[lwip-devel] PPP single threaded

[Simon Kallweit]

Hi there

I've put some work into getting PPP working in a single-threaded (NO_SYS 
= 1) environment. 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. 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. 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.

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. I guess the PPP input and output 
paths are not thread-safe, so they would have to be synchronized in some 
way. The current approach with calling tcpip_callback() all the time 
does not look like the right way to me.

Is anyone interested on collaborating on this? 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!

Simon