"It may be important that the `..." <- I changed the code to use `modify`, and whatever else I was trashing, it's still incrementing at 1Mhz... Take 2: ```rust #[pre_init] unsafe fn pre_init() { // SAFETY: `#[pre_init] fn` runs before stage 1 bootloader, still in privileged thread mode. // Any access of memory, including any static variables, will result in undefined behavior. // (see https://docs.rs/cortex-m-rt/latest/cortex_m_rt/attr.pre_init.html for more details) let timer_0 = rp_pac::TIMER0; // Switch `SOURCE` to `CLK_SYS` (instead of 1 µs tick) timer_0.source().modify(|source| source.clk_sys()); // Lock configuration--`TIMER0` now read-only (until reset) timer_0.locked().modify(|lock| lock.set_locked(true)); } ``` Anyone have any thoughts?