[lwip-users] RE: Re: Driver interface related question

[KATZIR SHAY]

Hello,

I'm using the 1.2.0 version of lwip without cvs changes.
I ported the package by creating the sys_arch functions as requested, but 
didn't use the SYS_LIGHTWEIGHT_PROT.  

As i wrote in my previous e-mail, i have a multithread system and i use 
interrupt for receiveing packets. I read in previous disscussions (bug in PBUF) 
that it is unsafe to use the pbuf from the interrupt, but i have no choice and 
i'm trying to get it to work.
after failing to manage without SYS_LIGHTWEIGHT_PROT (the program got stuck 
quickly) i wrote the sys_protect funcs, and changed the macro to one but it got 
worse, and kept giving debug messages of "out of memory" on memp "TCP_MSG" and 
pbufs.

can anyone explain me which method should i use for using this package in a 
multithreaded system? and how can i use the receiving interrupt to enter a 
packet to the tcpip mailbox, without blocking the interrupt.

thanks,
shai 


Subject: Re: [lwip-users] Driver interface related question
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Driver interface related question----- Original Message ----- 
  From: KATZIR SHAY 
  To: address@hidden 
  Sent: Wednesday, October 17, 2007 11:43 AM
  Subject: [lwip-users] Driver interface related question


  Hi,

  In order to write an interface for my ethernet driver,
  I used the ethernetif.c and etharp.c, given in the lwip package.

  1. because my driver api function for Send, writes the data immediately to 
the register, I had to send the Packet in one buffer, and not each pbuf in the 
chain separately. Therefore, I created in low_level_output a new pbuf which 
collects the pbufs in the chain into single pbuf chain, and then send to the 
driver the new pbuf, and release him by pbuf_free.

  Can it cause any problem? Can it encounter a separate call for pbuf_free()?

No, I don't think

  2. After managing to create the driver interface, and to port the lwip into 
my system by writing sys_arch of my own. It can now communicate with other 
computers, but
     after running for few seconds, it get stuck in an endless loop, usually in 
the mbox_fetch of the tcpip_thread, even though the driver keeps on getting 
packets.

     I made a lot of tests, and in each test it got stuck in a different phase 
of the program.

Most of time, it's a port problem. What lwIP release do you use?

     I believe it enters some sort of race condition.
    My main worry is about the interrupt of the driver which handles the 
receive.
    This Interrupt calls the callback function - 'ethernetif' and pass the data 
to him. When the Packet enters the function, it gets processed as an IP Packet 
or an ARP Packet. In both cases, the function uses semaphores (memp sem and 
pbuf_pool_free sem), which can easily create a block to the program (because 
those sems are occupied by the application or the tcpip thread) .
  Is there a way of handling the input packet without using any semaphores? 
What is the common implementation for the input callback of the driver?

Take a look to 
http://lists.nongnu.org/archive/html/lwip-users/2007-09/msg00097.html, there is 
some informations from Jonathan about a Zero Copy Ethernet interface. Perhaps 
it can give you some ideas? 

  Can you see any other solution for my problem?

  Thanks,

  Shai.

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