No documentation is not something the lwIP people seem to excel in (, nor making decent looking websites).
But there is a contrib zip file at download.savannah.gnu.org/releases/lwip/ with example code.
I used the Windows port, and added some glue to use a real com-port instead of a named pipe (guess they run it in virtualbox or the like, sio.c).
The Windows example has PPP support (might need some defines), I altered startup to:
sio_fd_t ppp_sio;
ppp_sio = sio_open(6); // com port number
if (ppp_sio != NULL)
{
printf("pppInit\n");
pppInit();
pppSetAuth(PPPAUTHTYPE_ANY, "Vodafone", "Vodafone");
printf("pppOpen\n");
sio_write_string(ppp_sio, "ATE0\r\n");
sio_expect_string(ppp_sio, "OK\r\n");
sio_write_string(ppp_sio, "AT+CGDCONT=1,\"IP\",\"office.vodafone.nl\"\r\n");
sio_expect_string(ppp_sio, "OK\r\n");
sio_write_string(ppp_sio, "ATD*99***1#\r\n");
sio_expect_string(ppp_sio, "CONNECT 115200\r\n");
do_sleep(1000);
pppOpen(ppp_sio, pppLinkStatusCallback, NULL);
}SIO GLUE stolen from:
metsahovi.fi/~jwagner/iBob/g … etif/sio.c