Linux modem example

This is an experimental port of the esp_modem to linux. It mocks some IDF functionality with port/linux layers (used for modem host test suite) and implements esp_netif, which supports tun interface and uses lwIP ppp implementation to parse or wrap IP packets to be send/receive over PPPoS, i.e. over the modem serial line.

Configuration

• Set path to the lwip and lwip_contrib repositories as environmental variables:
  • LWIP_PATH: path to the lwip repository
  • LWIP_CONTRIB_PATH: path to the lwip_contrib repository
• Create a tun interface using make_tun_netif script.
• Set SIO dev name directly in the code: This is the serial port which is the modem connected to
• (Set the tun device na interface name in the code: Not needed if the device was created using the script above.)
• Build and run the example (no elevated privileges needed)
• Experiment with the network, after getting the IP from the modem device
  • directly in the code
  • in the system (need to set tun interface IP, dns servers, and routing the desired traffic over the tun interface)