Refactor logger

Author: onkwon

.gitignore

@@ -1,2 +1,4 @@
 build
 .cache
+llvm
+.cscope*

README.md

@@ -0,0 +1,28 @@
+## Directory Structure
+
+```
+.
+├── docs
+├── external
+│   └── libmcu
+├── include
+├── ports
+│   └── esp-idf
+├── src
+└── tests
+    ├── fakes
+    ├── mocks
+    ├── runners
+    ├── src
+    └── stubs
+```
+
+| Directory | Desc.                                                               |
+| --------- | ------------------------------------------------------------------- |
+| docs      | Documentation                                                       |
+| external  | Third-party libraries or SDK. e.g. ESP-IDF                          |
+| include   | The project header files                                            |
+| ports     | Wrappers or glue code to bring third-party drivers into the project |
+| src       | Application code. No hardware or platform-specific code             |
+| tests     | Test codes                                                          |
+

external/libmcu

@@ -0,0 +1,22 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kyunghwan Kwon <k@libmcu.org>
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef LOGGER_H
+#define LOGGER_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include "libmcu/logging.h"
+
+void logger_init(void);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* LOGGER_H */

include/logger.h

@@ -0,0 +1,38 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kyunghwan Kwon <k@libmcu.org>
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "logger.h"
+#include <stdio.h>
+#include "libmcu/board.h"
+
+static size_t logger_writer(const void *data, size_t size)
+{
+	unused(size);
+	static char buf[LOGGING_MESSAGE_MAXLEN];
+	size_t len = logging_stringify(buf, sizeof(buf)-2, data);
+
+	buf[len++] = '\n';
+	buf[len] = '\0';
+
+	const size_t rc = fwrite(buf, len, 1, stdout);
+
+	return rc == 0? len : 0;
+}
+
+static void initialize_backend_stdout(void)
+{
+	static struct logging_backend log_console = {
+		.write = logger_writer,
+	};
+
+	logging_add_backend(&log_console);
+}
+
+void logger_init(void)
+{
+	logging_init(board_get_time_since_boot_ms);
+	initialize_backend_stdout();
+}

include/logging.h

@@ -9,14 +9,12 @@
 #include "libmcu/gpio.h"
 
 #include "pinmap.h"
-#include "logging.h"
+#include "logger.h"
 
 int main(void)
 {
 	board_init(); /* should be called very first. */
-
-	logging_init(board_get_time_since_boot_ms);
-	logging_stdout_backend_init();
+	logger_init();
 
 	const board_reboot_reason_t reboot_reason = board_get_reboot_reason();
 	info("[%s] %s %s", board_get_reboot_reason_string(reboot_reason),