C++ refactoring, plus low-power support, plus software-based SPI CS

I'm backlogged.

Time.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2019  Max Regan
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+namespace Common {
+
+using time_t = uint64_t;
+
+class Time {
+public:
+    static constexpr uint64_t MILLIS_PER_SEC = 1e3;
+    static constexpr uint64_t MICROS_PER_SEC = 1e6;
+    static constexpr uint64_t NANOS_PER_SEC  = 1e9;
+
+    static constexpr uint64_t MICROS_PER_MILLI = 1e3;
+    static constexpr uint64_t NANOS_PER_MILLI  = 1e6;
+
+    static constexpr uint64_t NANOS_PER_MICRO = 1e3;
+
+    static inline time_t nanos(uint64_t value)
+    {
+        return value / NANOS_PER_MICRO;
+    }
+
+    static inline time_t micros(uint64_t value)
+    {
+        return value;
+    }
+
+    static inline time_t millis(uint64_t value)
+    {
+        return value * MICROS_PER_MILLI;
+    }
+
+    static inline time_t seconds(uint64_t value)
+    {
+        return value * MICROS_PER_SEC;
+    }
+};
+
+}