This module is optional and is present only when the IP is generated with “Enable Ext ToD Bus I/F” option selected. 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 be interfaced with a high precision clock source/timing device.
The inputs to this module are: 1PPS pulse, serial 1-bit data bus which carries the reference ToD seconds time which 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-bit second is shown in Figure-3.
The External ToD I/F block stores the serially input ToD seconds value in a holding register. At the next received positive edge of the 1PPS signal, the holding register’s value will be incremented by +1 second, and the result be presented to the PTP System Timer sub-block. The positive edge of the 1PPS signal will be retimed within the External ToD I/F block to the ts_clk clock and output output for use by the PTP System Timer block.