Date: Sun, 29 Jul 2001 10:47:09 +0300 (IDT)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender: eliz AT is
To: Raf256 <raf256 AT go2 DOT pl>
cc: djgpp AT delorie DOT com
Subject: Re: Odp: Dos program with multitasking
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On Sun, 29 Jul 2001, Raf256 wrote:

> My question is - can You spare litle of Yours time to help me with writting
> UPT ?

I can certainly try to answer questions if you post them.

> How can I exacly (maybe small example) write programs using method #2 to
> make multitasking ? I don't realy need so much to run in background DOS
> 16-bit programs from my shell, but  need to run my applications written in
> DJGPP. I think that it can work like this :
> UPT.EXE hooks some unused interrupt numer INT and spawns APPL.EXE
> APPL.EXE hooks timer interupt. Each i.e. 0.1 s it's using interrupt INT to
> return controll to main program UPT.EXE. It's alsow uses INT with special
> values of AX,BX... to cal UPT API, for example in timer interrupt - mov ax,1
> int INT - returns controll to UPT each 0.1s, and in main program  - mov ax,2
> int INT  - draws new window etc...

It seems you are trying to do exactly what I said DPMI spec disallows:
to switch tasks from the timer interrupt handler.  This won't work.