logger: Add a Segger RTT backend

Add logger backend that uses Segger RTT for message output. Several
options are provided allowing configuration of up-buffer and logger
behaviour.

Signed-off-by: Pavel Kral <pavel.kral@omsquare.com>

subsys/logging/log_backend_rtt.c

@@ -0,0 +1,202 @@
+/*
+ * Copyright (c) 2018 omSquare s.r.o.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <logging/log_backend.h>
+#include <logging/log_core.h>
+#include <logging/log_msg.h>
+#include <logging/log_output.h>
+#include <rtt/SEGGER_RTT.h>
+
+
+#if CONFIG_LOG_BACKEND_RTT_MODE_DROP
+
+#define DROP_MESSAGE "\nmessages dropped: 99 \r"
+#define DROP_MESSAGE_LEN (sizeof(DROP_MESSAGE) - 1)
+static const char *drop_msg = DROP_MESSAGE;
+static int drop_cnt = 0;
+static int drop_warn = 0;
+
+#else
+
+#define DROP_MESSAGE_LEN 0
+
+#endif /* CONFIG_LOG_BACKEND_RTT_MODE_DROP */
+
+#if CONFIG_LOG_BACKEND_RTT_BUFFER > 0
+static u8_t rtt_buf[CONFIG_LOG_BACKEND_RTT_BUFFER_SIZE];
+#endif /* CONFIG_LOG_BACKEND_RTT_BUFFER > 0 */
+
+static u8_t line_buf[CONFIG_LOG_BACKEND_RTT_MESSAGE_SIZE + DROP_MESSAGE_LEN];
+static u8_t *line_pos;
+static u8_t char_buf;
+static int panic_mode;
+
+static int msg_out(u8_t *data, size_t length, void *ctx);
+
+static int line_out(u8_t data);
+
+static void log_backend_rtt_flush(void);
+
+static int log_backend_rtt_write(void);
+
+static int log_backend_rtt_panic(u8_t *data, size_t length);
+
+static int msg_out(u8_t *data, size_t length, void *ctx)
+{
+	(void) ctx;
+	u8_t *pos;
+
+	if (panic_mode) {
+		return log_backend_rtt_panic(data, length);
+	}
+
+	for (pos = data; pos < data + length; pos++) {
+		if (line_out(*pos)) {
+			break;
+		}
+	}
+
+	return (int) (pos - data);
+}
+
+static int line_out(u8_t data)
+{
+	if (data == '\r') {
+		if (log_backend_rtt_write()) {
+			return 1;
+		}
+		line_pos = line_buf;
+		return 0;
+	}
+
+	if (line_pos < line_buf + sizeof(line_buf) - 1) {
+		*line_pos++ = data;
+	}
+
+	/* not enough space in line buffer, we have to wait for EOL */
+	return 0;
+}
+
+#if CONFIG_LOG_BACKEND_RTT_MODE_DROP
+
+static int log_backend_rtt_write(void)
+{
+	*line_pos = '\r';
+
+	if (drop_cnt > 0 && !drop_warn) {
+		memmove(line_buf + DROP_MESSAGE_LEN, line_buf,
+			line_pos - line_buf);
+		memcpy(line_buf, drop_msg, DROP_MESSAGE_LEN);
+		line_pos += DROP_MESSAGE_LEN;
+		drop_warn = 1;
+	}
+
+	if (drop_warn) {
+		int cnt = min(drop_cnt, 99);
+		if (cnt < 10) {
+			line_buf[DROP_MESSAGE_LEN - 2] = ' ';
+			line_buf[DROP_MESSAGE_LEN - 3] = (u8_t) ('0' + cnt);
+			line_buf[DROP_MESSAGE_LEN - 4] = ' ';
+		} else {
+			line_buf[DROP_MESSAGE_LEN - 2] = (u8_t) ('0' + cnt % 10);
+			line_buf[DROP_MESSAGE_LEN - 3] = (u8_t) ('0' + cnt / 10);
+			line_buf[DROP_MESSAGE_LEN - 4] = '>';
+		}
+	}
+
+	int ret = SEGGER_RTT_WriteSkipNoLock(CONFIG_LOG_BACKEND_RTT_BUFFER,
+					     line_buf, line_pos - line_buf + 1);
+
+	if (!ret) {
+		drop_cnt++;
+		return 0;
+	}
+
+	drop_cnt = 0;
+	drop_warn = 0;
+	return 0;
+}
+
+#elif CONFIG_LOG_BACKEND_RTT_MODE_BLOCK
+
+static int log_backend_rtt_write(void)
+{
+	*line_pos = '\r';
+	if (SEGGER_RTT_WriteSkipNoLock(CONFIG_LOG_BACKEND_RTT_BUFFER, line_buf,
+				       line_pos - line_buf + 1)) {
+		log_backend_rtt_flush();
+		return 0;
+	}
+	return 1;
+}
+
+#endif
+
+static int log_backend_rtt_panic(u8_t *data, size_t length)
+{
+	unsigned int written;
+
+	written = SEGGER_RTT_WriteNoLock(CONFIG_LOG_BACKEND_RTT_BUFFER, data,
+					 length);
+	log_backend_rtt_flush();
+	return written;
+}
+
+
+LOG_OUTPUT_DEFINE(log_output, msg_out, &char_buf, 1);
+
+static void put(const struct log_backend *const backend,
+		struct log_msg *msg)
+{
+	log_msg_get(msg);
+
+	u32_t flags = LOG_OUTPUT_FLAG_LEVEL | LOG_OUTPUT_FLAG_TIMESTAMP;
+
+	if (IS_ENABLED(CONFIG_LOG_BACKEND_SHOW_COLOR)) {
+		flags |= LOG_OUTPUT_FLAG_COLORS;
+	}
+
+	if (IS_ENABLED(CONFIG_LOG_BACKEND_FORMAT_TIMESTAMP)) {
+		flags |= LOG_OUTPUT_FLAG_FORMAT_TIMESTAMP;
+	}
+
+	log_output_msg_process(&log_output, msg, flags);
+
+	log_msg_put(msg);
+
+}
+
+static void log_backend_rtt_init(void)
+{
+	SEGGER_RTT_Init();
+#if CONFIG_LOG_BACKEND_RTT_BUFFER > 0
+	SEGGER_RTT_ConfigUpBuffer(CONFIG_LOG_BACKEND_RTT_BUFFER, "Logger",
+				  rtt_buf, sizeof(rtt_buf),
+				  SEGGER_RTT_MODE_NO_BLOCK_SKIP);
+#endif
+	panic_mode = 0;
+	line_pos = line_buf;
+}
+
+static void panic(struct log_backend const *const backend)
+{
+	panic_mode = 1;
+}
+
+static void log_backend_rtt_flush(void)
+{
+	while (SEGGER_RTT_HasDataUp(CONFIG_LOG_BACKEND_RTT_BUFFER)) {
+		/* pass */
+	}
+}
+
+const struct log_backend_api log_backend_rtt_api = {
+	.put = put,
+	.panic = panic,
+	.init = log_backend_rtt_init,
+};
+
+LOG_BACKEND_DEFINE(log_backend_rtt, log_backend_rtt_api, true);