Mainly reutilizing code from ublox C027 support lib.
As we are using external PDP context, i.e., an external IP stack,
we will pass username and password to underlying stack running PPP.
We only support CHAP as the authentication protocol.
POSIX poll() provides a mechanism to attach a POLL_HUP event
if the modem or device hangs up on you. POLL_HUP and POLL_OUT are
mutually exclusive. We poll in the PPP_input() routine if the modem
hung up. If it did we stop the data consumption, close PPP and go back
to the driver for reserruction of AT parser and subsequent retries or
application specific actions.
This is achieved by attaching an interrupt to the DCD line of the modem.
When DCD line goes high (off), we have lost the carrier. So we record an
POLLHUP event using _poll_change().
In case of carrier lost, we would like to inform PPP data pump.
That involved setting up link status flag down semaphores.
mbed_lwip_bringup() and mbed_lwip_bringdown() had been Ethernet specific only.
We extend these routines to support PPP as well. Currently we support only one interface
at a time. However, future enhancement to multi interface support should be trivial.
mbed_ppp_init() is extended to take a function ptr.
ppp_lwip will call this callback upon a change in ppp link status.
in the beginning, the Ublox driver waits until the PPP link is established properly.
We introduce here mbed_trace to ppp_lwip shim layer.
If for some reason, FEATURE_COMMON_PAL is not included in the build,
dummies for trace functions are provided.
This is a glue layer between LWIP PPP implementation and a device type FileHandle
stream. This enables an external interface which has a FileHandle, utilize LWIP network
stack via PPP, e.g., Cellular device, WiFi chips etc.
Its totally transparent to external device. Only thing this layer is interested in, is a
FileHandle. Similar is true for for the external device, it just hands over its stream to this
PPP layer and rest of the magic is done by this layer.
Hasnain Virk
Kevin Bracey