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.

WII5ModeLowBattery.h

@@ -0,0 +1,67 @@
+// 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 WII5ModeLowBattery.h
+ * @brief Declares WII5ModePosition (position mode).
+ *
+ * @note The WII5ModePosition.h / WII5ModeLowBattery.h header pair are
+ * swapped relative to their filenames in this codebase: this file
+ * (WII5ModeLowBattery.h) declares class WII5ModePosition, and
+ * WII5ModePosition.h declares class WII5ModeLowBattery. The corresponding
+ * .cpp files match their filenames. TODO: untangle and rename.
+ */
+
+#ifndef WII5ModePosition_h
+#define WII5ModePosition_h
+
+#include <Arduino.h>
+#include <WII5.h>
+#include <TimeLib.h>
+
+enum WII5POSITION_STEPS {
+  WII5POSITION_START,
+  WII5POSITION_STROBE,
+  WII5POSITION_TIME,
+  WII5POSITION_GPS_START,
+  WII5POSITION_GPS_WAIT,
+  WII5POSITION_IRIDIUM_WAIT,
+  WII5POSITION_END
+};
+
+/**
+ * @brief Position mode: periodic GPS + Iridium telemetry only.
+ *
+ * Lower-power than full Capture mode: turns on GPS, gets a fix, sends
+ * a position via Iridium SBD, then idles until the next position window.
+ * No IMU capture, no SD writes.
+ */
+class WII5ModePosition : public WII5Mode {
+  public:
+		WII5ModePosition() {}
+    /** @brief Reset to WII5POSITION_START. */
+    void reset();
+    /** @brief One-time bring-up. */
+    void begin();
+    /** @brief State-machine tick. */
+    void loop();
+    /** @brief Begin a position acquisition cycle. */
+    void start();
+    /** @brief Abort the current cycle. */
+    void stop();
+
+  protected:
+    bool first;
+    elapsedMillis displayWait;
+    elapsedMillis wait;
+    WII5POSITION_STEPS step;
+    WII5POSITION_STEPS lastStep;
+    uint32_t minutes; // since midnight.
+};
+
+extern WII5ModePosition wii5ModePosition;
+
+#endif