Meinberg M900, Operating Instructions Manual, Page: 27 / 170

Functionality in Master Systems
After power up, the module accepts the absolute time information (PTP seconds) of a
reference time source (GPS controlled clock) once only and the PTP nanoseconds are
set to zero. If the oscillator frequency of the reference time source has reached it‘s
nominal value, resetting of the nanoseconds is repeated. This procedure leads to a
maximum deviation of 20 nsec of the pulse per second (PPS) of the PTP Master
compared to the PPS of the GPS controlled clock. The reference clock of TSU-V2 (50
MHz) is derived from the GPS disciplined oscillator of the reference time source by
using a PLL (
P hase L ocked L oop) of the FPGA. The direct coupling of the time
stamp unit to the GPS system is achieved in this way.
Functionality in Slave Systems
After decoding a valid time information from a PTP Master, the system sets it‘s own
PTP seconds a nanoseconds accordingly. The PTP offset calculated by the PTP driver
software of the single board computer is used for adjustment of the master oscillator
of TSU-V2. High accuracy of the output signals (10 MHz/PPS/IRIG) generated by
the PTP Slave is achieved this way.
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