[time-nuts] GPSCreations SDR (software defined receiver) GPS1A

Hal Murray hmurray at megapathdsl.net
Thu Jan 20 22:10:30 UTC 2011

> real time processing of *anything* is challenging, even if it's only
> updating once an hour.  I write this because updating once an hour  implies
> you are probably looking at data spanning months, and keeping a  program or
> set of programs reliably running without a hiccup for months  is
> non-trivial.  Sure, we've all got anecdotes of "my machine only  needed to
> be rebooted 6 months ago", but there's a difference between  seeing that in
> the past, and guaranteeing it for the future. 

It should be obvious to anybody who has been working on computers for a 
while, but I still remember how surprised I was when I figured it out.  (That 
was close to 40 years ago.)

  The stability of a system is strongly correlated with how often you change 

Fixing bugs is probably good.  Adding features is not.

It's reasonably easy to get a mature OS to stay up for a long time if you 
aren't asking it to do a lot of work.  So get a separate PC for your data 
collection/control needs.

Assuming your software is solid, somewhere on the scale of a month or a year, 
things like power and/or air-conditioning become the limiting factors.  
(Cleaning up or rearranging your lab may also be significant.)

I've been lucky recently.  My power hasn't gone out for over a year.  They 
upgraded the transformer out front ~5 years ago.  I think it was a lot 
flakier before then, but I don't have any data to back that up.

If your power is flaky, get a UPS.  Be sure to check the numbers.  The 
typical home UPS has a small battery.  It runs long enough to ride over short 
glitches (seconds) and/or let you cleanly save your work and shut things down 
(few minutes), but it won't last hours running a typical PC and display.

If you are interested in long run times on a UPS, consider a low power PC.  
The ones I've seen are generally called "embedded".  They take 1/2 to 1/3 the 
power of of a typical PC at 2x to 3x the cost of a refurbished PC.  Via chips 
are popular.  There are also several very low power ARM systems.

These are my opinions, not necessarily my employer's.  I hate spam.

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