The RTEdbg open source toolkit helps embedded developers test, debug, 
and optimize C/C++ firmware. It provides functions for non-intrusive 
data logging, data transfer to host, and decoding utilities that enable 
deeper insight into real-time systems. Unlike traditional debuggers, 
this solution doesn't stop the embedded system, preserving its natural 
behavior. It's suitable for large RTOS-based systems as well as small, 
resource-constrained systems. The solution is the equivalent of a 
re-entrant, time-stamped fprintf() running on the host instead of the 
embedded system. The fprintf functionality provides flexibility in data 
formatting and allows the logging data to be sorted into multiple files 
for later analysis with common tools such as CSV and LOG readers.

See: https://github.com/RTEdbg/RTEdbg