[aprssig] Question about 'H-bit' handling and WIDEn-N paths

[Curt, WE7U]

On Fri, 28 Jan 2005, James Washer wrote:

> I'm using an AVR along with an MX614

Yea!  Another AVR users.  Perhaps we should compare notes...  Using
GCC for your compiler?


> Ok.. you bring up another interesting question. You say that by
> keeping a history of 30seconds worth of CRC's we can avoid sending
> dupes, but setting the H-bit OR decrementing WIDEn-N/TRACEn-N will
> change the CRC. So what are they doing? Calculating a special CRC
> on the payload or something?

Whatever method you wish.  If it were me I'd think about computing a
CRC-16 on just the INFO field of the packet, and keeping it for 30
seconds.  That way any changes to the header fields wouldn't affect
the dupe-checking at all.  No user or digi would be able to
circumvent the dupe-checking.

--
Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
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