Said Tom Ehlert <te@dr.. - 2013-07-13 17:31 :

> I can reproduce the bug; reason so far not found
Do you mean, not identified in the source, or what ?
 
> it would be helpful for the uninitiated if you could share
> which MCB and which internal variable to adjust

I /thought/ I had provided /enough/ information.. Well, here we go,
note that I'm going yo decribe how to work around the broken kernel, /not/ how 
to fix the kernel code itself!

Not sure this is the place for this level of detail, but Tom asked for it...

To repair the memory chain after 1) the XBDA has been removed from
mem_top 2) DOS UMB management has been (mis)installed, a
device driver (3) would simply have to :

a) lift the (erroneous) 'segment of upper memory link (Word at offset
8C in DOS Sysvars segment, cf. int 21/52). It /was/ the segment
immediately preceding the /original/ XBDA. Let this be called P
Change that sysvar from P to 9FFF.

b) Copy the MCB (erroneously) built by FreeDOS,, from paragraph P
to memory paragraph 9FFF , then adjust SIZE by substracting 
(9FFF - P). The resulting MCB will point to the first actual MCB
in upper mem.

That's the :scheme to /work around/.the bug/ in excruciating detail ;=)

OTOH for properly /fixing the kernel code/ I guess you'll have to lookup
and follow specially how the variables ram_top & ebda_size are
initialised and adjusted, hint : starting in 'config.c'... 


>and being not so secretive about your project might even rise motivation

I think I have already said, I am not at liberty to disclose more at the 
moment. Besides, I hardly perceive how this would affect the validity 
of a bug report, made in good faith.

Cheers

-- 
Czerno


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