logging: backend: added semihosting support

subsys/logging/backends/CMakeLists.txt

@@ -74,3 +74,8 @@ zephyr_sources_ifdef(
   CONFIG_LOG_BACKEND_IPC_SERVICE
   log_backend_ipc_service.c
 )
+
+zephyr_sources_ifdef(
+  CONFIG_LOG_BACKEND_SEMIHOST
+  log_backend_semihost.c
+)

subsys/logging/backends/Kconfig

@@ -16,5 +16,6 @@ rsource "Kconfig.swo"
 rsource "Kconfig.uart"
 rsource "Kconfig.xtensa_sim"
 rsource "Kconfig.multidomain"
+rsource "Kconfig.semihost"
 
 endmenu

subsys/logging/backends/Kconfig.semihost

@@ -0,0 +1,30 @@
+# Copyright (c) 2024 Contributors to the logging subsystem.
+# SPDX-License-Identifier: Apache-2.0
+
+config LOG_BACKEND_SEMIHOST
+	bool "Semihost as backend"
+	depends on SEMIHOST
+	select LOG_OUTPUT
+	select LOG_BACKEND_SUPPORTS_FORMAT_TIMESTAMP
+	help
+	  Enable backend in semihost (using host stdout)
+
+if LOG_BACKEND_SEMIHOST
+
+config LOG_BACKEND_SEMIHOST_BUFFER_SIZE
+	int "Size of reserved up-buffer for logger output."
+	default 256
+	help
+	  Specify reserved size of up-buffer used for logger output.
+
+config LOG_BACKEND_SEMIHOST_AUTOSTART
+	bool "Autostart semihost backend"
+	default y
+	help
+	  Enable semihost backend to start automatically.
+
+backend = SEMIHOST
+backend-str = semihost
+source "subsys/logging/Kconfig.template.log_format_config"
+
+endif # LOG_BACKEND_SEMIHOST

subsys/logging/backends/log_backend_semihost.c

@@ -0,0 +1,71 @@
+/* Copyright (c) 2024 Contributors to the logging subsystem.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <stdio.h>
+#include <stddef.h>
+#include <zephyr/logging/log_backend.h>
+#include <zephyr/logging/log_backend_std.h>
+#include <zephyr/logging/log_core.h>
+#include <zephyr/logging/log_output.h>
+#include <zephyr/arch/common/semihost.h>
+
+static uint8_t buf[CONFIG_LOG_BACKEND_SEMIHOST_BUFFER_SIZE];
+static uint32_t log_format_current = CONFIG_LOG_BACKEND_SEMIHOST_OUTPUT_DEFAULT;
+
+static int char_out(uint8_t *data, size_t length, void *ctx)
+{
+	ARG_UNUSED(ctx);
+#define SEMIHOST_STDOUT (1)
+	int ret = semihost_write(SEMIHOST_STDOUT, data, length);
+
+	if (ret) {
+		return ret;
+	}
+
+	return length;
+}
+
+LOG_OUTPUT_DEFINE(log_output_semihost, char_out, buf, sizeof(buf));
+
+static void panic(struct log_backend const *const backend)
+{
+	ARG_UNUSED(backend);
+
+	log_output_flush(&log_output_semihost);
+}
+
+static void dropped(const struct log_backend *const backend, uint32_t cnt)
+{
+	ARG_UNUSED(backend);
+
+	log_output_dropped_process(&log_output_semihost, cnt);
+}
+
+static void process(const struct log_backend *const backend, union log_msg_generic *msg)
+{
+	ARG_UNUSED(backend);
+
+	uint32_t flags = log_backend_std_get_flags();
+
+	log_format_func_t log_output_func = log_format_func_t_get(log_format_current);
+
+	log_output_func(&log_output_semihost, &msg->log, flags);
+}
+
+static int format_set(const struct log_backend *const backend, uint32_t log_type)
+{
+	ARG_UNUSED(backend);
+
+	log_format_current = log_type;
+	return 0;
+}
+
+const struct log_backend_api log_backend_semihost_api = {
+	.process = process,
+	.panic = panic,
+	.dropped = IS_ENABLED(CONFIG_LOG_MODE_IMMEDIATE) ? NULL : dropped,
+	.format_set = format_set,
+};
+
+LOG_BACKEND_DEFINE(log_backend_semihost, log_backend_semihost_api,
+		   IS_ENABLED(CONFIG_LOG_BACKEND_SEMIHOST_AUTOSTART));