/init.harmony.rc
...
# USB GPS pl2303 based
on device-added-/dev/ttyUSB0
    start usbgps

on device-removed-/dev/ttyUSB0
    stop usbgps

service usbgps /system/bin/usbgps.sh
    disabled
    user root

==============================================

/system/bin/usbgps.sh
#!/system/bin/sh
if [ -c /dev/ttyUSB0 ]
then
    stty -F /dev/ttyUSB0 4800
    chmod 0666 /dev/ttyUSB0
fi