Hi All,
I use the last CVS Head LWIP on LPC2468 with FreeRTOS. My embedded system
communicates by IP with a PC. When the PC IP interfaces restart, I look for a
checksum incorrect packet on Wireshark.
This error seems to be a concatenate error. 172.17.2.173:my embedded system
with LWIP; 172.17.2.172 : PC
111 7.819682 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=55493 Ack=0 Win=5840 Len=209
112 7.825543 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [ACK] Seq=0 Ack=55702 Win=65535 Len=0
113 7.993714 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=55702 Ack=0 Win=5840 Len=531
114 7.997536 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [ACK] Seq=0 Ack=56233 Win=65535 Len=0
115 8.211446 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [ACK] Seq=56233 Ack=0 Win=5840 Len=1460
116 8.301504 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [ACK] Seq=0 Ack=57693 Win=65535 Len=0
117 8.326219 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=57693 Ack=0 Win=5840 Len=197
118 8.333736 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [ACK] Seq=0 Ack=57890 Win=65535 Len=0
119 8.422016 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=57890 Ack=0 Win=5840 Len=1126
120 8.429543 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [ACK] Seq=0 Ack=59016 Win=65535 Len=0
121 8.632683 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=59016 Ack=0 Win=5840 Len=934
122 8.634010 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [ACK] Seq=0 Ack=59950 Win=65535 Len=0
123 8.869443 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [ACK] Seq=59950 Ack=0 Win=5840 Len=1460 <- Restart of the PC IP
interfaces
125 8.871878 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [ACK] Seq=61410 Ack=0 Win=5840 Len=1460
129 8.874047 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [ACK] Seq=0 Ack=62870 Win=65535 Len=0
130 9.307578 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=62870 Ack=0 Win=5840 [TCP CHECKSUM INCORRECT] Len=740
<- this packet is a concatenation of the same packets than 111 and 113
131 9.309162 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [ACK] Seq=63610 Ack=0 Win=5840 Len=1460
132 9.309293 172.17.2.172 172.17.2.173 TCP [TCP
Dup ACK 129#1] 48955 > 5678 [ACK] Seq=0 Ack=62870 Win=65535 Len=0
142 9.789090 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=65070 Ack=0 Win=5840 [TCP CHECKSUM INCORRECT] Len=1323
<- this packet is a concatenation of the same packets than 117 and 119ss
153 10.003902 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [PSH, ACK] Seq=66393 Ack=0 Win=5840 Len=934
156 10.019539 172.17.2.172 172.17.2.173 TCP [TCP
Dup ACK 129#2] 48955 > 5678 [ACK] Seq=0 Ack=62870 Win=65535 Len=0
157 10.905015 172.17.2.173 172.17.2.172 TCP [TCP
Retransmission] 5678 > 48955 [PSH, ACK] Seq=62870 Ack=0 Win=5840 [TCP CHECKSUM
INCORRECT] Len=740
158 13.209979 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [PSH, ACK] Seq=0 Ack=62870 Win=65535 Len=1
159 13.210040 172.17.2.172 172.17.2.173 TCP 48955
> 5678 [FIN, ACK] Seq=1 Ack=62870 Win=65535 Len=0
160 13.210332 172.17.2.172 172.17.2.173 TCP 48956
> 5678 [SYN] Seq=0 Len=0 MSS=1460 TSV=1711037 TSER=0 WS=6
161 13.241498 172.17.2.173 172.17.2.172 TCP 5678 >
48955 [ACK] Seq=67327 Ack=2 Win=5838 Len=0
162 13.279770 172.17.2.173 172.17.2.172 TCP 5678 >
48956 [SYN, ACK] Seq=0 Ack=1 Win=5840 Len=0 MSS=1460
163 13.279930 172.17.2.172 172.17.2.173 TCP 48956
> 5678 [ACK] Seq=1 Ack=1 Win=5840 Len=0
164 14.205872 172.17.2.173 172.17.2.172 TCP [TCP
Retransmission] 5678 > 48955 [PSH, ACK] Seq=62870 Ack=2 Win=5838 [TCP CHECKSUM
INCORRECT] Len=740
In the pbuf_cat function "p->next" must not be equal to "t", but must be equal
to "NULL". And we must write "p->len+=t->len;". And next after the call of
"pbuf_cat(useg->p, queue->p);" in "tcp_enqueue fuction" tcp_out.c , we have
Add two line:
pbuf_cat(useg->p, queue->p);
useg->len += queue->len;
useg->next = queue->next;
LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
("tcp_enqueue: chaining segments, new len %"U16_F"\n", useg->len));
if (seg == queue)
{
seg = useg;
seglen = useg->len;
queuelen--; //decrementation of the SND_QUEUELEN due to
concatenation
}
memp_free(MEMP_TCP_SEG, queue);
pbuf_free(queue->p); /dereference a pbuf chain due to concatenation
Thanks to this modification I haven't a TCP CHECKSUM INCORRECT in wireshark and
the communication works fine.
Can you tell me if this modification are the best and if they will not be
cause of a problem.
Thanks In advance,
Hervé GARAT
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