gmacgrp_pps_control

         Controls timestamp Pulse-Per-Second output
Module Instance Base Address Register Address
i_emac_emac0 0xFF800000 0xFF80072C
i_emac_emac1 0xFF802000 0xFF80272C
i_emac_emac2 0xFF804000 0xFF80472C

Offset: 0x72C

Access: RW

Important: The value of a reserved bit must be maintained in software. When you modify registers containing reserved bit fields, you must use a read-modify-write operation to preserve state and prevent indeterminate system behavior.
Bit Fields
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

Reserved
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Reserved

trgtmodsel0

RW 0x0

ppsen0

RW 0x0

ppsctrl_ppscmd

RW 0x0

gmacgrp_pps_control Fields

Bit Name Description Access Reset
6:5 trgtmodsel0 
This field indicates the Target Time registers (register 455 and 456) mode for PPS0 output signal
Value Description
0x0 TRGTINTERONLY
0x2 TRGTINTPPS0
0x3 TRGTNOINTER
RW 0x0
4 ppsen0 
When set low, Bits[3:0] function as PPSCTRL (backward compatible). When set high, Bits[3:0] function as PPSCMD.
Value Description
0x0 PPSCTRL
0x1 PPSCMD
RW 0x0
3:0 ppsctrl_ppscmd

PPSCTRL0: PPS0 Output Frequency Control

This field controls the frequency of the PPS0 output (ptp_pps_o[0]) signal. The default value of PPSCTRL is 0000, and the PPS output is 1 pulse (of width clk_ptp_i) every second. For other values of PPSCTRL, the PPS output becomes a generated clock of following frequencies:

  • 0001: The binary rollover is 2 Hz, and the digital rollover is 1 Hz.
  • 0010: The binary rollover is 4 Hz, and the digital rollover is 2 Hz.
  • 0011: The binary rollover is 8 Hz, and the digital rollover is 4 Hz.
  • 0100: The binary rollover is 16 Hz, and the digital rollover is 8 Hz.
  • ...
  • 1111: The binary rollover is 32.768 KHz, and the digital rollover is 16.384 KHz.
Note: In the binary rollover mode, the PPS output (ptp_pps_o) has a duty cycle of 50 percent with these frequencies.

In the digital rollover mode, the PPS output frequency is an average number. The actual clock is of different frequency that gets synchronized every second. For example:

  • When PPSCTRL = 0001, the PPS (1 Hz) has a low period of 537 ms and a high period of 463 ms
  • When PPSCTRL = 0010, the PPS (2 Hz) is a sequence of:
    • One clock of 50 percent duty cycle and 537 ms period>
    • Second clock of 463 ms period (268 ms low and 195 ms high)
  • When PPSCTRL = 0011, the PPS (4 Hz) is a sequence of:
    • Three clocks of 50 percent duty cycle and 268 ms period
    • Fourth clock of 195 ms period (134 ms low and 61 ms high)

This behavior is because of the non-linear toggling of bits in the digital rollover mode in Register 451 (System Time - Nanoseconds Register).

Flexible PPS0 Output (ptp_pps_o[0]) Control

Programming these bits with a non-zero value instructs the MAC to initiate an event. Once the command is transferred or synchronized to the PTP clock domain, these bits get cleared automatically. The Software should ensure that these bits are programmed only when they are all-zero. The following list describes the values of PPSCMD0:

  • 0000: No Command
  • 0001: START Single Pulse

    This command generates single pulse rising at the start point defined in Target Time Registers (register 455 and 456) and of a duration defined in the PPS0 Width Register.

  • 0010: START Pulse Train

    This command generates the train of pulses rising at the start point defined in the Target Time Registers and of a duration defined in the PPS0 Width Register and repeated at interval defined in the PPS Interval Register. By default, the PPS pulse train is free-running unless stopped by 'STOP Pulse train at time' or 'STOP Pulse Train immediately' commands.

  • 0011: Cancel START

    This command cancels the START Single Pulse and START Pulse Train commands if the system time has not crossed the programmed start time.

  • 0100: STOP Pulse train at time

    This command stops the train of pulses initiated by the START Pulse Train command (PPSCMD = 0010) after the time programmed in the Target Time registers elapses.

  • 0101: STOP Pulse Train immediately

    This command immediately stops the train of pulses initiated by the START Pulse Train command (PPSCMD = 0010).

  • 0110: Cancel STOP Pulse train

    This command cancels the STOP pulse train at time command if the programmed stop time has not elapsed. The PPS pulse train becomes free-running on the successful execution of this command.

  • 0111-1111: Reserved
 RW 0x0