I'm using syslog through ITM. In this case syslog_channel function is call before ram initialisation in stm32_clockconfig. But syslog channel uses a global variable that is reset to default by the RAM initialization.

arch/arm/src/efm32/efm32_clockconfig.c

@@ -909,9 +909,6 @@ static inline void efm32_itm_syslog(void)
 
   efm32_enable_auxhfrco();
 
-  /* Then perform ARMv7-M ITM SYSLOG initialization */
-
-  itm_syslog_initialize();
 }
 #else
 #  define efm32_itm_syslog()

arch/arm/src/efm32/efm32_start.c

@@ -275,6 +275,12 @@ void __start(void)
 
   showprogress('C');
 
+#ifdef CONFIG_ARMV7M_ITMSYSLOG
+  /* Perform ARMv7-M ITM SYSLOG initialization */
+
+  itm_syslog_initialize();
+#endif
+
   /* Perform early serial initialization */
 
   up_earlyserialinit();

arch/arm/src/stm32/stm32_start.c

@@ -282,6 +282,12 @@ void __start(void)
 
   showprogress('C');
 
+#ifdef CONFIG_ARMV7M_ITMSYSLOG
+  /* Perform ARMv7-M ITM SYSLOG initialization */
+
+  itm_syslog_initialize();
+#endif
+
   /* Perform early serial initialization */
 
 #ifdef USE_EARLYSERIALINIT

arch/arm/src/stm32/stm32f40xxx_rcc.c

@@ -919,7 +919,6 @@ static inline void rcc_itm_syslog(void)
   modifyreg32(STM32_DBGMCU_CR, DBGMCU_CR_TRACEMODE_MASK, DBGMCU_CR_ASYNCH |
               DBGMCU_CR_TRACEIOEN);
 
-  itm_syslog_initialize();
 }
 #else
 #  define rcc_itm_syslog()