[lwip-users] PPPoS: ppp session disconnect if hit bad fcs for LCP packet

[Axel Lin]

Hi,
I hit a strange issue regarding PPP disconnect.

I use below setting to enable sending LCP echo request:
#define LCP_ECHOINTERVAL               2
#define LCP_MAXECHOFAILS               20

I found if I hit bad fcs case for LCP packet in pppos_input(), the PPP
session closed soon.
This seems does not make sense because in my configuration it needs to
at least 20 failures
to trigger LcpLinkFailure() to close the PPP session. But I just hit 1 bad fcs.
I know the PPP session closed becasue I got PPPERR_PEERDEAD in link_status_cb.

bad fcs case:
ppp->netif->num = 0
pppos->in_fcs = 0xeae4
pppos->in_protocol = 0xc021 (LCP)

It's not easy to hit this issue, usually it needs to run for a couple
hours or more than one day.
But the symptom seems to be the same.

BTW, my device always keep sending data to LTE through pppos.
I'm wondering why the bad fcs usually happened on LCP packet.

I'm still debugging this issue, I appreciate for any comments.

Thanks,
Axel