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

[jcr_alr]

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.