Intel® Agilex™ Hard Processor System Technical Reference Manual

ID 683567
Date 11/11/2022
Public

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17.5.2. Timestamp Interface

The timestamp clock reference can come from either the Clock Manager or the FPGA fabric. If the FPGA has implemented the serial capturing of the timestamp interface, then the FPGA must provide the PTP clock reference.

Each EMAC provides its internal timestamp as an output. In some applications, it is advantageous to allow the FPGA fabric access to the Ethernet timestamp. In that case, the timestamp output from each EMAC is sampled in the clk_ptp_ref_i clock domain and serially shifted out to the FPGA fabric. The PTP timestamp clock must be selected to come from the FPGA fabric if the serial timestamp is used in the FPGA.

In addition to providing a timestamp clock reference, the FPGA can monitor the pulse-per-second output from each EMAC module and trigger a snapshot from each auxiliary time stamp timer.

The following table lists the EMAC to FPGA IEEE1588 Timestamp Interface signals to and from each EMAC module.

Table 168.  IEEE 1588 Timestamp Interface Signals (Routed to FPGA I/O)
Signal Name Width Direction Description Default Value for Inputs Recommended Tie-off
emac_ptp_ref_clk 1 Input

Timestamp PTP Clock reference from the fabric.

Used as PTP Clock reference for each EMAC when the fabric has implemented Timestamp capture interface. The timestamp clock is common to all three EMACs. The frequency of this clock can be up to 100 MHz.

1'b1 Pull-up
s2f_emac<2:0>_ptp_tstmp_en 1 Output

Timestamp Serial Interface Enable.

When the local timestamp of each EMAC is sampled, the enable signal is pulsed with the first of 64 bits of serially shifted data. Synchronous to f2h_emac_ptp_ref_clk.

s2f_emac<2:0>_ptp_tstmp_data 1 Output

Timestamp Serial Interface Data.

The 64-bit sampled timestamp is shifted serially to the FPGA fabric from the EMAC. The enable is asserted only on the first bit. The first bit transferred is the least significant bit of the sampled ptp_timestamp[63:0], or ptp_timestamp[0].

emac<2:0>_ptp_pps_o 1 Output

Pulse Per Second Output.

This signal is asserted based on the PPS mode selected in the Register 459 (PPS Control Register). Otherwise, this pulse signal is asserted every time the seconds counter is incremented. This signal is synchronous to f2h_emac_ptp_ref_clk and may only be sampled if the FPGA clock is used as a timestamp reference.

emac<2:0>_ptp_aux_ts_trig_i 1 Input

Auxillary Timestamp Trigger.

This signal is asserted to take an auxiliary snapshot of the time. The rising edge of this internal signal is used to trigger the auxiliary snapshot. The signal is synchronized internally with clk_ptp_ref_i which results in an additional delay of three cycles. This input is asynchronous input and its assertion period must be greater than two PTP active clocks to be sampled.

1'b0 Pull-down

Each EMAC supports either internal or external timestamp reference. In addition, EMAC0 has the option to be the master that provides the timestamp to EMAC1 and EMAC2. In this configuration, EMAC0 must be programmed to select internal timestamp generation in the System Manager and EMAC1 and EMAC2 must be programmed to select external timestamp generation.