[time-nuts] Fwd: M12+T ASCII interface - I'm confused?

Tom Van Baak tvb at LeapSecond.com
Thu Nov 20 12:44:05 EST 2008


>> You misunderstand. You can get as close to 100% as you
>> want. Some of us have logged data from M12+ receivers without
>> error for weeks or months -- gigabytes, error-free.
> 
> Sure, I assume you refer to the case when you check the data length as
> well? I meant that the <Checksum><cr><lf><@><@> byte string could also
> potentially exist in the data itself, but only in very rare cases
> (from there the 95% thumb suck).

Yes, you must use the data length. These are *packets*; all
of which have their own fixed length. See pages 30, 31 of the
M12+ user manual.

>> If you're brave you can process the message, byte by byte,
>> field by field, as it arrives in real time and use the checksum
>> as a commit.
> 
> Again, the checksum could be part of the data string - so without
> checking the data length you'll be waiting for the @@ (less probable
> to exist in data).

No no, the checksum is a designated byte at a known offset
within the packet. You first read the whole packet. Then you
validate the checksum byte and/or do other sanity checks on
the data. You don't just go looking through all the bytes in the
packet for any old byte that equals some value.

Maybe re-read Hal's message where he talked about a hunt
and sync mode. That got the point across nicely.

I hope you end up liking the binary format; I'm not sure how it
could be improved.

/tvb





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