Re: multiplex mode support

[Dan Williams <dcbw redhat com>]

On Thu, 2010-09-30 at 08:54 +0900, Marcel Holtmann wrote:
> Hi,
> 
> > Thanks, Dan! I have to deal with such a modem. Except the
> > implementation in kernel. I am interest in the implementation on user
> > space. The problem I may meet:
> > 1. How to get the data from the modem before other module get? From my
> > understanding, for ppp, after the link established, the data only flow
> > in kernel.
> > 2. How to feed the ppp packet into ppp module after decode the
> > multiplexing data?
> > 
> > My first thought to resolve this is using a pty. PPPd seems support
> > pty device. Multiplexing module get the modem data from modem device
> > directly and decode the data and feed the decoded data(if itis  the
> > ppp data) into the pty device which pppd opened.
> > 
> > This si practicable or not? Please give me some light.
> 
> we have done this in a nice library called GAtChat that implements the
> multiplexer and also userspace PPP support. It does everything for you
> including the AT command chat. Works pretty nicely. Just search for it.
> 
> It makes heavy use of GIOChannel and tries to pass data around as
> efficient as possible, but PPP on top of multiplexer is just not really
> a good idea in the first place. Too much encoding and decoding to do
> before you get anything done. We do want to use the kernel support for
> GSM MUX and PPP if possible, but so far we haven't gotten there yet.

Have you found the GAtChat PPP implementation (especially option
negotiation) to work pretty well with the modems that Ofono supports at
this time?  There's so many crappy device-side PPP implementations
around, but pppd is also a large pile of code that while it works pretty
well, has a few other issues...

Dan