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Re: [lwip-devel] PPP single threaded

From: Alain M.
Subject: Re: [lwip-devel] PPP single threaded
Date: Thu, 11 Dec 2008 13:43:17 -0200
User-agent: Thunderbird (X11/20080914)

Hi Simon,

I am new to lwip but I hope that I can help. I have been working with PSilva, I did most of the protocol decoding to find the problem...
I've put some work into getting PPP working in a single-threaded (NO_SYS = 1) environment.
My first suggestion is that you make it over a Linux port, it really helps A LOT to debug. Peter's test is running, but with threads, it should be relatively easy to remove the threads. Al least it will make it easyer FOR ME to help :)
I've also put some time into refactoring the existing PPP code to match more with the rest of lwIP, mostly renaming though. I've also implemented a really simple 'chat' module, to setup a GPRS connection. Now I wonder if the effort should be made to bring this all back into lwIP. There is still a lot to do, but it would probably be worth it.
Please, do ...
Let me explain what I changed in the design:
* Added a simple timesys module to PPP, this is ticked by a call to ppp_tmr() like the rest of lwIP. This timesys implements a jiffies counter which PPP needs in some places.
is jiffies used only in PPP? Usualy you will get it from the RTOS, so I would suggest that a more generic function be used.
It also implements the timeout handlers, which are absent in lwIP for the NO_SYS = 1 case, but still necessary in PPP. I think this puts PPP more in line with the rest of the lwIP core. * Added ppp_poll(pd) function, which needs to be called periodically when in single-threaded mode.
Yes, ans yes...
This all seems to work fine so far. I wonder though, how to make this working again in a multi-threaded environment, where we have a separate thread to poll the serial for input.
what usualy works just fine is to put all your code into a single thread. Simple, easy and portable. Once the connection is established, the thread could just close.
I guess the PPP input and output paths are not thread-safe, so they would have to be synchronized in some way.
I am not familiar with lwip , but from my experience with other systems, I can say this: PPP has parts: 1) making the connection, in this part noone should use the serial port and the ppp can use sio_xxx without wory 2) once the connection is established, it is a "packet driver" just like the ethernet one. And I believe that lwip already must have solved that problem ;)
The current approach with calling tcpip_callback() all the time does not look like the right way to me.
agreed, but only theoreticaly because of lack of knowledge of lwip.
Is anyone interested on collaborating on this?
I can help some... specially on a Linux port. Real hardware is with PSilva, but I indend to get another one soon.

I have sent to the list a sio_read() that can be aborted, I can easely conver it to a nonblocking timeouted one.
I've heard from quite a few guys now, who did their own hacks to get PPP working in a single-threaded environment, and I think it's time to get it right. Any input is welcome!
I hope that I can help, at least with chearing :)


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