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//! Support for RISC-V's timers, using the Sstc extension.
#![cfg(target_arch = "riscv64")]
#![no_std]
use core::{arch::asm, ops::Add, time::Duration};
/// The number of `Instant` "ticks" in a second. Initialized by the early-boot DeviceTree parser.
pub static mut TIMEBASE_FREQUENCY: u32 = 0;
/// A moment in time.
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub struct Instant(u64);
impl Instant {
/// Returns the current time as an `Instant`.
pub fn now() -> Instant {
let out;
// SAFETY: We require the Sstc extension, enable it before jumping to Rust, and never
// disable it.
unsafe {
asm!("rdtime {out}", out = out(reg) out, options(nomem, nostack));
}
Instant(out)
}
}
impl Add<Duration> for Instant {
type Output = Instant;
#[allow(clippy::suspicious_arithmetic_impl)]
fn add(self, duration: Duration) -> Instant {
// SAFETY: TIMEBASE_FREQUENCY is never concurrently written to.
let ticks_per_second = unsafe { TIMEBASE_FREQUENCY };
let ticks = duration.as_nanos().wrapping_mul(ticks_per_second as u128) / 1_000_000_000;
Instant(self.0.wrapping_add(ticks as u64))
}
}
/// Sets the timer interrupt to fire at the given instant. Note that this sets a global value,
/// rather than interacting with the scheduler in any way.
pub fn set_timer(instant: Instant) {
// SAFETY: We require the Sstc extension, enable it before jumping to Rust, and never
// disable it.
unsafe {
asm!("csrw stimecmp, {instant}", instant = in(reg) instant.0, options(nomem, nostack));
}
}
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