Re: Mobile broadband connects to wrong USB device

[Dan Williams <dcbw redhat com>]

On Thu, 2009-01-15 at 17:46 +0000, Rick Jones wrote:
> Hi Dan
> 
> --On Wednesday, January 14, 2009 18:29:51 -0500 Dan Williams
> <dcbw redhat com> wrote:
> > On Tue, 2009-01-06 at 16:03 +0000, Rick Jones wrote:
> > > 
> > > a) it requires an initial <CR> otherwise it fails to see a clean
> AT
> > > command and doesn't respond - resulting in an init. timeout.
> > 
> > With this, my Sierra 860 doesn't respond and times out.  Were you
> ever
> > able to find out from the MobileStream guys why this might be
> required?
> > It might also be something that NetworkManager isn't doing when
> setting
> > up the serial port.  Does USBModem need specific serial port
> settings?
> 
> I didn't get much response from MobileStream, and also the problem
> doesn't happen on Windows :(. It seems to be some interaction with the
> Linux USB/serial driver, because I can prove the problem simply by
> connecting to the modem with telnet to /dev/USB0. The first command
> after connection is ignored. I thought initially that it needed to
> receive 2 AT commands before it would respond, but in fact it just
> needs \r before the first AT. I suspect that it picks up a bogus byte
> or two when the connection is opened, and thus the first AT is not
> seen as starting a new line, and hence ignored.
> 
> > > b) its initial CREG state is 1, meaning that NM gets incorrect
> > > responses to its CREG queries later in the conversation. It
> requires
> > > +CREG=0 in the init string.
> > 
> > With this also, my Sierra 860 doesn't respond and times out.
> 
> Hmmm,  that's a blow, I would have thought that a modem that responds
> to CREG queries would allow +CREG=n.
> 
> > > By hacking these fixes into the init string it works fine. It's a
> soft
> > > modem running in a Palm Treo handheld: USBModem by MobileStream.
> At
> > > least one other poster on this list is using (or trying to) the
> same
> > > software.
> > 
> > What's the init string you currently use?  Long ago you mentioned:
> > 
> > AT&F\rATV1 X4 &C1 +CREG=0
> > 
> > Is that still correct?  Or can you move the AT&F after the \r?
> 
> I've changed it to \rAT&F V1 X4 &C1 +CREG=0.         It will also
> accept E0 and +FCLASS=0, but I overwrote those because I tweaked the
> embedded string in binary and couldn't extend it - those settings
> happen to be the defaults in USBModem.

Applied to git head, will get cherry-picked to 0.7 too.  Please test it
out if you can.

Dan


> > > Regarding ATZ v. AT&F, I believe the latter should always be
> > > supported, as it is a full reset. ATZ restores to settings saved
> using
> > > AT&W, but if that's never been used it's the same as AT&F. If AT&W
> is
> > > not supported, then ATZ may not be either; and if you don't use
> AT&W
> > > to save settings (does NM?) then there is no reason to use ATZ.
> > 
> > The Sierra 860 also doesn't like AT&F *at all*.  Whee!  If we can
> put
> > together an init string that works for now, we can add it to the
> bottom
> > of the list.
> 
> USBModem works with ATZ or AT&F, but I noticed a post from someone
> else saying their modem didn't like ATZ. I was recalling my memories
> of programming "real" modems, where AT&F was always the full "factory
> reset", and hence the only thing that could be guaranteed to put the
> modem into a known state.
> 
> This is always the problem - somewhere along the line someone
> re-interprets the "standard", so it's never quite as standard as we'd
> all like :-/.
> 
> Maybe it's possible to have an init string that's close to universal
> at the moment, but I think everything said above illustrates that it's
> probably impossible to get a single string that works (and will work)
> for everything. To deal with the security issue, how about a
> configuration file writable only by root, containing a list of
> possible of init strings? This would be shipped with a selection of
> strings to cater for currently known variants, which the user can
> select from. In the case of a user having an even more oddball device,
> with tech knowledge and admin privilege they can add other entry.
> 
> Getting closer ....
> 
> Cheers, Rick