Re: [lwip-users] Advise on PPPoS implementation

[Raivis]

Hi,

I tested with UDP, and it didn't work.

But, whole day, I've been working on porting the PPP GSM interface to unix system. Took me a while since, I hadn't worked with LwIP at this detail before.

Thankfully, I can confirm it works on my linux machine, but not on stm32. So I've probably made a mistake somewhere with stm32.

Now that I have a working system, I can compare it to stm32 and see what goes wrong, and try to solve it. My main suspect is the way I'm using HAL layer for serial transmission. (which is still odd, since PPP get's the IP)

In any case, thank you all for your help.

I also wanted to add that contribution package was a massive help and once you know what you are looking for, the documentation is nicely structured and I was able to find exactly what I need.

Best Regards.

Raivis Strogonovs

On Thu, Nov 2, 2017 at 5:48 PM, Sylvain Rochet <address@hidden> wrote:

Hi,

On Thu, Nov 02, 2017 at 05:02:36PM +0000, Raivis wrote:
> That's a very good, point, I've been so frustrated that it didn't occur to
> me that I can just print the packet in my serial function.
>
> Apologies I somehow over glanced your suggestion before.
>
> I enabled the PPP_DEBUG and PRINTPKT_SUPPORT, and removed all filters from
> ppp_dump_packet() in utils.c, leaving just "pp_dbglog()"  function call.
>
>
> From my inexperienced point of view, the PPP side seems to work fine I
> guess.

It is, pppos_netif_output() is the last step in the lwIP PPP stack, it
means (if it succeed, which is the case here), that your serial output
callback was called.


> Is it something to do with netif?

I don't understand to which scope this question apply; The netif is
properly configured for me, we can undoubtfuly see the TCP SYN attempt
in the debug log, meaning the packet goes down all the stack up to your
serial low level writer.

If you are talking about your low level flow serial driver, it looks
fine from here, you already said you saw the TCP packet properly sent on
wire.

However, there might be some missing dark magic in your dialup
chatscript ("AT" commands) before starting the PPP session. Your modem
accepts the PPP session and set a apparently usable IP address so it
should work but, well, some of these modems (all?), especially cellular
ones, have some quirks[*] in their firmwares.

   [*] I'm saving a strong word here


Maybe you could try with UDP first instead of TCP; I don't think it
would help in this case but we never know.


Sylvain

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