interface for modems with out of band signalling

interface for modems with out of band signalling

[Oliver Neukum]

Hi,

I have got a question about modems which use the AT command set, but
don't use in band signalling like true rs232 modems. Would two device nodes
per communication channel be a good interface?

	Regards
		Oliver

Re: interface for modems with out of band signalling

[Phillip Susi]

Oliver Neukum wrote:
> Hi,
> 
> I have got a question about modems which use the AT command set, but
> don't use in band signalling like true rs232 modems. Would two device nodes
> per communication channel be a good interface?

Huh?  What do you mean "don't use in band signaling"?  If you are asking 
how you issue AT commands to the modem while connected, you have to 
break to command mode.  IIRC, this involves sending a special break 
character or two with the correct delay between them, or flipping one of 
the RS232 handshake lines.

Re: interface for modems with out of band signalling

[Oliver Neukum]

Am Freitag, 15. Dezember 2006 16:53 schrieb Phillip Susi:
> Oliver Neukum wrote:
> > Hi,
> > 
> > I have got a question about modems which use the AT command set, but
> > don't use in band signalling like true rs232 modems. Would two device nodes
> > per communication channel be a good interface?
> 
> Huh?  What do you mean "don't use in band signaling"?  If you are asking 
> how you issue AT commands to the modem while connected, you have to 
> break to command mode.  IIRC, this involves sending a special break 

No, I am talking about how to support modems which don't have a
command mode. These USB modems don't accept AT commands
through the same channel as data. They take them encapsulated in special
command messages to endpoint 0.
How do I export this capability to user space? I am thinking about having
two device nodes. But there may be a driver setting another precedent.
Therefor I am asking.

	Regards
		Oliver

Re: interface for modems with out of band signalling

[Alan]

> No, I am talking about how to support modems which don't have a
> command mode. These USB modems don't accept AT commands
> through the same channel as data. They take them encapsulated in special
> command messages to endpoint 0.
> How do I export this capability to user space? I am thinking about having
> two device nodes. But there may be a driver setting another precedent.
> Therefor I am asking.

ISDN4Linux provides a fake modem emulation in kernel space. The Nokia
phone drivers provide a user space manager which provides the interface.

So you've got precedents for both. If it's simply a case of splitting AT
commands off from the data and spotting guard bands and +++ you might
want to do it kernel side, if the second endpoint takes its own set of
phone control messages I guess its hairier.