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SubjectRe: Turning lucent winmodem into soundcard (RT-Linux -when?)
Jon Bright wrote:

> Jamie Lokier wrote:
>
> > There are many reports of winmodems generally working quite badly in
> > Windows. Occasional line drops, that sort of thing. I don't know if it
> > applies to the models we're working on at the moment.
>
> I've worked with several different varieties of Winmodem, and of all of them,
> the Motorola SM56 seems to suck most (or, at least it's driver does). Do
> anything that will be tying the machine up for a little while - compiling,
> rendering a large page in Netscape, etc., and presto, a line drop.

A lot of people seem to think Winmodems are all dumb. Actually, most have a DSP,
and only relegate the microcontroller functionality to the host CPU. This doesn't
place a huge burden on the host. In fact, considering the inefficient clunky way
you have to work through a UART to a "real" modem, it probably doesn't incur any
significant overhead, if it is done right. The observation that most Winmodems
are troublesome reflects the fact they are not done right. It doesn't mean the
basic technique has any problems.

The Motorola modems are different. They are truly dumb, like the AMR ports
appearing on many new motherboards. The board is nothing more than a line
interface and codec. The high demands this puts on the host CPU explain what you
observe. With a fast modern machine their average demand may be OK. The killer is
they have little or no buffering, and the host CPU must keep up with the flow of
interrupts at all times, or completely scramble its signal processing. That's
tough to achieve, and as you observe, they often fail.

> On an unrelated note, and further off-topic - does anyone know of a modem that
> will *currently* work with Linux, and which returns 'RING' or 'RINGING' when
> the other end is ringing (and ATX4 or similar is selected)? It's a bit of an
> unusual requirement, I realise, and seems to be something modem manufacturers
> have silently stopped doing. I'm on the list, but I think replies would be
> better directed straight to me.

This is almost impossible to do reliably. There are now so many ring back tones
in use, and many of them are "proprietary". Would detecting only the major
nationally standardised ring backs and missing the others be very useful? I don't
know about this being dropped. I've never seen a modem that does it. They only
output RING when the local line is ringing.


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