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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
<html>
<head>
<meta http-equiv="Content-Type"
content="text-html; charset=Windows-1252">
<title>INT 21,34 - Get Address to DOS Critical Flag INDOS</title>
<meta name="FORMATTER" content="Microsoft FrontPage 2.0">
</head>
<body>
<h1><a name="kap_interrupt_1940"></a>INT 21,34 - Get Address to
DOS Critical Flag INDOS (Undocumented DOS 2.0+)</h1>
<p> AH = 34h</p>
<p> on return:</p>
<p> ES:BX = address of a byte indicating whether a DOS call is</p>
<p> in progress. No DOS calls should be made if set.</p>
<p> - AKA the INDOS flag, this critical section flag may be
checked from</p>
<p> within an interrupt handler before requesting a DOS service.
It is</p>
<p> a semaphore that is non-zero when DOS is busy, and zero
otherwise.</p>
<p> - though this flag indicates whether a DOS interrupt is
active, it</p>
<p> should not be used alone to determine DOS is safe for
re-entry;</p>
<p> Here's the standard rule for safe DOS entry: if ~INT 28~ is
active</p>
<p> or this flag and the critical error flag are clear then it is
safe</p>
<p> to call DOS</p>
<p> - this interrupt should be used only during TSR
initialization;</p>
<p> the returned pointer should be used thereafter</p>
<p> - this flag is cleared after a critical error (~INT 24~)</p>
<p> - ES:BX-1 points to the critical error flag for DOS 3.x+</p>
<p> ES:BX+1 points to the critical error flag for DOS 2.x</p>
<p> ES:BX-1AA points to the critical error flag for COMPAQ DOS
3.0</p>
<p> ~INT 21,5D~ in DOS 3.x+ can be used to locate the critical</p>
<p> error flag</p>
<hr>
<table border="0" width="100%" cols="3">
<tr>
<td width="33%">Zur<EFBFBD>ck zum <a href="inte1at0.htm">Interrupt
Info</a>. </td>
<td align="center" width="33%"><a
href="mailto:Roger.Morgan@htl-steyr.ac.at">Roger Morgan</a>
/ 1998 </td>
<td align="right" width="33%"><font size="1">L.<2E>nderung <!--webbot
bot="Timestamp" s-type="EDITED" s-format="%d.%m.%y"
startspan -->29.03.99<!--webbot bot="Timestamp" endspan
i-checksum="13964" --> </font></td>
</tr>
</table>
</body>
</html>