The Time Synchronization feature is used to retrieve the Intel AMT local time, and to synchronize it against a remote clock. The time in both operations is represented in the UNIX epoch format – the number of seconds elapsed since 01/01/1970 midnight UTC.
Intel AMT uses the BIOS clock as a time reference until AMT_TimeSynchronizationService.SetHighAccuracyTimeSynch is invoked. The sample setup and configuration application in the SDK synchronizes the Intel AMT time as part of the setup and configuration process.
The Intel AMT clock is synchronized using four time measurements:
1. Ta0 - the Intel AMT local time that Intel AMT returns when the user invokes AMT_TimeSynchronizationService.GetLowAccuracyTimeSynch.
2. Tm1 – the remote system time when Ta0 is received.
3. Tm2 – the remote time prior to invoking AMT_TimeSynchronizationService.SetHighAccuracyTimeSynch.
4. Ta3 – the Intel AMT local time when it receives the set command.
When Intel AMT receives the set
request, it notes Ta3 and computes
d = ((Tm1 + Tm2)-(Ta0 + Ta3))/2,
and then sets its local time to (d+Ta3).
In Release 6.0, after performing a manual configuration from the MEBx, Intel AMT will use the local platform clock until the network time is set remotely. When configuration is performed remotely, the platform can continue to use the local clock unless Intel AMT is configured to use Kerberos or TLS. When Kerberos or TLS are enabled, configuration will not complete successfully unless network time was set. Enabling Kerberos and mutual authentication TLS after configuration completion will not succeed if the network time was not set.
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