I learned about the CRC escaping for sure by experience, like every once in a while I would get a packet with the CRC escaped, which caused occasional errors if I didn't unescape it. Logically, you would have to escape anything between the framing bytes or else it would have the potential to mess up the framing logic, but you never know how logically the actual code has been implemented.
Ben -----Original Message----- From: Michael Schippling [mailto:[EMAIL PROTECTED] Sent: Monday, April 09, 2007 10:16 PM To: Ben Buckner Cc: [email protected] Subject: Re: [Tinyos-help] CRC checking Sounds right... however... I've not seen an exposition of what happens when the CRC has a 7{e,d}... Logically your algorithm works, but in practice we'd have to reverse engineer the TOS code... The CRC is part of the T_M packet since data[] is encapsulated, and it's at the end so some(unspecified)one _could_ do a fully serial packet generation, the execution of which I have never seen. MS Ben Buckner wrote: > The way my code calculates it is to concatenate the packet type byte and the > payload (TOS_Msg). Then I CRC that all together, append the CRC (low byte > first), and run the escaper on it all (don't forget to catch both 7Es and > 7Ds). Then I prepend and append the 7E synch bytes. Seems to work. I'm not > sure why the CRC is part of TOS_Msg, since it seems like it functionally > belongs to the raw packet layer, but that's the way it is I guess. The > Octavetech doc notes this peculiarity as well. > > To test, you can try to CRC the example packet in the Octavetech doc and see > if you get the same result. > > Regards, > Ben Buckner > > -----Original Message----- > >> I thing that's in the octavetech page, but I believe it is all bytes >> including header, before escapes are applied. >> I'm not sure but I think the pre-amble 7E 4x is not included. >> >> MS >> >> jurin dan wrote: >>> thanks a lot for your reply. >>> >>> just one more thing. within the raw data packet, which byte do i use to >>> compute the CRC. >>> is it all byte or only TOS_MSG byte. > > > > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help _______________________________________________ Tinyos-help mailing list [email protected] https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
