Re: [lwip-devel] PPP single threaded

[Alain M.]

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 :)

Alain