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Date: Wed, 10 Jan 2007 09:11:09 -0700
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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
# 1.93182Mhz/65536=18.2065Hz

*blink*

I came across some vague hand-waving references about this oscillator
having something to do with video signals, but nothing I could make
any sense out of much less use.

So much for "someone much more familiar"... :)

I'll put this math into the code and try it out again; hopefully this
will further reduce the drift that I'm seeing (and thus reduce how
often I need to requery the DOS clock).  As it is, I've already cut
20% off the performance in my program!  (It makes heavy use of
pth_nap() which uses gettimeofday() internally.)