RE: [lwip-users] Slow response times in Microblaze Webserver example

[Pisano, Edward A]

Hi John,
I had seen similar slow response with the WebServer example.  It turned
out to be the debug output messages.  The RS-232 output has a
significant slowing effect on lwIP.  In my case, ping replies were
taking 1700ms to 3400ms on  the Spartan 3E.  I turned off LWIP_DEBUG and
commented out my own xil_print() statements.  Ping replies quickly
dropped to 17ms-25ms.

Regards,
Ed
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Sent: Tuesday, September 19, 2006 5:47 AM
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Subject: [lwip-users] Slow response times in Microblaze Webserver
example

Dear All,

I have been testing a program modified from the Webserver example for
the 
Xilinx Spartan3e Starter Kit. A client application on a PC connected to
the 
board via a crossover cable issues a GET command, to which the server
should 
respond with a short string, about 50 bytes. 

The problem that I am finding is that, although the response is
occasionally 
very fast, 99% of the time the response may take several seconds. Since
my 
eventual application is a fairly fast data acquisition requirement, this
is a 
problem.

To debug this, I first removed the mfs part of the Webserver example,
then 
added GPIO calls to the LEDs before and after the read function in 
processConnection. Using an Ant8 logic analyser, I found that the time
needed 
in this function was very occasionally 30 - 40 millisecs but almost
always 
around 2900 millisecs.

Using gdb, I traced the delay to the call in netconn_recv() to
sys_mbox_fetch() 
which blocks for 3 seconds, then all the rest of code executes as
expected. The 
fast response seems only to occur the first time both the client and
server are 
run.

In XPS I selected the debug output option, set the rs232 speed to 115kbs
and 
directed the output to a file. 

During the block period the system appears to emit at least 
six  "tcp_slowtmr:procssing active pcb messages" interspersed with some
timeout 
messages.

In case I was doing something wrong in the client code, I used the same
program 
to talk to a Netburner card, issuing the same response to a GET request.
The 
delays were of the order of a few millisecs.

So I am sure I am doing something stupid in the server code and would
really 
appreciate any help.

JOhn Robbins.






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