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lwIP port status
- From: Simon Kallweit <simon dot kallweit at intefo dot ch>
- To: "ecos-devel at ecos dot sourceware dot org" <ecos-devel at ecos dot sourceware dot org>
- Date: Mon, 18 May 2009 16:41:58 +0200
- Subject: lwIP port status
It's time for a little status update on the lwIP 1.3.x port. Let me give
you a little list of what has been done lately:
* CDL should include every configuration option offered by lwIP now, was
reviewed by John Dallaway and got restructured and cleaned up afterwards.
* Implemented 'Sequential' mode.
* Updated to the latest lwIP sources from CVS again.
* Reviewed test cases.
* Cleanup, cleanup, cleanup.
What's left to do is lots of testing and writing documentation etc. I
think it would be great to finish the port when lwIP hits the 1.3.1
release which should not be too far from now. If time permits, I may
also work a bit on PPP.
For now I would like to shortly discuss my 'Sequential' implementation.
In 'Sequential' mode, lwIP is configured with NO_SYS == 0 and allows for
multiple threads to use the stack (netcomm, sockets). The main thread
(tcpip) is basically used to synchronize all threads accessing the stack
by sequentially processing incoming messages on a message queue. When a
packet arrives on an interface, a message pointing to the packet is sent
to the message queue. This is what is done with the SLIP interface for
example. SLIP is running in it's own thread, reading from the serial
device (blocked). When a packet is received, it is passed to the tcpip
thread by posting a message to the message queue. This way the packet is
processed in sync with the tcpip thread. For ethernet devices I choose
another path. The old port implemented a separate ethernet delivery
thread which would wait on a semaphore for packets to arrive. It would
wake up when a packet arrives and read it from the interface and send a
message to the tcpip thread. In my port I got rid of the delivery thread
and implemented sending/receiving as follows:
When a packet is sent, lwIP assumes that after the call to output the
packet, the packet is no longer access by the driver and can be
released. This means that the packet should be sent before the call
returns -> blocking, or packets would have to be copied and put in a
queue, which I think does not make much sense. I therefore implemented
sending to be blocking.
Receiving packets could be done in parallel to the tcpip thread, but
packets still have to be processed in sync to the tcpip thread. I choose
a really simple route. When a packet arrives, a callback is registered
with the tcpip thread, which is called back as soon as ongoing
processing in the tcpip thread is finished. The callback then reads all
the pending packets from the ethernet devices and directly processes them.
What do people think of this approach? Is it feasible or completely
Anybody cares to do some testing of the new lwIP port?