Thanks a ton Sylvain ... you rock !!!! I am now confident enough to get my hands dirty with the code, since logically the pieces seem to be fitting in ....
Thanks a ton again, I will go through the documentation, and let you know for sure how things go .. Thanks and Regards, Ajay On Fri, Aug 21, 2015 at 7:03 PM, Sylvain Rochet <[email protected]> wrote: > Hi Ajay, > > On Fri, Aug 21, 2015 at 06:35:18PM +0530, Ajay Garg wrote: > > On Fri, Aug 21, 2015 at 5:46 PM, Sergio R. Caprile <[email protected]> > > wrote: > > > > > What I would do, if I were in your shoes, is to write my app for lwIP, > > > and then either use PPP for those TCP/IP capable GPRS modules > > > > You mean even if we use lwIP, we would be dependent on the TCP/IP (stack) > > of the GPRS module? > > That would defeat the purpose of using lwIP at the first place. > > > > I am sure I am having a massive misunderstanding .. > > No, once your GPRS modem is in PPP data mode, lwIP take care of all > the PPP/IP stuff. > > > > > and a > > > layer-2 interface (netif) for the other ones. > > > This way, your app is always the same and you only change code for what > > > is below layer-3. You'll have to write your own netif, though. > > > lwIP is a TCP/IP stack which communicates to "the outside world" via > > > interfaces called "netif". Basically you can run it on top of > everything > > > where you can write a netif for. > > I don't understand why Sergio is proposing that, lwIP embeds a full > featured PPP stack and all GPRS modems I know are able to do PPP. > > > > I went through http://lwip.wikia.com/wiki/PPP > > > > We majorly need to code the "read" and "write" methods, right? > > In our case, if we are interfacing the GPRS-module with the > > Micro-controller via UART, then this would mean simply reading-from / > > writing-to UART, right? > > Right! :) > > > > Also, one another question (this is majorly due to my lack of > understanding > > of nitty-gritties of the protocols) :: > > > > For using TCP/IP/PPP/Serial, we simply have to bring the GPRS-Module into > > "Connect OK" mode (by using primitive AT commands). Thereafter, we need > to > > switch the GPRS-module into "data mode" and then leave it to lwIP to set > up > > the TCP/IP contexts, and later allow the usage of sockets. > > > > Is my understanding of the algorithm (at a broader level) correct? > > That's correct. You don't even need to switch your GPRS to data mode, > once "CONNECT OK\r" is sent your modem already switched to data mode and > you should initiate the PPP session. > > > The most up to date PPP documentation is embedded into the doc directory > of lwIP sources: > http://git.savannah.gnu.org/cgit/lwip.git/tree/doc/ppp.txt > > If anything is missing or unclear, told me and I will try to improve it. > > > Sylvain > > _______________________________________________ > lwip-users mailing list > [email protected] > https://lists.nongnu.org/mailman/listinfo/lwip-users > -- Regards, Ajay
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