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source= http://www.piclist.com/piclist/2004/03/26/132954a.txt?

Francisco J. A. Ares  says:
>If the final meaning of this is to set the clock on the PIC board, can't
>you simply make a program that sends the date/time information from the
>computer first?

Here's another stab at capturing the PPP packets sent from NTP.
This time, I caused Win 2000 to avoid compression.
I have added whitespace, and arbitrary material enclosed in () to aid
understanding.  I have RFC 1305 handy as well.

 From what I can see, beginning at about byte 56 of the packet is the
current time, in elapsed seconds and fractions since Jan 1, 1900 referenced
to GMT at 12:00 noon.

So a fixed-point number, containing the exact time, passes through the
serial line periodically.

 From where my system is now, I need to write a routine to recognize the
packets, to put two times in a FIFO, to subtract 64 bit numbers, to keep
the timer time up to 64 bits, and to do a subtract (to obtain PIC cycles
per second)



( 3/27/2004 11:03:35 CDT 215 [3267])
7E2145
00004C8C 1E000080 7D31B46D
CEC4512B (vima.austin.tx.us)
9206481F (ccwf.cc.utexas.edu)
007B 007B 0038E88C 7D330406
(ntp's UDP packet)
EE
000025A5 (Root Delay)
0000386B (Root Dispersion)
9206481F (Reference Clock Identifier)
C41009C3 (whole.fraction) 4C6E2A80 (Reference Epoch)
C4103229 (whole.fraction) F916F000 (Originate)
C410322A (whole.fraction) B583621F (Receive)
C4103268 (whole.fraction) 44A85CAA (Transmit)

D31E7E

( 3/27/2004 11:04:40 CDT 280 [32A8])
7E2145
00004C8C 21000080 7D31B46A
CEC4512B 9206481F
007B 007B 0038E780 7D330406
EE
000025A5
000038AA
9206481F
C41009C34C6E2A80  (Reference Epoch)
C41032690C348000
C4103269C85436B8 C41032A85AE9BBF0
0B047E

( 3/27/2004 11:05:42 CDT 342 [32E6])
7E2145
00004C8C 33000080 7D31B458
CEC4512B 9206481F
007B 007B 00384570 7D330406
EE
000025A5
000038E8
9206481F
C41009C34C6E2A80  (Reference Epoch)
C41032A921DF0000  (3DH)
C41032A9DE643CC0  (3DH)
C41032E8712A94FF
73797E

( 3/27/2004 11:06:48 CDT 408 [3328])
7E2145
00004C8C 38000080 7D31B453
CEC4512B 9206481F
007B 007B 003866B9 7D330407
EE00
00307D5D
00008209
9206481F
C41032E9F4AB3EDD (Reference Epoch)
C41032E9378BE000 (3FH)
C41032E9F4AB3EDD (3FH)
C410332987D17D33
83C26D7E

( 3/27/2004 11:08:56 CDT 536 [33A8])
7E2145
00004C8C 3E000080 7D31B44D
CEC4512B 9206481F
007B 007B 0038EE47 7D330407
EE00
00307D5D
00008286
9206481F
C41032E9F4AB3EDD (Reference Epoch)
C410332A52D9E000 (7EH)
C410332B1208BFC2 (7Dh)
C41033A9B46DA448
6C327E

( 3/27/2004 11:11:06 CDT 666 [342A])
7E2145
00004C8C 42000080 7D31B449
CEC4512B 9206481F
007B 007B 0038BBBB 7D330407
EE00
00307D5D
00008305
9206481F
C41032E9F4AB3EDD (Reference Epoch)
C41033AA78ED8000 (80H)
C41033AB359F1AE2 (7FH)
C410342AE1606317 (
59C77E


- ---
Aubrey  McIntosh
http://www.piclist.com/member/AM-vima-Y84
PIC/PICList FAQ: http://www.piclist.com


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