[time-nuts] Thought experiment on a low cost timing board

John Pettitt jpp at cloudview.com
Sun Feb 26 18:33:25 EST 2006


Paul Boven wrote:
> Hi everyone,
>
> Poul-Henning Kamp wrote:
>
>   
>> You don't even need 32bits for that:
>>
>> 	http://phk.freebsd.dk/pubs/timecounter.pdf
>>
>> And doing it in hardware would be more expensive than in software, hardware
>> access is much slower than memory access.
>>     
>
> How about taking one of the bigger FPGA's, that can hold a complete 
> stand-alone microcontoller, running a Unix-like OS? You could implement 
> several fast, wide synchronous counter/latches in the same FPGA fabric, 
> so there would be no need to bother with things like PCI busses. Does 
> FreeBSD run on any of these chips?
>
> With a serial (for NMEA) and PPS input, and ethernet output, you'd have 
> an NTP-server-on-a-chip. Add a D/A-converter to discipline a TCXO, and 
> you're all set. An FPGA with relatively few pins, hence no BGA, would 
> suffice. Building such a device would be within the capabilities of some 
> of the more dedicated timenuts in here.
>
> Regards, Paul Boven - PE1NUT
>
>
>
>   
I seriously thought about that - if you go that route you rapidly end up
with a Sokeris board with timing control added which is pretty much
where I started.  It would be fun to build a single chip ntp box but the
development effort is substantial.

I'm not married to the PCI approach but I do need to be able to read the
counters in a predictable time and PCI (or some other bus) seems to be
the only way to do that.   There are some great FPGA demo boards with
USB on them but USB is so unpredictable that it defeats the object.

John - W6/G6KCQ




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