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From:	"Rod Pemberton" <do_not_have AT bitfoad DOT cmm>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Performance enhancement for gettimeofday()?
Date:	Wed, 10 Jan 2007 13:25:42 -0500
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<Gordon DOT Schumacher AT seagate DOT com> wrote in message
news:OF77475379 DOT 7BA371D5-ON8725725F DOT 00598107-8725725F DOT 0059B5ED AT seagate DOT com...
> Rod Pemberton wrote on Tue, 9 Jan 2007 at 03:46:03 -0500:
>
> # I believe this it the math you'll need:
> #
> # 14.318Mhz=4*3.58Mhz=4*(4.5Mhz*455/572)
> #     (4.5Mhz US TV bandwith/channel, 455 colorburst phase changes/line,
> 572
> # total lines/frame including sync)
> # 14.318Mhz/12=1.93182Mhz
>
> Aha, this is the one that's why our numbers don't agree:
> 14.318MHz divided by 12 is actually 1.193666... MHz.
>

Sorry, it appears I failed to type a 1 following the decimal.  It's not
14.318000MHz, but 14.318181MHz.  You really need to enter
4*4.5*(10^6)*455/572 to compute the 14.318MHz and work from there.  IIRC
('twas 25+ years ago), it's 4 times the colorburst as calculated by the
original engineer who designed the US color TV standard.  That way you won't
loose precision.  Of course, a real crystal usually has a tolerance range,
but that range is usually small compared to the frequency, like +/- 100Hz or
+/-10KHz.  Of course, you could go to Mouser or another electronic supplier,
and look for a crystal if you think the range would help.

Like you, I'll use ... for repeating digits.  The 1 and 8 repeat for both.
I was using more decimals but rounded/truncated.

14.318181818181...  Mhz  / 12 = 1.193181818181... Mhz.
1.193181818181...Mhz / 65536 = 18.206509676846 Hz


Rod Pemberton

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