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| <title>WAIT/FWAIT—Wait </title></head> |
| <body> |
| <h1>WAIT/FWAIT—Wait</h1> |
| <table> |
| <tr> |
| <th>Opcode</th> |
| <th>Instruction</th> |
| <th>Op/En</th> |
| <th>64-Bit Mode</th> |
| <th>Compat/Leg Mode</th> |
| <th>Description</th></tr> |
| <tr> |
| <td>9B</td> |
| <td>WAIT</td> |
| <td>NP</td> |
| <td>Valid</td> |
| <td>Valid</td> |
| <td>Check pending unmasked floating-point exceptions.</td></tr> |
| <tr> |
| <td>9B</td> |
| <td>FWAIT</td> |
| <td>NP</td> |
| <td>Valid</td> |
| <td>Valid</td> |
| <td>Check pending unmasked floating-point exceptions.</td></tr></table> |
| <h3>Instruction Operand Encoding</h3> |
| <table> |
| <tr> |
| <td>Op/En</td> |
| <td>Operand 1</td> |
| <td>Operand 2</td> |
| <td>Operand 3</td> |
| <td>Operand 4</td></tr> |
| <tr> |
| <td>NP</td> |
| <td>NA</td> |
| <td>NA</td> |
| <td>NA</td> |
| <td>NA</td></tr></table> |
| <h2>Description</h2> |
| <p>Causes the processor to check for and handle pending, unmasked, floating-point exceptions before proceeding. (FWAIT is an alternate mnemonic for WAIT.)</p> |
| <p>This instruction is useful for synchronizing exceptions in critical sections of code. Coding a WAIT instruction after a floating-point instruction ensures that any unmasked floating-point exceptions the instruction may raise are handled before the processor can modify the instruction’s results. See the section titled “Floating-Point Exception Synchronization” in Chapter 8 of the <em>Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1</em>, for more information on using the WAIT/FWAIT instruction.</p> |
| <p>This instruction’s operation is the same in non-64-bit modes and 64-bit mode.</p> |
| <h2>Operation</h2> |
| <pre>CheckForPendingUnmaskedFloatingPointExceptions;</pre> |
| <h2>FPU Flags Affected</h2> |
| <p>The C0, C1, C2, and C3 flags are undefined.</p> |
| <h2>Floating-Point Exceptions</h2> |
| <p>None.</p> |
| <h2>Protected Mode Exceptions</h2> |
| <table class="exception-table"> |
| <tr> |
| <td>#NM</td> |
| <td>If CR0.MP[bit 1] = 1 and CR0.TS[bit 3] = 1.</td></tr> |
| <tr> |
| <td>#UD</td> |
| <td>If the LOCK prefix is used.</td></tr></table> |
| <h2>Real-Address Mode Exceptions</h2> |
| <p>Same exceptions as in protected mode.</p> |
| <h2>Virtual-8086 Mode Exceptions</h2> |
| <p>Same exceptions as in protected mode.</p> |
| <h2>Compatibility Mode Exceptions</h2> |
| <p>Same exceptions as in protected mode.</p> |
| <h2>64-Bit Mode Exceptions</h2> |
| <p>Same exceptions as in protected mode.</p></body></html> |