On 01/12/11 13:40, Slawomir Skret wrote: > I added an instrumental printk statement in the ppp_receive_frame to > print a message before the ppp_receive_error(), rebuilt the kernel, and > got these prints for every error count reported. What does that mean? Is > there anything I can do/turn on/instrument/etc to tell what's wrong with > these frames? It means that your hardware is destroying the data in flight. There's not much that PPP can do about that except detect the errors (using the Frame Check Sequence -- a CRC-16 scheme) and discard the packets that are affected. You could use the "record filename" option to capture the actual raw data. That interposes a pty pair, so it's not completely transparent. To do transparent analysis, you'll need an external serial analyzer. Several vendors (such as HP) make such machines. They're by no means cheap, but if you're doing real hardware development, there's no substitute for having good test gear. Reasonable operation of PPP assumes a lower layer that has only a modest -- and hopefully not traffic-sensitive -- error rate. It doesn't have to be completely error free, but even a small error rate will have a relatively large effect on usability and performance of the link. (And systematic errors, such as [say] always discarding the 256th byte of packets with 256 or more bytes, will make the link effectively useless for ordinary networking purposes.) (This isn't really a characteristic of PPP itself, but rather of any interface intended for datagram networking purposes. Error rates other than "a little" are bad news.) > Also, I built the pppstats and run it: > > /var # ./pppstats > IN PACK VJCOMP VJUNC VJERR | OUT PACK VJCOMP VJUNC > NON-VJ > 2351664 1587 0 0 0 | 78364 1465 0 0 1465 > > but it does not report these errors. That indicates that there's no significant errors above the framing level. That's good, as it likely means there are no difficult software problems to solve. It's merely a matter of inadequate hardware. -- James Carlson 42.703N 71.076W <carlsonj@xxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-ppp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
