Re: IIgs RAM drive question

[CUTblakeney@home.com (Jeff Blakeney)]

On Mon, 20 Dec 1999 22:54:15 +1300, dempson@actrix.gen.nz (David
Empson) wrote:

>My point was that it is ProTerm (and other programs which have this
>feature) which are doing something special here.  It is _not_ a built-in
>feature of the IIgs.

It is a built in feature of the IIgs.  No modifications need to be
made to the IIgs hardware to allow this to happen so it is, by
definition, built in.

Admitedly, the designers made not have done this intentionally but
that is how it turned out.  This is nothing new to the Apple II as
programmers have been finding neat side effects to the designs of the
machines since the first machine came out.  :-)

>There is no standard software (either system software or firmware) which
>lets you use the serial hardware, except the built-in serial firmware,
>and the firmware is only available if slot 2 is set to "Modem Port" (or
>"Printer Port" on a ROM 3).

But the ways to access the serial hardware directly are documented
just like the firmware method is.  Programmers have always had the
choice to access the hardware directly or use the firmware.  Using the
firmware is supposed to guarantee that your program will continue to
work even if the serial hardware is changed but using the hardware
directly will almost certainly cause the program to not work if the
serial hardware is changed.

>Any program which lets you use the modem port despite slot 2 being set
>to "Your Card" must be implementing its own driver which bypasses the
>firwmare.

Yes and they are using documented methods to create their own driver
and this method requires that the hardware design of the IIgs allows
programs to directly access the serial hardware regardless whether
slot 2 is set to "Modem Port" or "Your Card".

>As for "doing anything that the hardware and firmware won't allow": the
>IIgs serial hardware is designed in such a way that it doesn't depend on
>the slots, so a program which wants to bypass the firmware can do this
>if necessary (as long as it doesn't interfere with something else using
>the serial hardware, such as AppleTalk).
>
>It has nothing to do with the firmware, just the hardware.

Well, I kept saying "hardware and firmware" because they are very
closely tied together and the way the firmware works when the slot is
changed between the "Modem Port" and "Your Card" is relevant.

However, you seem to be agreeing with me that it is mostly the
hardware design that allows you to access the serial port hardware
directly even when the firmware has been told that slot 2 is set to
"Your Card".  This still says to me that Adalbert was right that it is
the hardware that allows you to do this rather than any particular
piece of software.  The software is simply taking advantage of a
hardware feature and isn't providing some capability that the hardware
doesn't allow because that would be impossible.

Saying that ProTERM is providing that ability is kind of like saying
that MUG! allows you to access MFM encoded disks on hardware that
isn't capable of reading MFM encoded disks.  It simply can't happen.
The hardware has to support what the software wants to do.

Maybe this is one of those things that depends on how you look at it
but it sure seems pretty straight forward and logical to me which is
why I've been defending my position so strongly.  That and the fact
that I'm a hardware designer as well as a programmer so I know that I
can't write a program that does anything that the hardware it is
running on is incapable of doing.  :-)

+------------------------------------------------------------------------+
| Jeff Blakeney - Dean of the Apple II University in A2Pro on Delphi     |
|                    Delphi Apple II Forums Web Pages                    |
| A2: http://www.delphi.com/apple2   A2Pro: http://www.delphi.com/a2pro  |
+------------------------------------------------------------------------+