Re: [lwip-users] Re transmission problem?

[Jordan Dean]

I have seen the exact thing using the Xilinx lwip examples.  There are a few
things (I have since found out) that are wrong about the way they have the
examples set up.  The first thing to do is to fix the way they call the
timers.

Xilinx sets up the microblaze timer and uses the interrupt to call tcp_fast
and slow timers, this is incorrect.  What you need to do to fix the weird
ack problems is to use the Xilinx timer interrupt to set a global flag
do_tcp_fast  and do_tcp_slow.  Check those global flags in your main program
loop and use them to call the timers (not from the interrupt context).  This
fixed these types of issues for me.


Then what you need to do is port the Xilinx driver to 1.4, it works much
smoother.

-Jordan 

Sent: Friday, May 13, 2011 3:56 AM
To: address@hidden
Subject: [lwip-users] Re transmission problem?


Hi,

I am currently running LwIP 1.3.0 v3.01a on a Xilinx dev board connected to
a host PC and using the RAW API.  To measure the maximum bandwidth I
repeatedly transmit blocks of 1400 bytes from the board to the PC using the
module at the end of this email called in a while loop from main.c.

I achieve a bandwidth of 100Mb/s however between 5-10mins transmission
stops.  Looking at the Wireshark capture below there is a retransmission at
462735 of the previously sent frame (462733) followed by a duplicate ACK,
the next frame sent is the frame which would be expected if the
retransmission did not occur.  From this point on there are several
duplicate ACKs but the frames between the ACKs are not retransmitted frames.

Does this indicate a problem with LwIP retransmission? As after the
retransmission I would have expected the next frame in the seqeuence not the
frame after that which the retransmission replaced.

Also I have noticed that occasionally there are 3 frames between ACKs,
should it not always be 2 for every ACK at this data rate?

Thanks for your help,
Phil

Wireshark capture:

462720 41.694753   192.168.1.10          192.168.1.2           ECHO     1454

Response
 462721 41.694901   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462722 41.694914   192.168.1.2           192.168.1.10          TCP      54

57774 > echo [ACK] Seq=4242681 Ack=430759001 Win=65535 Len=0
 462723 41.694953   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462724 41.695106   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462725 41.695121   192.168.1.2           192.168.1.10          TCP      54

57774 > echo [ACK] Seq=4242681 Ack=430761801 Win=65535 Len=0
 462726 41.695155   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462727 41.695314   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462728 41.695334   192.168.1.2           192.168.1.10          TCP      54

57774 > echo [ACK] Seq=4242681 Ack=430764601 Win=65535 Len=0
 462729 41.695370   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462730 41.695516   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462731 41.695531   192.168.1.2           192.168.1.10          TCP      54

57774 > echo [ACK] Seq=4242681 Ack=430767401 Win=65535 Len=0
 462732 41.695571   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462733 41.695733   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462734 41.695750   192.168.1.2           192.168.1.10          TCP      54

57774 > echo [ACK] Seq=4242681 Ack=430770201 Win=65535 Len=0
 462735 41.695789   192.168.1.10          192.168.1.2           ECHO    
1454   [TCP Retransmission] Response
 462736 41.695800   192.168.1.2           192.168.1.10          TCP      54

[TCP Dup ACK 462734#1] 57774 > echo [ACK] Seq=4242681 Ack=430770201
Win=65535 Len=0
 462737 41.695924   192.168.1.10          192.168.1.2           ECHO    
1454   [TCP Previous segment lost] Response
 462738 41.695940   192.168.1.2           192.168.1.10          TCP      54

[TCP Dup ACK 462734#2] 57774 > echo [ACK] Seq=4242681 Ack=430770201
Win=65535 Len=0
 462739 41.696079   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462740 41.696101   192.168.1.2           192.168.1.10          TCP      54

[TCP Dup ACK 462734#3] 57774 > echo [ACK] Seq=4242681 Ack=430770201
Win=65535 Len=0
 462741 41.696203   192.168.1.10          192.168.1.2           ECHO    
1454   Response
 462742 41.696219   192.168.1.2           192.168.1.10          TCP      54

[TCP Dup ACK 462734#4] 57774 > echo [ACK] Seq=4242681 Ack=430770201
Win=65535 Len=0
 462743 41.696253   192.168.1.10          192.168.1.2           ECHO    
1454   [TCP Out-Of-Order] Response
 462744 41.696261   192.168.1.2           192.168.1.10          TCP      54

[TCP Dup ACK 462734#5] 57774 > echo [ACK] Seq=4242681 Ack=430770201
Win=65535 Len=0
 462745 41.703125   192.168.1.2           192.168.1.10          ECHO    
1514   Request
 462746 41.703131   192.168.1.2           192.168.1.10          ECHO     594

Request
 462747 41.734051   192.168.1.2           192.168.1.10          ECHO    
1514   Request
 462748 41.734056   192.168.1.2           192.168.1.10          ECHO     594

Request
 462749 41.749768   192.168.1.2           192.168.1.10          ECHO    
1514   Request
 462750 41.749776   192.168.1.2           192.168.1.10          ECHO     594

Request
 462751 41.765325   192.168.1.2           192.168.1.10          ECHO    
1514   Request
 462752 41.765331   192.168.1.2           192.168.1.10          ECHO     594

Request
 462753 41.983547   192.168.1.2           192.168.1.10          ECHO    
1514   [TCP Retransmission] Request
 462754 42.591959   192.168.1.2           192.168.1.10          ECHO    
1514   [TCP Retransmission] Request
 462755 43.675781   192.168.1.10          192.168.1.2           TCP      60

echo > 57774 [ACK] Seq=430771601 Ack=4250681 Win=8192 Len=0
 462756 43.675840   192.168.1.2           192.168.1.10          ECHO    
1514   Request

Transfer data module:

int
transfer_echo_data()
{
  err_t err;
  struct tcp_pcb *tpcb = connected_pcb;

  if (!connected_pcb) {
    xil_printf("Not connected\r\n");
    return ERR_OK;
  }

  if (tcp_sndbuf(tpcb) > SEND_BUFSIZE) {
    err = tcp_write(tpcb, send_buf, SEND_BUFSIZE, 0);
    if (err != ERR_OK) {
      xil_printf("Error on tcp_write: %d\r\n", err);
      connected_pcb = NULL;
      return -1;
    }
    tcp_output(tpcb);
  }

  send_buf[1]++;
  
  return 0;
}


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