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Re: [lwip-users] Driver interface related question

From: Frédéric BERNON
Subject: Re: [lwip-users] Driver interface related question
Date: Wed, 17 Oct 2007 23:24:41 +0200

----- Original Message -----
Sent: Wednesday, October 17, 2007 11:43 AM
Subject: [lwip-users] Driver interface related question


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?




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