Re: [ECOS] CRC check on serial comm to redboot

["kjell at techtribe dot se" <kjell at techtribe dot se>]

Hi,

Yep, the remote-gdb protocol used when downloading an app over the 
serial line via gdb does also hava a checksum. However, its not a CRC 
but a pretty simple modulo-256 checksum, which could occasionally let an 
erroneous packet slip through :-(
Also remember that Redboot is polled, so at high comm speed (e.g 115200 
bps) there is not only the increased risk of getting disturbances on the 
wire, but also a higher risk that bytes might be lost due to polling 
delays on loaded targets.
So there is definitely a theoretical risk of both getting bad data and 
then having it slip through the checksum, but I haven't seen much 
problems with this in practice.

Cheers, /Kjell
--
Kjell Svensson                 Embedded Technology Manager
Techtribe Solutions AB         Tel:  +46 (0)31 706 06 00
Flöjelbergsgatan 12            GSM:  +46 (0)70 270 76 66
SE-431 37  MÖLNDAL             Mail: kjell@techtribe.se
Sweden




Andrew Lunn wrote:
> On Wed, Feb 05, 2003 at 05:42:52AM +0100, Magnus Ekhall wrote:
>
> > > Im confused here. You say serial port, but was asking about TFTP
> > > checksums?
> > I'm probably the one confused: I actually meant if the serial line
> > communication is error checked somehow?
>
> I think XYZ modem has a 16bit CRC. gdb does have a CRC for its
> protocol.
>
>         Andrew


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