[RFC] Probing ttys by default

Lars Knudsen larsgk at gmail.com
Fri Mar 21 05:05:04 PDT 2014

On Fri, Mar 21, 2014 at 12:33 PM, Aleksander Morgado <
aleksander at aleksander.es> wrote:

> On Fri, Mar 21, 2014 at 12:11 PM, Lars Knudsen <larsgk at gmail.com> wrote:
> > First, can someone with a deeper knowledge of how the modemmanager probes
> > tell me (for a near term solution) if it's possible to report back some
> > magic keyword to the initial "AT" that will let the modemmanager release
> a
> > device instantly?
> >
> > Our problem is that we need to release very soon - and we want to support
> > Chromebook and Linux (in general) with our education platform (
> > www.empirikit.com ) - preferably without hacking our device to report as
> > something else - but we might be forced to to give an acceptable user
> > experience.
> Hum... hard to tell how you can do that without needing to change MM.
> The probing logic is more or less explained here:
> http://www.freedesktop.org/software/ModemManager/api/1.2.0/ch02s02.html
> Basically, if MM decides that needs to probe the device, it will start
> with AT probing (sends "AT" several times) to see if the port is an
> AT-capable port. If you don't want to get the port detected as AT, you
> can just ignore the "AT" command and not reply anything. Note that if
> you e.g. reply "ERROR" to that, the port will anyway get flagged as
> AT-capable. After the AT probing fails, it will try QCDM probing,
Bummer ;) - maybe this could be introduced as a possible bailout mechanism?

> sending a QCDM probe to see if the port replies correctly to it. If
> nothing is replied to the probe, the port will finally be discarded.
> This whole sequence may take up several seconds, as for each AT and
> QCDM probe we retry a couple of times. BTW, all this is for MM 1.x,
> the logic in MM 0.6.x is a bit different.
How many seconds for the version in the current Chromebooks (approx?).
As the Chromebooks are not easily possible to hack a blacklist in - AND they
are considered a std consumer device, they will be most exposed to this

> Which kind of TTY are you exposing? Is it a read-only tty (e.g. a
> usual GPS NMEA port) or a read-write one?

We are making a science lab sensor/controller to be used in (primarily)
developing countries' science education (K7-K12).  It's a two way
and we are basing it on Freescale's Freedom evaluation boards (e.g.
FRDM-KL25Z + mbed firmware)


> --
> Aleksander
> https://aleksander.es
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