This module is optional, it is present only in the example design when you select 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.
Inputs to this module are 1PPS pulse, serial 1-bit data bus carrying 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 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.