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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><link rel="STYLESHEET" type="text/css" href="wrs.css"><title> Virtual Memory Interface </title></head><body bgcolor="FFFFFF"><p class="navbar" align="right"><a href="index.html"><img border="0" alt="[Contents]" src="icons/contents.gif"></a><a href="GuideIX.html"><img border="0" alt="[Index]" src="icons/index.gif"></a><a href="c-vm.html"><img border="0" alt="[Top]" src="icons/top.gif"></a><a href="c-vm3.html"><img border="0" alt="[Prev]" src="icons/prev.gif"></a><a href="c-vm5.html"><img border="0" alt="[Next]" src="icons/next.gif"></a></p><font face="Helvetica, sans-serif" class="sans"><h3 class="H2"><i><a name="84463">7.4 General Use</a></i></h3></font><dl class="margin"><dl class="margin"><dd><p class="Body"><a name="84466"> </a>This section describes VxVMI's general use and configuration for write-protecting text segments and the exception vector table.</p><dd><p class="Body"><a name="84468"> </a>VxVMI uses the MMU to prevent portions of memory from being overwritten. This is done by write-protecting pages of memory. Not all target hardware supports write protection; see the architecture appendices in this manual for further information. For most architectures, the page size is 8KB. An attempt to write to a memory location that is write-protected causes a bus error. </p><dd><p class="Body"><a name="84471"> </a>When VxWorks is loaded, all text segments are write-protected; see <a href="c-vm3.html#84391"><i class="title">7.3 Virtual Memory Configuration</i></a>. The text segments of additional object modules loaded using<b class="routine"><i class="routine"> ld</i></b><b>(</b> <b>)</b> are automatically marked as read-only. When object modules are loaded, memory to be write-protected is allocated in page-size increments. No additional steps are required to write-protect application code.</p><dd><p class="Body"><a name="84474"> </a>During system initialization, VxWorks write-protects the exception vector table. The only way to modify the interrupt vector table is to use the routine <b class="routine"><i class="routine">intConnect</i></b><b>(</b> <b>)</b>, which write-enables the exception vector table for the duration of the call. </p><dd><p class="Body"><a name="84475"> </a>To include write-protection, select the following in the project facility VxWorks view:</p><dl class="margin"><dd><div class="Indent"><a name="84476"> </a><b class="symbol_UC">INCLUDE_MMU_FULL <br>INCLUDE_PROTECT_TEXT <br>INCLUDE_PROTECT_VEC_TABLE</b></div><br></dl></dl></dl><a name="foot"><hr></a><p class="navbar" align="right"><a href="index.html"><img border="0" alt="[Contents]" src="icons/contents.gif"></a><a href="GuideIX.html"><img border="0" alt="[Index]" src="icons/index.gif"></a><a href="c-vm.html"><img border="0" alt="[Top]" src="icons/top.gif"></a><a href="c-vm3.html"><img border="0" alt="[Prev]" src="icons/prev.gif"></a><a href="c-vm5.html"><img border="0" alt="[Next]" src="icons/next.gif"></a></p></body></html><!---by WRS Documentation (), Wind River Systems, Inc. conversion tool: Quadralay WebWorks Publisher 4.0.11 template: CSS Template, Jan 1998 - Jefro --->?? 快捷鍵說明
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