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PROSPEED.PAT
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1990-05-23
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5KB
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146 lines
Quarterdeck Technical Note
Patching COMMAND.COM on the NEC ProSpeed 386 to
prevent Exception #13 messages when QEMM-386 is
active
Background: The NEC ProSpeed 386 comes with a
version of MS-DOS that is modified to accommodate
certain hardware features of the system. In
particular, both IO.SYS and COMMAND.COM issue one
protected mode instruction to read the contents of
an 80386 control register. We believe that this
command is part of an attempt to determine whether
the system is attached to its optional "docking
station," which can contain additional hardware for
the system's use. QEMM-386, Quarterdeck's 386
memory manager, is loaded after IO.SYS but before
COMMAND.COM; if QEMM-386 is in an ON state (which
can happen for various reasons, including the use
of QEMM.SYS's RAM or ROM parameters), the machine
will be in virtual 8086 mode when COMMAND.COM
issues its protected mode instruction, and QEMM-386
will halt the system and pass along the "Exception
#13" (protection exception) that the 80386
processor generates in such circumstances.
Typically the user sees this message after the
completion of the CONFIG.SYS routine and before the
AUTOEXEC.BAT executes; the message can also occur
at various other times when COMMAND.COM is loaded
again. The user is given the option of continuing
operation after the Exception #13 message, in which
case QEMM-386 turns itself OFF and attempts to
restore the state of the computer as it was before
QEMM-386 was loaded; the difficulty of restoring
the system properly can result in instability after
the Exception #13 message is passed.
The following procedure is intended to prevent
the "Exception #13" messages that are generated
after the CONFIG.SYS file completes loading (and at
other times) on the NEC ProSpeed 386 when QEMM-386
is in the ON state.
-------------------------------------------------
1) Make a bootable DOS diskette with the DOS that
comes with the NEC machine. We are about to
alter the COMMAND.COM on the machine's hard disk;
the COMMAND.COM on the bootable floppy will serve
as a backup in case this operation fails.
2) Go to the DOS directory on the hard disk and
type:
DEBUG C:\COMMAND.COM
(If your COMMAND.COM is not located in the root
directory of the C: drive, change the path
accordingly.)
Hit the Enter key; you should the the DEBUG
prompt, which is a hyphen.
3) At the DEBUG prompt, type:
S 100 L 6000 F 20 C0
Hit the Enter key; DEBUG should return a segment
address and an offset:
xxxx:yyyy
4) At the DEBUG prompt again, use the address
and offset that was just returned to give the DEBUG
command:
E xxxx:yyyy EB 1
The address that DEBUG returned in step 3 should
be used in place of the address xxxx:yyyy, which we
use as an example. Hit the Enter key; the DEBUG
prompt should return in a moment.
5) At the DEBUG prompt, type
W
Hit the Enter key; DEBUG will announce that it is
writing a certain number of bytes, then it will
return the DEBUG prompt.
6) At the DEBUG prompt, type
Q
Hit the Enter key to exit DEBUG and return to DOS.
--------------------------------------------------
If the system fails after you perform this patch,
use the bootable DOS floppy to start the system,
then at the A: prompt, type:
COPY COMMAND.COM C:\
(If your COMMAND.COM is not located in the root
directory of the C: drive, change the path
accordingly.)
You may then wish to try the above procedure
again, in case a mistake was made.
Our current belief is that this patch may
interfere with the machine's normal operation if
you are loading the program VM/386. Otherwise, we
expect no problems as a result of this patch.
* * * E N D O F F I L E * * *