Can not read NTPd timedelta from NMEA device by sysctl hw.sensors.nmea0

[Denis Lapshin]

Hi there!

There is a problem to have time delta from NMEA device with NMEA 0183, 
version 4.0 (V2.3 or V4.1 configurable).

# ldattach -s 9600 nmea /dev/cuaU2
# sysctl hw.sensors.nmea0
hw.sensors.nmea0.indicator0=Off (Signal), UNKNOWN

While connected to cuaU2 by a terminal program all the GPS data seems 
ready and useful.

What the problem could be?

# cat ntpd.conf
sensor nmea0 correction 70000 weight 6 refid GPS stratum 1