The receiver should be configured before starting the NTP daemon, in order to establish reliable position and operating conditions. It does not initiate surveying or hold mode. For use with NTP, the daylight savings time feature should be disables (D0 command) and the broadcast mode set to operate in UTC (BU command).
The timecode format supported by this driver is selected by the poll sequence B5, which initiates a line in the following format to be repeated once per second until turned off by the B0 command.
Format B5 (24 ASCII printing characters):
<cr><lf>i yy ddd hh:mm:ss.000bbb
on-time = <cr>
i = synchronization flag (' ' = locked, '?' = unlocked)
yy = year of century
ddd = day of year
hh:mm:ss = hours, minutes, seconds
.000 = fraction of second (not used)
bbb = tailing spaces for fill
The alarm condition is indicated by a '?' at i, which indicates the receiver
is not synchronized. In normal operation, a line consisting of the timecode
followed by the time quality character (TQ) followed by the receiver status
string (SR) is written to the clockstats file.
The time quality character is encoded in IEEE P1344 standard:
Format TQ (IEEE P1344 estimated worst-case time quality)
0 clock locked, maximum accuracy F clock failure, time not reliable 4 clock unlocked, accuracy < 1 us 5 clock unlocked, accuracy < 10 us 6 clock unlocked, accuracy < 100 us 7 clock unlocked, accuracy < 1 ms 8 clock unlocked, accuracy < 10 ms 9 clock unlocked, accuracy < 100 ms A clock unlocked, accuracy < 1 s B clock unlocked, accuracy < 10 sThe status string is encoded as follows:
Format SR (25 ASCII printing characters)
V=vv S=ss T=t P=pdop E=ee vv = satellites visible ss = relative signal strength t = satellites tracked pdop = position dilution of precision (meters) ee = hardware errorsA three-stage median filter is used to reduce jitter and provide a dispersion measure. The driver makes no attempt to correct for the intrinsic jitter of the radio itself.