Split embassy crate into embassy-executor, embassy-util.

1 files changed, 91 insertions, 0 deletions

diff --git a/embassy-executor/src/time/mod.rs b/embassy-executor/src/time/mod.rs
new file mode 100644
index 000000000..b787a5cf2
--- /dev/null
+++ b/embassy-executor/src/time/mod.rs
@@ -0,0 +1,91 @@
+//! Timekeeping, delays and timeouts.
+//!
+//! Timekeeping is done with elapsed time since system boot. Time is represented in
+//! ticks, where the tick rate is defined by the current driver, usually to match
+//! the tick rate of the hardware.
+//!
+//! Tick counts are 64 bits. At the highest supported tick rate of 1Mhz this supports
+//! representing time spans of up to ~584558 years, which is big enough for all practical
+//! purposes and allows not having to worry about overflows.
+//!
+//! [`Instant`] represents a given instant of time (relative to system boot), and [`Duration`]
+//! represents the duration of a span of time. They implement the math operations you'd expect,
+//! like addition and substraction.
+//!
+//! # Delays and timeouts
+//!
+//! [`Timer`] allows performing async delays. [`Ticker`] allows periodic delays without drifting over time.
+//!
+//! An implementation of the `embedded-hal` delay traits is provided by [`Delay`], for compatibility
+//! with libraries from the ecosystem.
+//!
+//! # Wall-clock time
+//!
+//! The `time` module deals exclusively with a monotonically increasing tick count.
+//! Therefore it has no direct support for wall-clock time ("real life" datetimes
+//! like `2021-08-24 13:33:21`).
+//!
+//! If persistence across reboots is not needed, support can be built on top of
+//! `embassy_executor::time` by storing the offset between "seconds elapsed since boot"
+//! and "seconds since unix epoch".
+//!
+//! # Time driver
+//!
+//! The `time` module is backed by a global "time driver" specified at build time.
+//! Only one driver can be active in a program.
+//!
+//! All methods and structs transparently call into the active driver. This makes it
+//! possible for libraries to use `embassy_executor::time` in a driver-agnostic way without
+//! requiring generic parameters.
+//!
+//! For more details, check the [`driver`] module.
+
+#![deny(missing_docs)]
+
+mod delay;
+pub mod driver;
+mod duration;
+mod instant;
+mod timer;
+
+#[cfg(feature = "std")]
+mod driver_std;
+
+#[cfg(feature = "wasm")]
+mod driver_wasm;
+
+pub use delay::{block_for, Delay};
+pub use duration::Duration;
+pub use instant::Instant;
+pub use timer::{with_timeout, Ticker, TimeoutError, Timer};
+
+#[cfg(feature = "time-tick-1000hz")]
+const TPS: u64 = 1_000;
+
+#[cfg(feature = "time-tick-32768hz")]
+const TPS: u64 = 32_768;
+
+#[cfg(feature = "time-tick-1mhz")]
+const TPS: u64 = 1_000_000;
+
+#[cfg(feature = "time-tick-16mhz")]
+const TPS: u64 = 16_000_000;
+
+/// Ticks per second of the global timebase.
+///
+/// This value is specified by the `time-tick-*` Cargo features, which
+/// should be set by the time driver. Some drivers support a fixed tick rate, others
+/// allow you to choose a tick rate with Cargo features of their own. You should not
+/// set the `time-tick-*` features for embassy yourself as an end user.
+pub const TICKS_PER_SECOND: u64 = TPS;
+
+const fn gcd(a: u64, b: u64) -> u64 {
+    if b == 0 {
+        a
+    } else {
+        gcd(b, a % b)
+    }
+}
+
+pub(crate) const GCD_1K: u64 = gcd(TICKS_PER_SECOND, 1_000);
+pub(crate) const GCD_1M: u64 = gcd(TICKS_PER_SECOND, 1_000_000);