There are two timestamps for NI Automotive Ethernet modules: local and network.Local Timestamp represents the time at which the frame was received by the XNET interface. The timestamp uses the LabVIEW absolute timestamp type .NI Automotive Ethernet modules use PXI_Clk10, a 10 MHz PXI backplane clock provided by the chassis, to drive the local time keeper and to synchronize with other modules in the PXI chassis. If the PXI backplane clock is not available, the module uses its own internal oscillator. PXI_Clk10 provides frequency but not date/time information. When an NI-XNET session is created, XNET initializes the date/time information for the local clock using host time and increment from there off of the 100MHz hardware oscillator. All 4 ports on the same NI Automotive Ethernet modules are initialized simultaneously. If you need to sync hardware timestamps across multiple NI Automotive Ethernet modules, you need to use Future Time Events to get the host times synced up. The local 100MHz oscillator is disciplined by hardware to the PXI_Clk10 backplane clock. The bottom line is that you have 10ns precision for two Ethernet ports on the same NI Automotive Ethernet modules, but you have 100ns for two Ethernet ports on different NI Automotive Ethernet modules (or Ethernet to a CAN card).Network timestamp is timestamp in relation to the 802.1AS grandmaster clock when the 802.1AS network synchronization protocol is used. As stated in the specification for PXIe-852x, the network synchronization accuracy is < 1 µs for 100BASE-T1 and < 3 µs for 1000BASE-T1.
To synchronize frame replay across multiple XNET devices, refer to NI-XNET Hardware and Software Help >> NI-XNET API for LabVIEW >> Appendix >> Additional Information >> Synchronized Replay.
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