[ext] example for json usage added

examples/nucleo_g474re/json/main.cpp

@@ -0,0 +1,186 @@
+/*
+ * Copyright (c) 2024, Henrik Hose
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <modm/board.hpp>
+#include <modm/debug/logger.hpp>
+#include <nlohmann-json/json.hpp>
+
+#undef MODM_LOG_LEVEL
+#define MODM_LOG_LEVEL modm::log::INFO
+
+// ----------------------------------------------------------------------------
+
+extern "C" const uint32_t __rom_end[];
+using json = nlohmann::json;
+
+constexpr auto max_flash_pages{64};
+
+namespace data
+{
+struct person
+{
+	std::string name;
+	float height;
+	int age;
+	auto
+	operator<=>(const person&) const = default;
+};
+
+void
+to_json(json& j, const person& p)
+{
+	j = json{{"name", p.name}, {"height", p.height}, {"age", p.age}};
+}
+
+void
+from_json(const json& j, person& p)
+{
+	j.at("name").get_to(p.name);
+	j.at("height").get_to(p.height);
+	j.at("age").get_to(p.age);
+}
+}  // namespace data
+
+int
+main()
+{
+	Board::initialize();
+
+	MODM_LOG_INFO << "\n\n+++++++++++++++++++++++++++" << modm::endl;
+	MODM_LOG_INFO << "++ NLOHMANN JSON example ++" << modm::endl;
+	MODM_LOG_INFO << "+++++++++++++++++++++++++++\n" << modm::endl;
+
+	// data::person alice_struct = {"Alice", 50};
+	data::person alice_struct = {"Alice", 1.85, 50};
+	json alice_json = alice_struct;
+
+	// basic JSON character string usage
+	{
+		auto alice_json_string = alice_json.dump();
+
+		// imagine that we transmit this string over some interface
+		MODM_LOG_INFO << "JSON from struct is: " << alice_json_string.c_str() << modm::endl;
+
+		// and now we can retrieve the struct from the json object
+		json retrieved_alice_json = json::parse(alice_json_string);
+
+		// JSON is fairly self-annotated, so we might not even need the original struct
+		MODM_LOG_INFO << "\nRetrieved from string JSON has fields ... ";
+		for (auto& [key, value] : retrieved_alice_json.items())
+		{
+			MODM_LOG_INFO << key.c_str() << ", ";
+		}
+		MODM_LOG_INFO << modm::endl;
+		MODM_LOG_INFO.flush();
+
+		// check if retrieved struct is same
+		auto retrieved_alice_struct = retrieved_alice_json.template get<data::person>();
+		if (retrieved_alice_struct == alice_struct)
+		{
+			MODM_LOG_INFO << "\nRetrieved from string and original struct are identical"
+						  << modm::endl;
+		}
+		MODM_LOG_INFO.flush();
+	}
+
+	// basic binary JSON usage
+	{
+		// convert to BSON
+		auto alice_binary = json::to_bson(alice_json);
+
+		MODM_LOG_INFO << "\nBinary JSON (BSON): ";
+		for (const auto& byte : alice_binary) { MODM_LOG_INFO.printf(" 0x%02x", byte); }
+		MODM_LOG_INFO << modm::endl;
+
+		// put BSON in first flash page after program
+		uint32_t err{0};
+		const size_t page_start = Flash::getPage(reinterpret_cast<uint32_t>(&__rom_end)) + 1;
+		const size_t num_bytes = alice_binary.size();
+		const size_t flash_page_size = Flash::getSize(page_start);
+		const size_t end_page = page_start + (num_bytes + flash_page_size - 1) / flash_page_size;
+		if (end_page >= max_flash_pages)
+		{
+			MODM_LOG_ERROR << "\nRequested flash end page exceeds flash [" << page_start << ", "
