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opencomputeproject / Time-Appliance-Project

Develop an end-to-end hypothetical reference model, network architectures, precision time tools, performance objectives and the methods to distribute, operate, monitor time synchronization within data center and much more...
MIT License
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TimeCard starts with a random frequency offset on 10 MHz output #74

Open MaciekMachni opened 2 years ago

MaciekMachni commented 2 years ago

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:

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!

https://user-images.githubusercontent.com/86620984/185916904-a05f1b7f-7723-457e-877f-3e3ee13e429b.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 commented 1 year ago

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