PLAY and RECORD at the same time

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Hi!

Gert Doering wrote:
> On Tue, Jun 29, 1999 at 02:41:34PM +0200, Marc SCHAEFER wrote:
> > Gert Doering <gert@greenie.muc.de> wrote:
> > > As far as I know, the current voice modem AT command sets do not allow
> > > simultaneous send and receive (DTMF works, but that's all).
> > 
> > > Marc?
> > 
> > Why do you ask me ? :)
> 
> You're the voice expert :-) (actually, I hoped Marc Eberhard is still
> around and could answer that...).

Well, sometimes... :-)

> > To my knowledge, most modems do not support bidirectionnal voice operation.
> This was what I was thinking as well, yes.

Correct. The only exception, I'm aware of, are some ISDN cards. Some of them
seem to support bidirectional voice.

> > Even if they would, mgetty doesn't support it.
> If the modems could do it, it would be a reason to implement support in
> vgetty... :-)

That's not easy to do. Vgettys event handling is well suited for such a
thing, but the problem is to get the handshake right. You don't want the
input or output direction to block the other one. So you either have to do a
fork() for a reader and writer process (common technique) or you have to
handle the flow control via the event mechanism. The latter is more
difficult to get right, but the more elegant and extensible solution. In any
way, it requires a lot of work. You have to handle two independent data
streams with full handshake control without side effects on each other.

Bye,
Marc (disappearing again...)
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