Today we saw a weird issue with the GPS receiver (EndRun Technologies Tempus LX). GPS timing on fb1 (which is handled via IRIG-B connection to the receiver with a spectracom card) was off by +18 seconds. We tried resetting the GPS receiver and it still came up with +18 second offset. To be clear, the GPS receiver unit itself was showing a time on it's front panel that looked close enough to 24-hour UTC, but was off by +18s. The time also said "GPS" vertically to the right of the time.
We started exploring the settings on the GPS receiver and found this menu item:
Clock -> "Time Mode" -> "UTC"/"GPS"/"Local"
The setting when we found it was "GPS", which seems logical enough. However, when we switched it to "UTC" the time as shown on the front panel was correct, now with "UTC" vertically to the right of the time, and fb1 was then showing the correct GPS time.
From the manual:
The fact that moving to "UTC" fixed the problem, even though that is supposed to remove the leap second correction, might indicate that there's another bug in the symmetricom driver...