talk TSIP to a Trimble Thunderbolt GPS receiver, read PPS pulses, send time to ntpd via "shm" driver.
/etc/ntp.conf should say: server 127.127.28.UNIT mode 1
then run ntp-tsip as: ntp-tsip /dev/cuauX UNIT
includes a hack to fix broken week roll-over in older (pre-E) Thunderbolts.
cc -o tsip tsip.c -lm