driver::storage::Flash: FlashAsStorage-based storage component

This is a primitive implementation of a `FlashAsStorage` (or rather,
`FlashAsEEPROM`)-based storage component. It's based on `FlashAsEEPROM`, because
I couldn't find a sane way to push the storage data variable within our template
class.

At some point, this needs to be reworked, to pull the size from Props, and not
use the EEPROM API wrappers.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/kaleidoscope/driver/storage/Flash.h

@@ -0,0 +1,80 @@
+/* -*- mode: c++ -*-
+ * kaleidoscope::driver::storage::Flash -- Storage driver with Flash backend
+ * Copyright (C) 2019  Keyboard.io, Inc
+ * Copyright (C) 2019  Dygma Lab S.L.
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * TODO(algernon): This currently uses <FlashAsEEPROM.h>, making the Props
+ * struct fairly useless. At some point, we need to figure out a way to do this
+ * without EEPROM API emulation, and by having the flash data variable somewhere
+ * within the `storage::Flash` class.
+ */
+
+#pragma once
+
+#ifdef __SAMD21G18A__
+
+#include "kaleidoscope/driver/storage/Base.h"
+#include <FlashStorage.h>
+#include <FlashAsEEPROM.h>
+
+// We need to undefine Flash, because `FlashStorage` defines it as a macro, yet,
+// we want to use it as a class name.
+#undef Flash
+
+namespace kaleidoscope {
+namespace driver {
+namespace storage {
+
+struct FlashProps : kaleidoscope::driver::storage::BaseProps {
+  static constexpr uint16_t length = EEPROM_EMULATION_SIZE;
+};
+
+template <typename _StorageProps>
+class Flash: public kaleidoscope::driver::storage::Base<_StorageProps> {
+ public:
+  template<typename T>
+  T& get(uint16_t offset, T& t) {
+    return EEPROM.get(offset, t);
+  }
+
+  template<typename T>
+  const T& put(uint16_t offset, T& t) {
+    EEPROM.put(offset, t);
+  }
+
+  uint8_t read(int idx) {
+    return EEPROM.read(idx);
+  }
+
+  void write(int idx, uint8_t val) {
+    EEPROM.write(idx, val);
+  }
+
+  void update(int idx, uint8_t val) {
+    EEPROM.update(idx, val);
+  }
+
+  void commit() {
+    EEPROM.commit();
+  }
+};
+
+}
+}
+}
+
+#endif