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From: connery@bnrmtv.UUCP (Glenn Connery)
Newsgroups: net.micro.pc
Subject: Re: DOS re-entrancy
Message-ID: <276@bnrmtv.UUCP>
Date: Tue, 11-Mar-86 15:04:03 EST
Article-I.D.: bnrmtv.276
Posted: Tue Mar 11 15:04:03 1986
Date-Received: Fri, 14-Mar-86 06:25:09 EST
References: <103@nvuxr.UUCP> <23900011@siemens.UUCP>
Organization: Bell Northern Research, Mtn. View, CA
Lines: 29

> 
> There is a flag buried in the internal data area for MS-DOS called INDOS.
> A 0 value indicates that MS-DOS is not currently executing in a critical
> section. Any other value indicates that you can not make a Int 21 call.
> 
> To find out the current value of this flag:
> 
> 	1. Before interrupt processing starts execute the GET_INDOS_FLAG
> 	   function. This is function 34h in MS-DOS.
> 	   (i.e. AX = 34h when doing the Int 21)
> 
> 	2. Upon return you don't get the flag but rather a pointer to
> 	   it in ES:BX.  ES = the segment address and BX = the offset
> 	   address of the INDOS flag.
> 
> 	3. When the interrupt occurs directly test this byte from the
> 	   interrupt handler to determine if calls to MS-DOS are
> 	   allowable. You will have to determine appropriate actions
> 	   if the interrupt occurred during a critical section of MS-DOS.
> 
> Hope this helps.
> 
> Jim Vallino
> {allegra,ihnp4}!princeton!siemens!jrv

-- 

Glenn Connery, Bell Northern Research, Mountain View, CA
{hplabs,amdahl,3comvax}!bnrmtv!connery