The issue of /dev/pps1

Recently I used the instruction in the weblink:Enabling PPS on Jetson Nano.
I successfully reflshed the kernel of the Jetson Nano, and after reflashing, Jetson Nano boot automatically, and when I input: ls /dev/pps* it can show: /dev/pps0 and /dev/pps1, but when I reboot the jetson nano it can only show the /dev/pps0. I do not know what is wrong but I guess maybe it is the problem of device tree setup? I will appreciate if you can give me some advices. Thx!

Could you reference to this topic.