Re: IEEE once more.

From: Christer Palm (
Date: 2001-05-12 15:35:24

Hi there!

Ruud Baltissen wrote:
> > 3) Consider a serial talker, to an IEEE-listener. The talker happily
> >    starts transmitting data, which I gateway to the IEEE bus. If, at a
> >    given time, the controller had enough, and asserts ATN, this will
> >    probably be in the middle of a byte being transfer on IEC. How should I
> >    handle this? In a 'best case scenario' :), this will result in the IEC
> >    talker 'talking' one byte too much.
> This scenario only happens if you program two FD's to exchange data.
> The situations we know of the Controller, the computer in this case, is
> always either the talker (SAVE, PUT) or listener (LOAD, GET). As Talker
> it can stop transmissions and send a UNLISTEN. This means the file
> won't be complete but the FD doesn't know. As Listener it could not
> respond to the handshake signals causing the FD to terminate the
> process. Then the computer could send a ATN.
> Writing the above the thougfht occured to me: what reason could the
> computer have to send an ATN in the middle of a normal proces? The
> only system doing such things is a multi-tasking one.

Almost. As the _Controller_, it can send UNLISTEN.
The controller may very well facilitate a data transfer between two
other devices (Yes, that works in reality, too!).

The controller can issue a command at any time, and if the controller is
not a listener or a talker, this may just as well happen in the middle
of a transfer (It's actually up to the application or user issuing
OPEN/CLOSE). The transfer will probably mess up, but this is not handled
in current implementations, so there's no need for you to handle that in
any special way either.

> > I want to keep the thing as simple as possible, preferrably even stateless.
> May be a blunt thought: what does it matter! You only have to convert
> things, not to interprete them :)

Exactly - unless you'd want to translate device addresses, etc, you
could just hose everything without further interpreting the contents of
the data stream or the sequence of events.

Christer Palm
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