[time-nuts] lunatic fringe time standards
magnus at rubidium.dyndns.org
Wed Apr 14 18:11:30 EDT 2010
> Eugen Leitl wrote:
>> Hi -- a couple somewhat lunatic questions. Figured this would
>> be the best place to ask.
>> Anyone aware of a time standard which compensates in regards
>> to an ideal flat-spacetime-at-rest-relatively-to-cosmic-background
>> reference clock? I realize this is not relevant for any affordable
>> Unrelated, anyone aware of a hardware (IC) counter which
>> counts in a (local-bitflip) Gray code, so it can track a very
>> fast (integrated?) oscillator without dropping cycles?
> Any synchronous counter won't drop cycles, right? only ripple carry
> asynchronous have the propagation delay problem.
> However, since long synchronous counters are complex, another way to do
> it is with a linear feedback shift register (LFSR). Rather than doing
> it as usually drawn, with taps all getting xored to generate the single
> feedback, you do it using the output and feeding it "into" the stages
> (with an Xor) where the taps are.
If you want a long synchronous counter, then you can let the lower speed
parts ripple a clock-cycle after the bottom (high-speed) part and delay
the high-speed values with a DFF to bring the values into sync. Takes a
bit of thinking about the details, but you can get about any length of
synchronous result this way. Only problem comes if you reset it, in
which case the reset pulse needs to be applied in a suitably timed
fashion. Repeating this trick and you can get arbitrary lengths of
synchronous length counters.
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