TimeCard starts with a random frequency offset on 10 MHz output

[MaciekMachni]

Time Card starts with a random frequency offset (around 5ppm).
It doesn't correct the frequency until it gets the GNSS lock.

The issue is shown in the video below. It shows two traces:

• yellow: 10MHz from a PTP source synchronized to the GNSS signal
• green: 10MHz output of the Time Card.

Timestamps:
0:00 - boot and enable gnss_sync monitor
1:35 - GNSS sync acquired
4:20 - pull-in begins
5:11 - biggest frequency drift
5:14 - lock acquired

Just before the lock, the frequency drifts to ~ -20 ppm!

2022-08-22.13-41-29-cut.3.mp4

If this behavior is unavoidable (i.e., saving the last corrections and applying them on boot), there should be an option to squelch 10MHz output until it gets the initial lock, as in the current state, it breaks the 4.6 ppm limits of SyncE while locking.

[ahmadexp]

Perhaps that is because it that point the internal XTAL on the SOM is in use.