Hi Japheth, in
http://www.bttr-software.de/forum/forum_entry.php?id=325
you write:
an update of Jemm is available. However, if the current version works
for you, there is no need to upgrade.
http://www.japheth.de/Download/jemm565b.zip
More details
It has turned out that the reboot strategies (standard and
altboot) of Jemm + FD Emm386 are totally different from what MS
Emm386 does. What's worse, the Jemm + FD Emm386 standard method
doesn't work on many machines.
With this update Jemm's standard method is fully MS Emm386
compatible.
related link: http://support.microsoft.com/kb/93366
However, the CHANGELOG gives a different impression:
-- v5.64
137. the ALTBOOT int15 hooking is now always done and ALTBOOT is dummy.
Background: We came to the conclusion that Jemm with altboot
works similar to what MS emm386 does without altboot. This
is also why Jemm often did not ctrl-alt-del properly at all
if you did not activate Jemm-altboot...
The old code was EITHER set breakpoint at :0 OR hook
int 15, while 5.65 does BOTH (catch jumps to :0
and hook int 15 to trap ctrl-alt-del keypresses). It is
interesting that the catch just puts an int 19 there,
is that a real reboot or just a fastboot in this case?
However, this is NOT fully ms emm386 compatible yet. In
MS emm386, altboot DOES have an effect. According to the
quoted page, ms emm386 normally hooks int 15 and :0,
and if ctrl-alt-del is detected, emm386 FIRST lets all
other int 15 handlers run and THEN shuts down itself and
reboots. If you use ms emm386 altboot, emm386 will instead
FIRST shutdown itself and THEN call other int 15 handlers,
because those might already do the reboot themselves and
you get a crash if you reboot without first shutting down
emm386. Note that ms emm386 altboot only has an effect if
int 15 is not called from within an UMB (i.e. if you do
not have KEYB loaded to UMB). Otherwise, shutting down
emm386 (disabling UMBs) before calling further int 15
handlers would be likely to have evil side effects...
Long story, read the MS page mentioned above :-)
So, what do we gain from the update? Answer: A lot :-)
MS EMM386 only needed altboot in very few cases, so it
is good that JEMM now behaves roughly like ms emm386
without altboot option. However, it is not good that
JEMM now simply ignores the altboot option.
It should show a warning that it does not yet implement
this option. Of course many people with FreeDOS or JEMM
do use altboot because they found out that they needed
it, but now that jemm without altboot behaves roughly
like ms emm386 without altboot, the roadmap of JEMM
should contain jemm with altboot should behave like
ms emm386 with altboot.
In short: If you needed altboot with ms emm386, you are
still out of luck. If you needed altboot with JEMM, you
no longer need it, and did not need it with MS either.
So many people will get better ctrl-alt-del now :-)).
Looking at the source, I see another change: Automatic page
frame location selection changed from 4k to 16k position
granularity, good idea :-). There also seem to be adjustments
in virtual A20 handling and UMB handling, could you explain
what has changed?
Eric
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