RTEMS can send its syslog messages over Ethernet, apparently with a protocol close to (or compliant with) RFC 5424. This is an undocumented feature of RTEMS.
Simply setting the log_host parameter to an IP address string in the rtems_bsdnet_config structure does not work. The UDP packet is apparently sent in the vsyslog function from cpukit/libnetworking/lib/syslog.c.
This would enable a printf-like feature over Ethernet, without the need to open the box to connect a serial cable.