFLAG dependency).

Design: One-Wrap Compensation via PendST Detection

This implementation is designed to handle exactly one missed SysTick wrap.

How it works:

1. Uses PendST bit to detect when the SysTick ISR is pending (hardware wrapped but ISR hasn’t run)
2. If PendST is set, adds +1 to the wrap count to compensate for the missed wrap
3. This allows monotonic time even when the ISR is delayed by up to one full wrap period

Design limit: If the SysTick ISR is starved for MORE than one complete wrap period, this compensation becomes insufficient and monotonic violations occur. The ISR starvation detection logic in diagnose_timing_violation() identifies these as catastrophic “N+1 missed wraps”.

pub fn get_syst(&self) -> u32

Returns the current SysTick counter value.

pub const fn reload_value(&self) -> u32

Returns the SysTick reload value configured for this timer.

pub const fn tick_hz(&self) -> u64

Returns the output tick frequency in Hz.

pub const fn new(tick_hz: u64, reload_value: u32, systick_freq: u64) -> Self

Creates a new timer that converts SysTick cycles to ticks at a specified frequency.

Arguments

• tick_hz - The desired output frequency in Hz (e.g., 1000 for millisecond ticks)
• reload_value - The SysTick reload value. Must be between 1 and 2^24-1. This determines how many cycles occur between interrupts.
• systick_freq - The frequency of the SysTick counter in Hz (typically CPU frequency)

Panics

• If reload_value is 0 or greater than 2^24-1 (16,777,215)
• If systick_freq is 0

Examples

// Create a millisecond-resolution timer on a 48MHz CPU with reload value of 47,999
let timer = Timer::new(1000, 47_999, 48_000_000);

pub fn start(&self, syst: &mut SYST)

Call this if you haven’t already started the timer.