+						   << end_page << ")" << modm::endl;
+			MODM_LOG_INFO.flush();
+			while (1);
+		}
+
+		// erase the pages before programming
+		MODM_LOG_INFO << "\nErasing flash sectors [" << page_start << ", " << end_page << ")"
+					  << modm::endl;
+		MODM_LOG_INFO.flush();
+		if (not Flash::unlock())
+		{
+			MODM_LOG_INFO << "Flash unlock failed!" << modm::endl;
+			while (1);
+		}
+		for (size_t page{page_start}; page < end_page; page++) err |= Flash::erase(page);
+		if (err != 0)
+		{
+			MODM_LOG_ERROR << "\nThere was an error while erasing flash!" << modm::endl;
+			MODM_LOG_INFO.flush();
+			while (1);
+		}
+
+		// pad the data with zeros to fit flash words
+		size_t unpadded_size{alice_binary.size()};
+		size_t word_size{sizeof(Flash::MaxWordType)};
+		if (auto padding = (word_size - unpadded_size % word_size) % word_size; padding > 0)
+		{
+			alice_binary.resize(alice_binary.size() + padding, 0);
+		}
+
+		// now, write the padded data
+		MODM_LOG_INFO << "\nWriting, word size: " << word_size
+					  << ", num of bytes (payload): " << unpadded_size
+					  << ", num of bytes (padded): " << alice_binary.size() << "... ";
+
+		for (uint32_t src_addr = reinterpret_cast<uint32_t>(&alice_binary[0]),
+					  dst_addr{reinterpret_cast<uint32_t>(Flash::getAddr(page_start))};
+			 src_addr < (reinterpret_cast<uint32_t>(&alice_binary[0]) + alice_binary.size());
+			 src_addr += sizeof(Flash::MaxWordType), dst_addr += sizeof(Flash::MaxWordType))
+		{
+			err |= Flash::program(dst_addr, *(Flash::MaxWordType*)src_addr);
+		}
+		if (err != 0)
+		{
+			MODM_LOG_ERROR << "\nThere was an error while programming flash!" << modm::endl;
+			MODM_LOG_INFO.flush();
+			while (1);
+		}
+		MODM_LOG_INFO << "Writing complete! " << modm::endl;
+		MODM_LOG_INFO.flush();
+
+		// we can now read BSON back from flash, first 4 bytes entry is the size
+		uint32_t read_len = *(reinterpret_cast<uint32_t*>(Flash::getAddr(page_start)));
+
+		// read the actual data
+		MODM_LOG_INFO << "\nReading BSON of size " << read_len << " from flash: ";
+		auto raw_bytes =
+			std::vector<uint8_t>(Flash::getAddr(page_start), Flash::getAddr(page_start) + read_len);
+		for (const auto& byte : raw_bytes) { MODM_LOG_INFO.printf(" 0x%02x", byte); }
+		MODM_LOG_INFO << modm::endl;
+		MODM_LOG_INFO.flush();
+
+		// reconstruct the data
+		auto retrieved_alice_json = json::from_bson(raw_bytes);
+		auto retrieved_alice_struct = retrieved_alice_json.template get<data::person>();
+		if (retrieved_alice_struct == alice_struct)
+		{
+			MODM_LOG_INFO << "\nRetrieved from flash and original struct are identical"
+						  << modm::endl;
+		}
+		MODM_LOG_INFO.flush();
+	}
+
+	while (1);
+	return 0;
+}

examples/nucleo_g474re/json/project.xml

@@ -0,0 +1,13 @@
+<library>
+  <extends>modm:nucleo-g474re</extends>
+  <options>
+    <option name="modm:build:build.path">../../../build/nucleo_g474re/json</option>
+  </options>
+  <modules>
+    <module>modm:debug</module>
+    <module>modm:platform:gpio</module>
+    <module>modm:platform:flash</module>
+    <module>modm:nlohmann-json</module>
+    <module>modm:build:scons</module>
+  </modules>
+</library>