| Re: modulo reset [message #41846 is a reply to message #41700] |
Tue, 23 November 2004 10:51  |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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Ralf Schaa wrote:
...
> I am reading binary data (not longer than 32 bit, and I store it in ULL
> as suggested)
> and the 'modulo reset' I talked about may appear at one datafield: that
> is in an accumulated
> "Doppler" cycle count.
> By differentiating with respect to time, one can get the true doppler
> count.
"Differencing", not "Differentiating". You differentiate a continuous
function of time. For a discontinuously sampled function, you can't
differentiate, you can only calculate finite differences.
> Than the documentation says, when a modula reset occurs , add 2^32.
> I think, this means when the counter is full and is starting with zero
> again. than add the 2^32.
> But I don't see what adding 2^32 exactly would do ...
Let's assume that the current cycle count is t0=2^32-5. 20 cyles later
the true count would be 2^32+15. However, because it reset at 2^32, the
actual number in the cycle count would be t1=15. If you calculate the
time difference as dt = t1-t2 while storing the value in, for instance,
a 64 byte integer or floating point type, then the dt will be
15-(2^32-5) = 20-2^32. To get the correct number of cycles, you have to
add in 2^32, leaving you with dt = 20.
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