Building a Stratum-1 GPS Based NTP Server with a Soekris net4501

Taking It One Step Further:

I could have stopped with the hardware mods and had a perfectly normal looking net4501 enclosure (except for the extra BNC connector on the back), but I figured I would take it one step further.

A custom high-performance NTP program, called NTPns, was written by Poul-Henning Kamp specifically for the net4501. Even though NTPns was really designed to run on a modified net4501 that has the stock crystal replaced with a high-stability time source, I figured what the heck. The only two Stratum-0 sources NTPns supports are the DFC77 radio signal (the European equivalent of WWVB) or a Motorola / i-Lotus Oncore GPS receiver. Since I live in the US the radio clock is obviously not going to work for me, but the GPS driver should work just fine.

NTPns also supports the hardware watchdog feature built into the net4501. If the OS locks up or NTPns dies (unlikely, but you never know), the board will reboot. Since the flash drive is mounted read-only, there is no chance for data corruption from a hard reset.

Another nifty feature of NTPns (and another reason why I used it over the reference NTP distribution) is that it supports signaling various conditions via the extra GPIO pins. Connected to the GPIO pins are some extra LEDs, which I mounted on a little prototype board. There are actually like seven LEDs that could be used, but I only built the board for four (three green & one yellow) and modified the code some to use the existing error LED for one of the possible events. This way I do not need to log into the machine or poll it remotely to see what is going on. I can merely glance at the box and determine its status by the LEDs.

So now on the front there are the existing power & network LEDs that function as expected. The error LED will light up if the system does not complete the booting process within 35 seconds. The first custom LED tells me that NTPns is running and able to handle events, the second tells when time is synced and ready to answer NTP requests. The third LED flashes every second, but flashes at different lengths right before and on the exact minute. Finally the last LED lets me know the PLL status, which if locked and everything is normal it should be off.

Above is the final product, while on the outside it might not look like much, it's the inside components that make it special.