CellularDevice::get_default_instance() is a weak method and is overriden
by either a default construction provided in the code or by application
at some stage. This method needs to be flagged otherwise using another
driver will be hindered by the default overriding of this driver.
For default construction of the driver, it would be necessary to define
the pins. However as we don't know the correct pins, until/unless user
sets them up for us. So it makes sense to mark the pins as NC. It would
be easier to debug if the pins are set to NC if user forgot to set them
up.
To make this driver more useful, we needed to do some changes. The
wirings for the modem can differ on the board so we also need to be
flexible in our approach.
It is now mandatory to provide the power pin and pin polarity in the
constructor alongwith the file handle. Reset pin is optional.
Standard 3GPP TS27.007 states that the AT+CGSN command can optionally
have type parameter that determines the output. However Quiectel EC2X
series doesn't accept parameters. We need to reflect that in the
cellular properties setup.
Provides basic power up / power down sequences for Quectel EC2X series
modems. Can be used in PPP mode. For using the on-board IP stack, we
will need to add and implement classes that provide context.
Driver constructor takes power and reset control pins along with the
FileHandle. A default construction is provided which can be chosen by
the application in its mbed_app.json. Otherwise the user is free to
construct as per demand.
Hasnain Virk