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

I'm backlogged.

DisplayTimeTask.cpp

@@ -0,0 +1,57 @@
+/*
+ * 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.
+ */
+
+#include "DisplayTimeTask.h"
+#include "LowPower.h"
+
+#include "font-notomono-10.h"
+
+
+using Common::ReturnCode;
+using Common::Time;
+using Common::Schedule::NextTime;
+
+DisplayTimeTask::DisplayTimeTask(BSP::DisplayDriver &driver)
+    : m_driver(driver)
+    , m_y_pos(0)
+{}
+
+ReturnCode DisplayTimeTask::init() {
+    return ReturnCode::OK;
+}
+
+NextTime DisplayTimeTask::execute() {
+    //static const char msg_str[] = "Hello world!";
+
+    int x = 20;
+
+    m_driver.clear();
+    m_driver.string_at(x, m_y_pos++, "Hello world!", &font_notomono_10);
+    m_driver.refresh();
+
+    if (m_y_pos > 160) {
+        m_y_pos = 0;
+    }
+
+    BSP::LowPower::stop();
+
+    return NextTime::asap();
+}