Thanks for solution. I encountered the same problem. I use gcc and set noinit "rtt" section on 0x20000000 address, before "data" section. I was looking for a solution all day. in my case when debugging from eclipse RTT viewer worked correctly. but after restarting the power could not find any more. Note: if SEGGERT_RTT has buffers that are not used, they must be forced to zero, otherwise the RTT viewer will not output anything either. memset( &_SEGGER_RTT, 0, sizeof( _SEGGER_RTT) );