Time-Appliances-Project / Time-Appliances-Project/Time-Card
TimeCard starts with a random frequency offset on 10 MHz output
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- C
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Description
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!
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.
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by tracing the Time Card's boot-time 10MHz output behavior and the GNSS sync monitor path described in the report. Compare startup frequency correction with the moment GNSS lock is acquired, then determine whether retaining corrections or squelching output until initial lock is feasible; done means avoiding the reported out-of-limit drift during locking.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- c
- Domain
- embedded-iot
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 30/100