refac(hal-x86_64): move pit and tsc into time (#356)

This commit moves the `pit` and `tsc` modules out of `interrupt` and
`cpu`, and into a new `time` module. This feels like a better
organization of things, IMO.

hal-x86_64/src/cpu.rs

@@ -4,9 +4,7 @@ use mycelium_util::bits;
 pub mod entropy;
 pub mod intrinsics;
 mod msr;
-mod tsc;
 pub use self::msr::Msr;
-pub use self::tsc::Rdtsc;
 
 #[repr(transparent)]
 pub struct Port {
@@ -246,7 +244,7 @@ impl FeatureNotSupported {
         self.0
     }
 
-    pub(in crate::cpu) fn new(feature_name: &'static str) -> Self {
+    pub(crate) fn new(feature_name: &'static str) -> Self {
         Self(feature_name)
     }
 }

hal-x86_64/src/cpu/entropy.rs

@@ -4,7 +4,7 @@ use mycelium_util::sync::spin;
 use raw_cpuid::CpuId;
 
 #[cfg(feature = "rand_core")]
-use super::Rdtsc;
+use crate::time::Rdtsc;
 #[cfg(feature = "rand_core")]
 use mycelium_util::sync::Lazy;
 #[cfg(feature = "rand_core")]

hal-x86_64/src/interrupt.rs

@@ -5,11 +5,9 @@ use mycelium_util::{bits, fmt};
 
 pub mod idt;
 pub mod pic;
-pub mod pit;
 
 pub use idt::Idt;
 pub use pic::CascadedPic;
-pub use pit::PIT;
 
 pub type Control = &'static mut Idt;
 
@@ -227,7 +225,7 @@ impl hal_core::interrupt::Control for Idt {
             use core::sync::atomic::Ordering;
             // if we weren't trying to do a PIT sleep, handle the timer tick
             // instead.
-            let was_sleeping = pit::SLEEPING
+            let was_sleeping = crate::time::pit::SLEEPING
                 .compare_exchange(true, false, Ordering::AcqRel, Ordering::Acquire)
                 .is_ok();
             if !was_sleeping {

hal-x86_64/src/lib.rs

@@ -24,6 +24,7 @@ pub mod mm;
 pub mod segment;
 pub mod serial;
 pub mod task;
+pub mod time;
 pub mod vga;
 
 pub const NAME: &str = "x86_64";

hal-x86_64/src/time.rs

@@ -0,0 +1,38 @@
+//! x86 hardware timers and timekeeping functionality.
+pub(crate) mod pit;
+mod tsc;
+pub use self::{
+    pit::{Pit, PIT},
+    tsc::Rdtsc,
+};
+use core::fmt;
+pub use core::time::Duration;
+
+/// Error indicating that a [`Duration`] was invalid for a particular use.
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub struct InvalidDuration {
+    duration: Duration,
+    message: &'static str,
+}
+
+// === impl InvalidDuration ===
+
+impl fmt::Display for InvalidDuration {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { duration, message } = self;
+        write!(f, "invalid duration {duration:?}: {message}")
+    }
+}
+
+impl InvalidDuration {
+    /// Returns the [`Duration`] that was invalid.
+    #[must_use]
+    pub fn duration(self) -> Duration {
+        self.duration
+    }
+
+    #[must_use]
+    pub(crate) fn new(duration: Duration, message: &'static str) -> Self {
+        Self { duration, message }
+    }
+}