Initial public release of WII5 Buoy firmware

Firmware for an autonomous wave-measurement buoy (ATmega2560-based
WII5 v2 board). Reads wave motion from a Sparton AHRS-M1/M2 IMU,
samples GPS and battery state, and reports back over Iridium SBD
satellite telemetry. Originally developed 2012-2024.

This is the first public release. Code, documentation, and field-tested
operating modes (Capture, Sleep, Position, ManualTest, SelfTest,
LowBattery) are licensed under Apache 2.0 — see LICENSE and NOTICE.

See README.md for an overview and build instructions, CONTRIBUTING.md
for how to contribute, and DEPLOYMENTS.md for the field-deployment log.

WII5Mode.h

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright (c) 2012-2024 Scott Penrose <scottp@dd.com.au> and WII5 Buoy contributors
+//
+// This file is part of WII5 Buoy firmware.
+// See LICENSE for full terms.
+
+/**
+ * @file WII5Mode.h
+ * @brief Base class for run-time operating modes (Capture, Sleep, Position, etc.).
+ */
+
+// NOTE: This is a base class for all modes and not really used
+
+#ifndef WII5Mode_h
+#define WII5Mode_h
+
+#include <Arduino.h>
+#include <TimeLib.h>
+#include <WII5.h>
+#include <elapsedMillis.h>
+
+/**
+ * @brief Base class for run-time operating modes.
+ *
+ * Each subclass owns a small state machine that is ticked by
+ * WII5Controller::loop() while that mode is active. Concrete modes
+ * include WII5ModeCapture, WII5ModeSleep, WII5ModePosition,
+ * WII5ModeManualTest, WII5ModeSelfTest, and WII5ModeLowBattery.
+ */
+class WII5Mode {
+  public:
+    /** @brief One-time bring-up. */
+    virtual void begin();
+    /** @brief State-machine tick while this mode is active. */
+    virtual void loop();
+
+  protected:
+    elapsedMillis wait;
+};
+
+#endif