libs/kaptan-sensor: add immutable IMU snapshot

libs/kaptan-sensor/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "kaptan-sensor"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+rust-version.workspace = true
+version.workspace = true
+
+[lints]
+workspace = true
+
+[dependencies]
+kaptan-time = { path = "../kaptan-time" }

libs/kaptan-sensor/src/lib.rs

@@ -0,0 +1,43 @@
+//! Hardware-independent sensor observations and units.
+//!
+//! Sensor data is immutable after publication. Bus transactions, queueing,
+//! protocol encoding, PAC access, RTIC mechanics, and board transforms do not
+//! belong in this crate.
+
+#![no_std]
+
+use kaptan_time::Timestamp;
+
+/// Coherent IMU observation in the board body frame.
+///
+/// Acceleration is milligravity, angular rate is milliradians per second, and
+/// temperature is centidegrees Celsius. The board-frame transform is complete
+/// before this value is published.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct ImuSnapshot {
+    /// Monotonic timestamp captured at acquisition interrupt entry.
+    pub timestamp: Timestamp,
+    /// Body-frame acceleration in milligravity.
+    pub acceleration_milligravity: [i16; 3],
+    /// Body-frame angular rate in milliradians per second.
+    pub angular_rate_milliradians_per_second: [i16; 3],
+    /// Sensor temperature in centidegrees Celsius.
+    pub temperature_centidegrees_celsius: i16,
+}
+
+impl ImuSnapshot {
+    /// Creates one accepted IMU observation.
+    pub const fn new(
+        timestamp: Timestamp,
+        acceleration_milligravity: [i16; 3],
+        angular_rate_milliradians_per_second: [i16; 3],
+        temperature_centidegrees_celsius: i16,
+    ) -> Self {
+        Self {
+            timestamp,
+            acceleration_milligravity,
+            angular_rate_milliradians_per_second,
+            temperature_centidegrees_celsius,
+        }
+    }
+}