syslog: CONFIG_CLOCK_MONOTONIC

drivers/syslog/Kconfig

@@ -116,6 +116,15 @@ config SYSLOG_TIMESTAMP
 	---help---
 		Prepend timestamp to syslog message.
 
+config SYSLOG_TIMESTAMP_REALTIME
+	bool "Use wall-clock for syslog timestamp"
+	default n
+	depends on SYSLOG_TIMESTAMP
+	---help---
+		Use wall-clock (CLOCK_REALTIME) for timestamp.  By default,
+		CLOCK_MONOTONIC, if enabled, will be used or the system timer
+		is not.
+
 config SYSLOG_SERIAL_CONSOLE
 	bool
 	default n

drivers/syslog/vsyslog.c

@@ -82,13 +82,21 @@ int _vsyslog(int priority, FAR const IPTR char *fmt, FAR va_list *ap)
   ret = -EAGAIN;
   if (OSINIT_HW_READY())
     {
+#if defined(CONFIG_SYSLOG_TIMESTAMP_REALTIME)
+      /* Use CLOCK_REALTIME if so configured */
+
+      ret = clock_gettime(CLOCK_REALTIME, &ts);
+
+#elif defined(CONFIG_CLOCK_MONOTONIC)
       /* Prefer monotonic when enabled, as it can be synchronized to
        * RTC with clock_resynchronize.
        */
 
-#ifdef CONFIG_CLOCK_MONOTONIC
       ret = clock_gettime(CLOCK_MONOTONIC, &ts);
+
 #else
+      /* Otherwise, fall back to the system timer */
+
       ret = clock_systimespec(&ts);
 #endif
     }