Fix mechanism for OTA upgrade from Sming 4.2 (SmingHub#2728)

* Fix PartitionTable bool() operator

* Allow automatic typecasting from Device::Type to Partition::FullType

* Update documentation

Sming/Components/Storage/README.rst

@@ -91,6 +91,7 @@ When planning OTA updates please check that the displayed partition map correspo
 For example, the partition table requires a free sector so must not overlap other partitions.
 
 Your OTA update process must include a step to write the partition table to the correct location.
+See :doc:`ota-migration`.
 
 It is not necessary to update the bootloader. See :component:`rboot` for further information.
 

Sming/Components/Storage/ota-migration.rst

@@ -0,0 +1,107 @@
+Partition table migration
+=========================
+
+.. highlight:: c++
+
+This guidance applies to esp8266 devices only.
+
+Sming after v4.2 requires a valid partition table.
+If existing devices running previous versions of Sming require updating via OTA then
+an intermediate firmware should be created which installs this partition table.
+
+After rBoot hands control to the SDK entrypoint, the ``user_pre_init()`` function is called.
+This function is documented in the NON-OS-SDK guide and was introduced in version 3.
+It is called by the SDK before user_init() so nothing else in the framework has yet been initialised,
+including any C++ static initialisers.
+
+Sming uses this function to read the partition table into memory.
+Applications may override this function to perform any custom upgrade operations.
+
+Add to application's `component.mk`:
+
+.. code-block:: make
+
+    EXTRA_LDFLAGS := $(call Wrap,user_pre_init)
+    USER_CFLAGS += -DPARTITION_TABLE_OFFSET=$(PARTITION_TABLE_OFFSET)
+
+Add this to your application::
+
+    // Support updating legacy devices without partition tables (Sming 4.2 and earlier)
+    #ifdef ARCH_ESP8266
+
+    namespace
+    {
+    // Note: This file won't exist on initial build!
+    IMPORT_FSTR(partitionTableData, PROJECT_DIR "/out/Esp8266/debug/firmware/partitions.bin")
+    }
+
+    extern "C" void __wrap_user_pre_init(void)
+    {
+        static_assert(PARTITION_TABLE_OFFSET == 0x3fa000, "Bad PTO");
+        Storage::initialize();
+            auto& flash = *Storage::spiFlash;
+        if(!flash.partitions()) {
+            LOAD_FSTR(data, partitionTableData)
+            flash.erase_range(PARTITION_TABLE_OFFSET, flash.getBlockSize());
+            flash.write(PARTITION_TABLE_OFFSET, data, partitionTableData.size());
+            flash.loadPartitions(PARTITION_TABLE_OFFSET);
+        }
+
+        extern void __real_user_pre_init(void);
+        __real_user_pre_init();
+    }
+
+    #endif // ARCH_ESP8266
+
+.. note::
+
+    You will get a 'file not found' error because the partition table gets built *after* compiling the application.
+    You can run ``make partmap-build`` manually first to get around this.
+
+
+An alternative method is to build the partition table layout in code, so there are no external file dependencies::
+
+    // Support updating legacy devices without partition tables (Sming 4.2 and earlier)
+    #ifdef ARCH_ESP8266
+
+    #include <Storage/partition_info.h>
+
+    extern "C" void __wrap_user_pre_init(void)
+    {
+        static_assert(PARTITION_TABLE_OFFSET == 0x3fa000, "Bad PTO");
+
+        Storage::initialize();
+
+        auto& flash = *Storage::spiFlash;
+        if(!flash.partitions()) {
+            using FullType = Storage::Partition::FullType;
+            using SubType = Storage::Partition::SubType;
+    #define PT_ENTRY(name, fulltype, offset, size) \
+        { ESP_PARTITION_MAGIC, FullType(fulltype).type, FullType(fulltype).subtype, offset, size, name, 0 }
+
+            static constexpr Storage::esp_partition_info_t partitionTableData[] PROGMEM{
+                PT_ENTRY("spiFlash", Storage::Device::Type::flash, 0, 0x400000),
+                PT_ENTRY("rom0", SubType::App::ota0, 0x2000, 0xf8000),
+                PT_ENTRY("rom1", SubType::App::ota1, 0x102000, 0xf8000),
+                PT_ENTRY("spiffs0", SubType::Data::spiffs, 0x200000, 0xc0000),
+                PT_ENTRY("spiffs1", SubType::Data::spiffs, 0x2c0000, 0xc0000),
+                PT_ENTRY("rf_cal", SubType::Data::rfCal, 0x3fb000, 0x1000),
+                PT_ENTRY("phy_init", SubType::Data::phy, 0x3fc000, 0x1000),
+                PT_ENTRY("sys_param", SubType::Data::sysParam, 0x3fd000, 0x3000),
+            };
+
+            uint8_t buffer[sizeof(partitionTableData)];
+            memcpy(buffer, partitionTableData, sizeof(partitionTableData));
+            flash.erase_range(PARTITION_TABLE_OFFSET, flash.getBlockSize());
+            flash.write(PARTITION_TABLE_OFFSET, buffer, sizeof(buffer));
+            flash.loadPartitions(PARTITION_TABLE_OFFSET);
+        }
+
+        extern void __real_user_pre_init(void);
+        __real_user_pre_init();
+    }
+
+    #endif // ARCH_ESP8266
+
+
+The above examples are provided as templates and should be modified as required and tested thoroughly!

Sming/Components/Storage/src/include/Storage/Device.h

@@ -40,6 +40,7 @@ class Device : public LinkedObjectTemplate<Device>
 	 * @brief Storage type
 	 */
 	enum class Type : uint8_t {
+		partitionType = uint8_t(Partition::Type::storage),
 #define XX(type, value, desc) type = value,
 		STORAGE_TYPE_MAP(XX)
 #undef XX

Sming/Components/Storage/src/include/Storage/PartitionTable.h

@@ -24,7 +24,7 @@ class PartitionTable
 
 	explicit operator bool() const
 	{
-		return mEntries.isEmpty();
+		return !mEntries.isEmpty();
 	}
 
 	/**