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

I'm backlogged.

BlinkTask.h

@@ -0,0 +1,59 @@
+/*
+ * 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 "macros.h"
+
+#include "ReturnCode.h"
+#include "Time.h"
+#include "SystemTime.h"
+
+class BlinkTask : public Common::Schedule::Task {
+public:
+
+    BlinkTask(Common::time_t blink_period)
+        : m_period(blink_period)
+    {}
+
+    Common::ReturnCode init() {
+        /** Enable Port A,B clock */
+        SET(RCC->IOPENR, RCC_IOPENR_IOPBEN);
+        /** Enable pin P3 for output */
+        SET_TO(GPIOB->MODER,
+               GPIO_MODER_MODE3,
+               GPIO_MODER_MODE3_0);
+
+        CLR(GPIOB->OTYPER, GPIO_OTYPER_OT_3);
+        CLR(GPIOB->PUPDR, GPIO_PUPDR_PUPD3);
+
+        return Common::ReturnCode::OK;
+    }
+
+    Common::Schedule::NextTime execute() override {
+        FLIP(GPIOB->ODR, GPIO_ODR_OD3);
+
+        return Common::Schedule::NextTime::in(m_period / 2);
+    }
+
+private:
+    Common::time_t m_period;
+};