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.

WII5ModeSleep.h

@@ -0,0 +1,60 @@
+// 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 WII5ModeSleep.h
+ * @brief Sleep mode: long sleeps between wake-ups; powers down the Maths CPU.
+ */
+
+#ifndef WII5ModeSleep_h
+#define WII5ModeSleep_h
+
+#include <Arduino.h>
+#include <WII5.h>
+#include <TimeLib.h>
+
+// TODO - Namespace these - e.g enum class ...
+enum WII5SLEEP_STEPS {
+   WII5SLEEP_START,
+   WII5SLEEP_WAIT,
+   WII5SLEEP_SLEEPING,
+   WII5SLEEP_BUTTONS,
+   WII5SLEEP_UPDATE,
+   WII5SLEEP_TIME,
+   WII5SLEEP_COMMS,
+   WII5SLEEP_FINISH
+};
+
+/**
+ * @brief Sleep mode: long sleeps between wake-ups.
+ *
+ * Computes how long to sleep until the next configured wake-up
+ * (capture window, position update, etc.), powers down the Maths CPU
+ * and other peripherals, and uses sh3dNodeUtil.sleep() to put the AVR
+ * into deep sleep.
+ */
+class WII5ModeSleep : public WII5Mode {
+  public:
+		WII5ModeSleep() {}
+    /** @brief Reset to WII5SLEEP_START. */
+    void reset();
+    /** @brief One-time bring-up. */
+    void begin();
+    /** @brief State-machine tick. */
+    void loop();
+
+  protected:
+    bool first;
+    WII5SLEEP_STEPS lastStep;
+    elapsedMillis stepWait;
+    elapsedMillis displayWait;
+    WII5SLEEP_STEPS step;
+    uint32_t sleepNextSeconds;    // How long we going to sleep (cleared after sleep)
+};
+
+extern WII5ModeSleep wii5ModeSleep;
+
+#endif