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Re: [lwip-users] Case Of The Missing ACK


From: davidm
Subject: Re: [lwip-users] Case Of The Missing ACK
Date: Tue, 08 Sep 2009 08:45:36 +1000
User-agent: Thunderbird 2.0.0.23 (Windows/20090812)

Kieran Mansley wrote:
On Mon, 2009-09-07 at 14:58 +1000, address@hidden wrote:
Perhaps others have encountered this and would offer comments and perhaps comments could be offered in general.

That is weird.  It's hard to tell which end is lwIP and which is WinXP
in your packet capture, but at the point at which things go wrong I
notice the direction of the traffic changes.  Until then, 192.168.2.2 is
sending to 192.168.2.3, at that point ...2.3 starts sending to ...2.2

Is there anything in the lwIP stats that might explain why packets are
dropped?  Could it be that your board just gets very busy (perhaps with
something like debug output?) and takes a very long time to respond?

Kieran



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I should have explained - 192.168.2.2 is lwIP. At line 32 of Wireshark, a concatenated number of requests are sent which the MCU responds individually, echoing the request prior to sending the response data. This explains the multiple packets from lwIP to the client (192.168.2.3).

At line 103 the request to enter binary mode is sent with the request echoed at line 105 and the acceptance response at line 106.

I have attached a file which shows the stats just prior to entering binary mode and just after returning to text mode. All seems to be ok there.

There should be no delay due to the MCU being busy (other than task switching) as all that is done is to partially load and internal buffer which once filled, is written to an SD card Flash sector.

A question: When the debug output "tcp_recved: recveived 46 bytes, wnd 2048 (0)" is delivered, should an ACK already have been sent by lwIP, or does that occur later?

At a later time I should put a debug breakpoint on the receipt of the 46 byte packet and trace through the internals of lwIP.

And by the way, thank you for your input. If nothing else I'm honing my skills in the finer art of lwIP debugging.

Regards - davidm

.
Before              After
-----------         ------------

LINK                            LINK       
xmit: 117                       xmit: 133  
rexmit: 0                       rexmit: 0  
recv: 81                        recv: 96   
fw: 0                           fw: 0      
drop: 0                         drop: 0    
chkerr: 0                       chkerr: 0  
lenerr: 0                       lenerr: 0  
memerr: 0                       memerr: 0  
rterr: 0                        rterr: 0   
proterr: 0                      proterr: 0 
opterr: 0                       opterr: 0  
err: 0                          err: 0     
cachehit: 0                     cachehit: 0
                                  
ETHARP                          ETHARP                      
xmit: 3                         xmit: 3                     
rexmit: 0                       rexmit: 0                   
recv: 10                        recv: 10                    
fw: 0                           fw: 0                       
drop: 0                         drop: 0                     
chkerr: 0                       chkerr: 0                   
lenerr: 0                       lenerr: 0                   
memerr: 0                       memerr: 0                   
rterr: 0                        rterr: 0                    
proterr: 0                      proterr: 0                  
opterr: 0                       opterr: 0                   
err: 0                          err: 0                      
cachehit: 109           cachehit: 125               
                                                                
IP                                  IP                          
xmit: 112                       xmit: 128                   
rexmit: 0                       rexmit: 0                   
recv: 71                        recv: 86                    
fw: 0                           fw: 0                       
drop: 0                         drop: 0                     
chkerr: 0                       chkerr: 0                   
lenerr: 0                       lenerr: 0                   
memerr: 0                       memerr: 0                   
rterr: 0                        rterr: 0                    
proterr: 0                      proterr: 0                  
opterr: 0                       opterr: 0                   
err: 0                          err: 0                      
cachehit: 0                     cachehit: 0                 
                                                                
ICMP                            ICMP                        
xmit: 0                         xmit: 0                     
rexmit: 0                       rexmit: 0                   
recv: 0                         recv: 0                     
fw: 0                           fw: 0                       
drop: 0                         drop: 0                     
chkerr: 0                       chkerr: 0                   
lenerr: 0                       lenerr: 0                   
memerr: 0                       memerr: 0                   
rterr: 0                        rterr: 0                    
proterr: 0                      proterr: 0                  
opterr: 0                       opterr: 0                   
err: 0                          err: 0                      
cachehit: 0                     cachehit: 0                 
                                                                
UDP                                 UDP                         
xmit: 2                         xmit: 2                     
rexmit: 0                       rexmit: 0                   
recv: 2                         recv: 2                     
fw: 0                           fw: 0                       
drop: 0                         drop: 0                     
chkerr: 0                       chkerr: 0                   
lenerr: 0                       lenerr: 0                   
memerr: 0                       memerr: 0                   
rterr: 0                        rterr: 0                    
proterr: 0                      proterr: 0                  
opterr: 0                       opterr: 0                   
err: 0                          err: 0                      
cachehit: 0                     cachehit: 0                 
                                                                
TCP                                 TCP                         
xmit: 95                        xmit: 105                   
rexmit: 0                       rexmit: 0                   
recv: 69                        recv: 84                    
fw: 0                           fw: 0                       
drop: 0                         drop: 0                     
chkerr: 0                       chkerr: 0                   
lenerr: 0                       lenerr: 0                   
memerr: 0                       memerr: 0                   
rterr: 0                        rterr: 0                    
proterr: 0                      proterr: 0                  
opterr: 0                       opterr: 0                   
err: 0                          err: 0                      
cachehit: 0                     cachehit: 0                 
                                                                
MEM HEAP                        MEM HEAP                    
avail: 4096                     avail: 4096                 
used: 548                       used: 548                   
max: 1568                       max: 1568                   
err: 0                          err: 0                      
                                                                
MEM RAW_PCB                     MEM RAW_PCB                 
avail: 4                        avail: 4                    
used: 0                         used: 0                     
max: 0                          max: 0                      
err: 0                          err: 0                      
                                                                
MEM UDP_PCB                     MEM UDP_PCB                 
avail: 4                        avail: 4                    
used: 1                         used: 1                     
max: 1                          max: 1                      
err: 0                          err: 0                      
                                                                
MEM TCP_PCB                     MEM TCP_PCB                 
avail: 5                        avail: 5                    
used: 1                         used: 1                     
max: 1                          max: 1                      
err: 0                          err: 0                      
                                                                
MEM TCP_PCB_LISTEN      MEM TCP_PCB_LISTEN          
avail: 8                        avail: 8                    
used: 1                         used: 1                     
max: 1                          max: 1                      
err: 0                          err: 0                      
                                                                
MEM TCP_SEG                     MEM TCP_SEG                 
avail: 32                       avail: 32                   
used: 1                         used: 1                     
max: 9                          max: 9                      
err: 0                          err: 0                      
                                                                
MEM ARP_QUEUE           MEM ARP_QUEUE               
avail: 30                       avail: 30                   
used: 0                         used: 0                     
max: 0                          max: 0                      
err: 0                          err: 0                      
                                                                
MEM PBUF_REF/ROM        MEM PBUF_REF/ROM            
avail: 16                       avail: 16                   
used: 0                         used: 0                     
max: 0                          max: 0                      
err: 0                          err: 0                      
                                                
MEM PBUF_POOL           MEM PBUF_POOL               
avail: 32                       avail: 32                   
used: 0                         used: 0                     
max: 2                          max: 2                      
err: 0              err: 0                      


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