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2134

Category: DOS kernel

INT 21 - DOS 2+ - GET ADDRESS OF INDOS FLAG

	AH = 34h
Return: ES:BX -> one-byte InDOS flag
Notes:	this function executes on the DOS stack, and thus cannot be called
	  while another DOS function is already executing; you should use
	  this function once at the beginning of the program and store the
	  returned pointer rather than calling it when requiring DOS access
	the value of InDOS is incremented whenever an INT 21 function begins
	  and decremented whenever one completes
	during an INT 28 call, it is safe to call some INT 21 functions even
	  though InDOS may be 01h instead of zero
	InDOS alone is not sufficient for determining when it is safe to
	  enter DOS, as the critical error handling decrements InDOS and
	  increments the critical error flag for the duration of the critical
	  error.  Thus, it is possible for InDOS to be zero even if DOS is
	  busy.
	SMARTDRV 4.0 sets the InDOS flag while flushing its buffers to disk,
	  then zeros it on completion
	the critical error flag is the byte immediately following InDOS in
	  DOS 2.x, and the byte BEFORE the InDOS flag in DOS 3.0+ and
	  DR DOS 3.41+ (except COMPAQ DOS 3.0, where the critical error flag
	  is located 1AAh bytes BEFORE the critical section flag)
	for DOS 3.1+, an undocumented call exists to get the address of the
	  critical error flag (see AX=5D06h)
	this function was undocumented prior to the release of DOS 5.0.
SeeAlso: AX=5D06h,AX=5D0Bh,INT 15/AX=DE1Fh,INT 28

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  Copyright 2000   by Ralf Brown     Updated Jul 2000