PR 1704 at https://www.rtems.org/bugzilla/show_bug.cgi?id=1704 suggests that RTEMS support cfsetspeed and cfmakeraw functions for the termios. These functions can be implemented by copying from an implementation with an appropriate license, such as FreeBSD or NetBSD. Note: Linux code cannot be copied into RTEMS because RTEMS is not compatible with the GPL. For this task, you should find implementations of the two functions, and add the implementations into cpukit/libcsupport/src/cfsetspeed.c and cfmakeraw.c, and add the declarations to cpukit/libcsupport/include/sys/termios.h.

Post a patch here, on the Bugzilla, and optionally to the rtems-devel mailing list.