[time-nuts] Thought experiment on a low cost timing board
jpp at cloudview.com
Sat Feb 25 18:50:56 EST 2006
Tim Shoppa wrote:
> Hal Murray <hmurray at suespammers.org> wrote:
>>> PCI 3.3v board with:
>>> 10Mhz OCXO (provision for external clock source?)
>>> Uart (serial is an endangered on many PC's)
>>> Free running counter driven from the OCXO and readable by PC
>>> inputs to latch the counter (how many?) with the latched result
>>> also readable (for PPS)
>> I've been daydreaming along the same line but haven't hit a combination of
>> ideas that feels good enough to actually do anything.
>> My list has a FPGA in the middle. The problem with that is that newer FPGAs
>> don't work on 5V PCI which is what all of my PCs have. The only 3V slots
>> I've seen are in high end (noisy, expensive) servers. The PCI slots on
>> Soekris boards are 3V. That adds another option to think about.
>> There are several possibilities for dealing with 5V PCI.
>> [ BGA's, Gold Fingers, etc.]
> My gut feeling: back up a little bit. Figure out how to do what you
> want without a PCI bus, without gold fingers, without BGA's, etc.
I had several goals in mind when I asked the initial question:
1) a low cost high stability ntp stratum 1 clock board - something that
when added to a sub $100 gps would yield a really stable time source for
ntp. To do this it really needs to let the main cpu read the counters
in a predictable, consistent time which is why I wanted PCI (3v because
I have soekris boxes).
2) it would also be nic to be able to add a low cost frequency synth to
What I've seen so far there are designs out there based on various cpu
cores and or f/c pga chips that are close to what I'm thinking. The
replies from the list have been really helpful - I'm going to do some
more research and look closely at the existing designs and see what I
What prompted this in the first place was the horrible temperature
sensitivity my soekris boxes exhibit - I can only keep them to within
10us of the gps 95% of the time and the occasional 100us excursion is
not uncommon. I want to be stable to the limit of the gps I'm using -
for no other reason than the belief that I can do it for way less than
commercial devices using open source software and low cost hardware. In
other works I'm hacking for the sake of it :-)
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