using phc2sys, there is a fixed 0.5ms offset between the system time and phc time

[zhupidong]

hi:
I want to set system time with phc time.
Use the following command：

1. ts2phc -f ts2phc.cfg -m -s nmea -l 7
2. phc2sys -d /dev/pps0 -s dpni.0 -c CLOCK_REALTIME -m -O 0 -S 5

phc2sys output is
phc2sys[62092.093]: CLOCK_REALTIME pps offset -1158 s2 freq -3041
phc2sys[62093.093]: CLOCK_REALTIME pps offset 643 s2 freq -1587
phc2sys[62094.093]: CLOCK_REALTIME pps offset 391 s2 freq -1647
phc2sys[62095.093]: CLOCK_REALTIME pps offset 917 s2 freq -1003
phc2sys[62096.093]: CLOCK_REALTIME pps offset -1159 s2 freq -2804
phc2sys[62097.093]: CLOCK_REALTIME pps offset -395 s2 freq -2388
phc2sys[62098.093]: CLOCK_REALTIME pps offset 313 s2 freq -1798
phc2sys[62099.093]: CLOCK_REALTIME pps offset -168 s2 freq -2185
phc2sys[62100.093]: CLOCK_REALTIME pps offset -543 s2 freq -2611
phc2sys[62101.093]: CLOCK_REALTIME pps offset 629 s2 freq -1602
phc2sys[62102.093]: CLOCK_REALTIME pps offset 510 s2 freq -1532
phc2sys[62103.093]: CLOCK_REALTIME pps offset -557 s2 freq -2446
phc2sys[62104.093]: CLOCK_REALTIME pps offset 809 s2 freq -1247
phc2sys[62105.093]: CLOCK_REALTIME pps offset 1656 s2 freq -157
phc2sys[62106.093]: CLOCK_REALTIME pps offset -2026 s2 freq -3343
phc2sys[62107.093]: CLOCK_REALTIME pps offset -443 s2 freq -2367
phc2sys[62108.093]: CLOCK_REALTIME pps offset -435 s2 freq -2492
phc2sys[62109.093]: CLOCK_REALTIME pps offset -223 s2 freq -2411
phc2sys[62110.093]: CLOCK_REALTIME pps offset 628 s2 freq -1627
phc2sys[62111.093]: CLOCK_REALTIME pps offset 695 s2 freq -1371
phc2sys[62112.093]: CLOCK_REALTIME pps offset -693 s2 freq -2551
phc2sys[62113.093]: CLOCK_REALTIME pps offset -782 s2 freq -2848
phc2sys[62114.093]: CLOCK_REALTIME pps offset 906 s2 freq -1394
phc2sys[62115.093]: CLOCK_REALTIME pps offset 460 s2 freq -1569
phc2sys[62116.093]: CLOCK_REALTIME pps offset -651 s2 freq -2542
phc2sys[62117.093]: CLOCK_REALTIME pps offset 131 s2 freq -1955
phc2sys[62118.093]: CLOCK_REALTIME pps offset -34 s2 freq -2081
phc2sys[62119.093]: CLOCK_REALTIME pps offset 1167 s2 freq -890
phc2sys[62120.093]: CLOCK_REALTIME pps offset -983 s2 freq -2690

but when I use the testptp to calculate the offset between system time and phc, I find that there is a fixed 0.5ms offset between the system time and phc time

[root@aarch64 /home/user/zjl]# ./testptp -k 3
system and phc clock time offset request okay
system time: 1667874466.435949440
phc time: 1667874466.436529180
system time: 1667874466.435963000
system/phc clock time offset is -572960 ns
system clock time delay is 13560 ns
system time: 1667874466.435963000
phc time: 1667874466.436530510
system time: 1667874466.435964320
system/phc clock time offset is -566850 ns
system clock time delay is 1320 ns
system time: 1667874466.435964320
phc time: 1667874466.436531790
system time: 1667874466.435965720
system/phc clock time offset is -566770 ns
system clock time delay is 1400 ns

How to eliminate this deviation,thank you.