Understanding training patterns for Stratix-II deserializer DPA

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As for a training pattern, I've heard pretty much anything with transitions will work, but with fewer transitions it may just take longer. It is not looking for a pattern though(such as 10-bit comma), just transitions to figure out where the data changes and where to center the clock.

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That's what I, too, thought would be logical.

However I see different behavior in the field. Sometimes it looks like after achieving initial lock a DPA machine completely stops tracking [very slow in my case] data phase changes. That despite transmitted data containing significant number of transitions.