neocon is a handy terminal application (not only) for u-boot.
neocon has a few graving advantages over some other terminal apps:
Download the source from http://svn.openmoko.org/developers/werner/neocon/ to a directory of your choice and build neocon by issuing
make
To connect to the Bootloader use
./neocon -t 30 /dev/ttyACM0
To getrid of neocon, just issue a
killall neocon