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DP83640: How many nanoseconds does it take to arm a PTP trigger?

Part Number: DP83640

Hi, 

The DP83640 can be configured to trigger a GPIO at a specified time, if the specified time is earlier than the current PTP clock time the trigger will fail to arm. 

To allow a trigger to become immediately active the trigger-if-late bit can be set, however I was experiencing issues with this and after further reading I found the following sentence in the software development guide:

Trigger-if-late control - allows immediate trigger if start time is earlier than current clock time (available only for Triggers 0 and 1). Note: This capability is not implemented correctly in revision A1 engineering samples of the DP83640. 

To resolve this problem I determined I could check the current PTP time and if this was later than the time I would like to arm the trigger, I could automatically adjust the time I would like to arm the trigger so it was in the future, to make this happen as soon as possible in the future I need to know how long it would take to arm a PTP trigger in nanoseconds, I guess this will be a certain number of clock cycles but it is not mentioned in the datasheet or software development guide. 

As a side question: Will a PTP trigger be triggered twice if the PTP clock is stepped backwards to a time before a trigger?

Thanks!