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<TITLE>Int 21/AH=34h
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Int 21/AH=34h - 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
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<h2>Int 21/AH=34h
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<h3><font color=#C00040>DOS 2+ - GET ADDRESS OF INDOS FLAG</font></h3>
<PRE>
AH = 34h<br>
<p><b>Return:</b><br>ES:BX -> one-byte InDOS flag
</PRE>
<p><b>Notes:</b>
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.
<p><b>See Also:</b>
<a href="rb-3023.htm" tppabs="http://www.ctyme.com/intr/rb-3023.htm">AX=5D06h</a> - <a href="rb-3028.htm" tppabs="http://www.ctyme.com/intr/rb-3028.htm">AX=5D0Bh</a> - <a href="rb-1706.htm" tppabs="http://www.ctyme.com/intr/rb-1706.htm">INT 15/AX=DE1Fh</a> - <a href="rb-4122.htm" tppabs="http://www.ctyme.com/intr/rb-4122.htm">INT 28<
<p>
<b>Category: <a href="cat-010.htm" tppabs="http://www.ctyme.com/intr/cat-010.htm">
DOS Kernel</a>
- <a href="int-21.htm" tppabs="http://www.ctyme.com/intr/int-21.htm">
Int 21h</a>
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