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amiga.dev/janus #308, from jrush, 1666 chars, Thu Sep  7 23:55:36 1989
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I have uploaded a utility called USE_A000.ARC that will enable Janus
users to address their Bridgeboards at A000 and still function fully.

Electrically speaking, the handler can be mapped to A000, D000 or E000
(XT) or only A000 or D000 on an AT Bridgecard.  A limitation is that
the range of addresses a PC BIOS scans for ROM extension signatures is
C000 up to F600 (top end varies among clone makers).  This means that
the handler will not be initialized (and thereby linked into the system)
when placed at A000.  However, it would sure be nice to be able to use
A000 since there is fierce competition for address space in the PC's
upper address area among plug-in boards.

Be warned, however, that an EGA video card uses the A000-BFFF range
of memory and will conflict with such a choice.  I do not know about
VGA cards.

.More..

                        The Desired Solution
                       (Please consider, Bill)

The proper way to implement this is for Commodore to enhance their
Janus software in the following manner.  While the handler memory
moves around, the 16 Kb or parameter memory is fixed at F000 (XT
or D000 (AT).  These addresses are in the range scanned by the BIOS
for ROM extensions (the D000 certainly is, the F000 I think is) and
could be used to gain control during the bootup process.  It would
be possible for PCWINDOWS to realize that the PC preference setting
is for A000, and to stuff a dummy ROM extension in an initially-unused
portion of parameter memory that consists solely of a proper signature
and a far jump to the real ROM extension at A000.  The dummy ROM extension
would then be overwritten as the parameter memory is used.

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