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From:	"Rod Pemberton" <dont_have AT bitbucket DOT cmm>
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Subject:	Re: TSR issues (with code)
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Date:	Sun, 05 Feb 2006 13:50:05 GMT
To:	djgpp AT delorie DOT com
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"Brad House" <brad AT mainstreetsoftworks DOT com> wrote in message
news:43E587DC DOT 6080801 AT mainstreetsoftworks DOT com...
> Wow, thanks!  I think the crutch of the problem was I was
> using ds instead of es for the indos flag ... stupid stupid.
> Also, the realmode interrupt handler for int28 greatly helps
> my other needs as far as also needing to hook the BIOS calls
> as well. I need to create my own 'inBios' flag in order to make sure
> my TSR is bullet-proof (since I may need to call DOS and BIOS
> calls from within my TSR), so hooking those, incrementing an
> inbios counter, calling the previous hooks, then decrementing
> the counter should do that as per the Art of Assembly DOS
> reference on TSRs:
>   http://maven.smith.edu/~thiebaut/ArtOfAssembly/CH18/CH18-3.html
>
> Once I get that code squared away (and hopefully working flawlessly),
> I'll be returning that code to the public domain, so the next
> guy should be able to just plug the code into any relevant
> program.

Good luck.  As soon as you add write() back in, you'll hit the reentrancy
crash.  Probably some simple logic isn't correct.  Hopefully, it is an easy
fix, since I think the INDOS/IDLE flags are now correct.  But, if not, there
is an alternative way to deal with DOS reentrancy.  From DOS 4.0, you can
save and restore the Swappable Data Area (SDA) using int 0x21, ax=5d06h or
ax=5d0bh.  The SDA's size is larger if INDOS and smaller if idle.  I have no
further information on how this works other than Andrew Schulman's
"Undocumented DOS" has information.  I mention this because you want
"bullet-proof."  If you find anything on the web on this, other than Ralph
Brown's Interrupt list info, let me know.

Thanks and your welcome.

Rod Pemberton

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