Hi,
No, the connection is not even established with the remote server.
In the debugger I see, that netconn API definitely invokes the PPP interface, and goes into my serial write function, but no connection is established whatsoever.
Note I tested whether the server works via telnet.
Another thing is, I've noticed that the GSM module is not talking back at all when transmitting TCP packets. Looking through the RX/TX data from logic analyzer, it seems I'm sending data to the module, but it never sends anything back.
Which is very odd, since the PPP connection gets established, and during that, I can confirm via logic analyzer that the module and micro-controller are chatting back and forth.
I'm beginning to think the issue might be one of these:
1. O2 is blocking my connection, and not establishing TCP connection
However, I'm not so sure about this, because the A6 modem has their own PPP stack, and I can connect to my server via their TCP commands and send data.
I'm not able to use their stack, because I'm very interested in getting PPP working as a learning stepping stone, ultimately, I'll be using a satellite modem which requires PPP to establish a connection to my server.
2. Faulty modem. I ordered another one just to test it, instead of A6, I'll test with sim800l. I've noticed that this one doesn't comply with it's own datasheet AT commands. e.g. ATE0 should disable echo, and it doesn't.
3. ST implementation of LwIP is faulty. I'm using LwIP version which comes with CubeMX. I've noticed it is version 2.0.0 instead of 2.0.3.
Any other ideas, what I should be looking for or what could be the cause?