This module is optional and is present only when you select the Enable Ext ToD Bus I/F option while generating the IP. Its function is to load the reference seconds value onto the PTP System Timer and synchronize the System Timer to an external 1PPS source. It is intended to interface with a high precision clock source/timing device.
The inputs to this module are: 1PPS pulse, a serial 1-bit data bus which carries
the reference ToD seconds time that is clocked by a serial clock input. The serial clock
is expected to be less than or equal to the free-running clock (ts_clk) of the Timer Sync block. The process of loading the reference
48-bits second is shown in the following figure.
The External ToD I/F block stores the serial input ToD seconds value in a
holding register. At the next received positive edge of the 1PPS signal, the holding
register’s value is incremented by +1 second, and the result be presented to the PTP
System Timer sub-block. The positive edge of the 1PPS signal is re-timed within the
External ToD I/F block to the ts_clk clock and output
for use by the PTP System Timer block.