[aprssig] which digi
Kai Gunter Brandt
kai.brandt at hjemme.no
Thu Feb 26 15:30:46 CST 2009
Scott Miller skrev:
>> If the digipeater callsign are LD5BE you can connect to this changing
>> your UNPROTO to LD5BE
> So it's just an UNPROTO packet and not an APRS message?
>> Send a "empty" packet and the TNC responds with a string.
>> Put this string into a calculator and send the result back.
>> If password is ok then you can change everything but the callsign.
> So it's a challenge-response authentication scheme of some sort. Are
> the details of the scheme public?
Yes you store a password in the TNC the first time. Based on this you
get a string and you have to calculate this. Not a very advanced method
but it's probably enough security. It's a java applet.
>> Upgrading firmware over the air sounds spooky ;o) is there a fallback if
>> it fails?
> For the SR1, the firmware is sent in numbered blocks, one packet at a
> time. As each block is received (and the packet checksum passes) it
> gets written to the appropriate place in temporary (in this case,
> external flash) memory. Once every block has been sent, a 'write'
> command provides the start/end address and a master checksum. If the
> checksum for the received firmware passes, it stops what it's doing,
> jumps to the bootloader, and writes everything to internal flash and resets.
> You can take as long as you want to send all of the blocks, and it'll
> just set aside that 64k block of flash and not use it for anything else
> while it's keeping firmware there.
ahh interesting and probably very stable. without a system like this it
would probably be more safe going to to do the upgrade manualy.
> For a proper on-air format, there should be a way for the sending
> station to request a list of missing blocks. So you'd sent each block
> once, expecting no acknowledgment, and then see which ones were missed.
> You'd send all of the missing blocks and then query again, until all
> were received and the checksums matched.
use torrent ;o)
The old checksum system used in computer magazines could probably be
used but i'm not sure how complicated this is. I remember that this
system could tell me that there was an error in line xx position yy.
But i see what you want and this seems like a better and faster method
flashing over RF without all the ACK etc.
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