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study/Ref-docs/manual Intel386/I386Manual/CLTS.HTM Normal file
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<html><!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html>
<head>
<title>80386 Programmer's Reference Manual -- Opcode CLTS</title>
</head>
<body>
<b>up:</b> <a href="C17.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C17.HTM">Chapter 17 -- 80386 Instruction Set</a><br>
<b>prev:</b><a href="CLI.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/CLI.HTM"> CLI Clear Interrupt Flag</a><br>
<b>next:</b><a href="CMC.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/CMC.HTM"> CMC Complement Carry Flag</a>
<p>
<hr>
<p>
<h1>CLTS -- Clear Task-Switched Flag in CR0</h1>
<pre>
Opcode Instruction Clocks Description
OF 06 CLTS 5 Clear task-switched flag
</pre>
<h2>Operation</h2>
<pre>
TS Flag in CR0 := 0;
</pre>
<h2>Description</h2>
CLTS clears the task-switched (TS) flag in register CR0. This flag is set by the 80386 every time a task switch occurs. The TS flag is used to manage processor extensions as follows:
<ul>
<li>Every execution of an ESC instruction is trapped if the TS flag is set.
<li>Execution of a WAIT instruction is trapped if the MP flag and the TS flag are both set.
</ul>
Thus, if a task switch was made after an ESC instruction was begun, the processor extension's context may need to be saved before a new ESC instruction can be issued. The fault handler saves the context and resets the TS flag.
<p>CLTS appears in operating system software, not in application programs. It is a privileged instruction that can only be executed at privilege level 0.
<h2>Flags Affected</h2>
TS := 0 (TS is in CR0, not the flag register)
<h2>Protected Mode Exceptions</h2>
#GP(0) if CLTS is executed with a current privilege level other than 0
<h2>Real Address Mode Exceptions</h2>
None (valid in Real Address Mode to allow initialization for Protected Mode)
<h2>Virtual 8086 Mode Exceptions</h2>
Same exceptions as in Real Address Mode
<p>
<hr>
<p><b>up:</b> <a href="C17.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C17.HTM">Chapter 17 -- 80386 Instruction Set</a><br>
<b>prev:</b><a href="CLI.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/CLI.HTM"> CLI Clear Interrupt Flag</a><br>
<b>next:</b><a href="CMC.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/CMC.HTM"> CMC Complement Carry Flag</a>
</body>