[time-nuts] An embedded NTP server

[Michael Tharp]

On 01/02/2013 08:34 PM, Tom Harris wrote:
> Do you really need an OS? Surely for a box that is only ever going to be an
> NTP server you just need a network interface and good maths? I've just seen
> a later comment where you mention floating point support, but would 64 bit
> integer maths work just as well?

You certainly do not need an OS. For this project I am using a RTOS 
called ChibiOS that provides a threading interface and handles the 
tedium of flinging packets as well as timers, serial, etc. but it's not 
an OS in the same sense as Linux is and I'm still interacting directly 
with the critical peripherals.

Since the PPS measurements are being done in dedicated hardware and the 
Ethernet interface is a hard-wired MAC and not USB, it performs quite a 
bit better than something with the overhead of a managed OS. Raspberry 
Pi and some other Linux-ready boards I've seen also use Ethernet 
interfaces built into the USB host, not quite sure why that's more 
cost-effective but it's sure to result in much poorer jitter versus a 
direct MAC.

I'm using a F1 part which does not have a FPU, so all the math is 64bit 
integers. Soft floats are also an option, and for even the fanciest 
GPSDO there's not nearly enough number crunching going on to make a FPU 
absolutely necessary.