I originally installed Armbian_5.38_Orangepizeroplus_Ubuntu_xenial_next_4.14.14
I got NTP with PPS up and running on UART2 with PPS on PA3
I have a working backup image of this.
I then used armbian-config to boot from USB disk and I installed a LAMP stack and battled to get a DB up and running.

My mistake was upgrading the kernel before making a backup.

My version is now ARMBIAN 5.38 stable Ubuntu 16.04.4 LTS 4.14.48-sunxi64
NTP and PPS no longer work.

Is there a way to downgrade the kernel without having to go back to the backup and battle with the DB config again?

I'm a Linux newb so please make allowances for my ignorance.  I have searched for several hours without success before posting.

Having not received a reply to this question, I tried a few things and borked my setup.   I had to go back to my backup on next_4.14.14.  My GPS PPS and NTP Server worked again.

I then plugged in my powered 1TB disk drive and all looked good, until I mounted a partition and began to use it.

The GPS died.  The PPS lock blink went off and obviously NTP stopped receiving PPS and NMEA.  When I stopped using the drive (it was still mounted) the PPS lock blink on the GPS came back and NTP received again.

Very strange.  Is it some kind of USB / UART interference?  Maybe RF interference with the GPS module?  Something related to processor load?

 

Any insight is welcome.

UBLOX 7020 neo-7m-c gnss chip UART TTL level GPS module on UART2 with PPS on PA3

 

You can install specific version this way:

apt install linux-image-next-sunxi64=5.38

But first, check which are available:

apt-cache policy linux-image-next-sunxi64

Why we have a regression here ... hard to say. I assume you have enabled UARTS in armbianEnv.txt ... in case you made changes to DTB, it is overwritten on upgrade.

Thanks Igor,  I have made a note for future reference.

I now suspect that it might not be the higher version causing the problem, but only that the problem is worse and happens all the time on the higher kernel version. 

 

I can make the problem occur on the lower kernel version by copying a very large file on the drive.  If I do the same thing with a usb stick instead of the powered drive, I don't have the problem.  Do you know if there has been a change that could increase power consumption between the two versions?

My thoughts are that there might be a power issue with the drive, even though the drive has it's own power supply and the board is powered by a 3A unit directly connected to the pins.   Next step is to attach a volt-meter to see if I can see a voltage drop or fluctuation.