One issue with the clock is that when it cold boots the built in count of the current number of leap second can be wrong until GPS updates the receiver, which happens about every 12 minutes.

It would be ideal if the receiver would update this value whenever it determines that it's wrong. It would only ever do so once the first time the clock starts and once every leap second. But it doesn't currently.

The fantastic news is that this is an operation that we can manually perform with the SkyTraq binary protocol! I found an application note on the Internet, and have used it to add this functionality to the clock. The clock will ask whether the current leap second delta from GPS is valid or not and whether it differs from the default or not. If it is valid and different, an update command is sent to update the default. This action is performed every hour on the half hour.

In addition, at startup the date code of the GPS module firmware is now displayed briefly after the display self-test.

These changes are currently being tested in the v5 clock code, but will be back-ported to all versions of the code.

This obviates the need for the super capacitor on the board, now that I've just had a run of boards manufactured with it installed.

In looking over the binary protocol, it appears that there may be another good idea now that we can speak the binary protocol. GPS works on a 1024 week cycle, which is just short of 20 years. If you don't do anything, then when that 20 week cycle elapses, the date will wrap around to the beginning. This is the GPS version of the Y2K bug. SkyTraq worked around this by declaring a "UTC reference date" and commands to set and retrieve it. The idea is that the 1024 week window is forced to include the reference date near the beginning. If you update the reference date, the 1024 week window will slide forward along with time. It's probably a good idea to set this value once a year. The alternative is to connect a PC up to the serial pins while holding the !RESET line of the controller low and execute the reference date setting command yourself (SkyTraq has a Windows program to do this for you).