New TIMESTAMPMODE for QPC without system start time #773
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…s are based of the performance counter but do not have a system start time offset applied. Thus, applications can directly convert from QPC (after accounting for frequency) to another time format or source.
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This mode functions the same as
TIMESTAMPMODE_SINGLE_SYNCHRONIZATIONexcept the start time is set to zero. Thus the timestamp appears as "1970-01-01..." in Wireshark for example.This is useful if an application wishes to synchronise packets with an external time source and is able to convert from QPC ticks to that time source. In the regular mode
TIMESTAMPMODE_SINGLE_SYNCHRONIZATION, the driver start time must first be subtracted, which can only be approximated, substantially reducing accuracy. With this modification, high accuracy can be maintained.I've named the new mode
TIMESTAMPMODE_SINGLE_SYNCHRONIZATION_RELATIVEsince the returned timestamps are relative to system boot time, but there may be better names. Similarly, it may be better to pass the timestamp mode into the call toTIME_SYNCHRONIZEand set the timeval to 0 there.