Re: Getting started (serial GPRS modem)

[Denis Kenzior <denkenz@gmail.com>]

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Hi Erik,

On 09/11/2012 08:17 AM, Erik wrote:
> Hi!
>
> I've been looking at ofono for quite some time now. A couple of years
> ago I wrote a lot of code to interface a GPRS modem. Now I need to do
> basically the same again and I wonder if ofono would be a good idea to use.
>
> The modem is not supported by ofono out of the box (no driver for it in
> the tree).
>
> First of all, I must say that I really miss some kind of "getting
> started" information on the home page. Maybe I have just not found it.
> Is there such a thing?
>

Formal getting started documentation is lacking at the moment. 
Documentation contributions are always welcome ;)

There are plenty of working examples to learn from however.

> Second, the modem is a serial GPRS modem connected through a serial
> line. This has to be farily common. Isn't there a simple way of just
> testing ofono without adding udev rules, writing drivers, etc? What I
> would like is basically to start ofonod with a path to the serial
> device, telling it to use only standard (not device-specific) AT commands.

We have tried that, unfortunately we have yet to encounter a piece of 
hardware that can be driven entirely using standard AT commands.  There 
are too many vendor commands and behavioral quirks that have to be 
accounted for.

>
> I don't think what I'd like to do is possible. So I added an udev rule
> in the form of:
>
> KERNEL=="ttyUSB*", ENV{OFONO_DRIVER}="nokia"

Are you picking a driver at random or is it indeed a Nokia modem?

>
> This gives me some indication that something happens when I start ofonod:
>
> ofonod[21742]: plugins/udev.c:add_modem()
> /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0/tty/ttyUSB0
> (atmodem)
>
> How do I proceed from here?
>
> test/llist-modems gives me nothing.
>
> Do the existing drivers check that the modem is actually a modem of that
> type (nokia in this case)?

No, but the list of modem drivers that support a serial port is only a 
subset of all the drivers available.  See add_modem() function in 
plugins/udev.c for more details.  The subset is currently limited to 
ifx, calypso, tc65, wavecom, sim900 and a few others.  These devices are 
true serial port devices and frequently require multiplexing, etc.

>
> I am not looking for anything fancy. I basically only want to set up a
> GPRS connection and maybe do operator selection.
> No voice, no SMS, nothing more.

If you're wanting GPRS on a true serial port based device, then you 
definitely need to write your own modem driver for it.  GPRS requires 
multiple AT ports to drive successfully which requires multiplexing 
(e.g. via CMUX).  Multiplexing details are frequently vendor-specific, 
so these have to be handled in your driver.

Regards,
-Denis