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<title>7.2 Descheduled processes</title>
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<a name="1102203"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">7.2 Descheduled processes</font>
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<a name="1102204"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">If the process is waiting for a peripheral or a semaphore or descheduled by a timeslice then the evaluation stack is not saved. The instruction pointer and <span class=Signal>Wptr</span> are saved in the process descriptor block. The task descriptor is the address of the process descriptor block. It therefore identifies the waiting process and points to its saved state. The task descriptor is a fixed address for each process, unlike the <span class=Signal>Wptr</span> which changes as the code executes. When the process is running, the task descriptor is held in the <span class=Signal>Tdesc</span> register. <font face="Verdana, Arial, Helvetica, sans-serif">
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<caption><b><i><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102238"> </a><font face="Helvetica">Table 38: Process descriptor block </font></font></i></b></caption>
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<th><font face="Verdana, Arial, Helvetica, sans-serif" color="#003366"><a name="1102210"> </a><font face="Verdana, Arial, Helvetica, sans-serif">Word offset</font></font></th>
<th><font face="Verdana, Arial, Helvetica, sans-serif" color="#003366"><a name="1102212"> </a><font face="Verdana, Arial, Helvetica, sans-serif">Slot name</font></font></th>
<th><font face="Verdana, Arial, Helvetica, sans-serif" color="#003366"><a name="1102214"> </a><font face="Verdana, Arial, Helvetica, sans-serif">Purpose</font></font></th>
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<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102216"> </a><div ><font size=2>2</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102219"> </a><div ><font size=2><span class=Signal>pw.Iptr</span></font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102221"> </a><div ><font size=2>The process saved instruction pointer.</font></div></font></td>
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<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102223"> </a><div ><font size=2>1</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102225"> </a><div ><font size=2><span class=Signal>pw.Wptr</span></font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102227"> </a><div ><font size=2>The process saved work space pointer.</font></div></font></td>
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<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102229"> </a><div ><font size=2>0</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102232"> </a><div ><font size=2><span class=Signal>pw.Link</span></font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1102234"> </a><div ><font size=2>The link to the next process in the queue.</font></div></font></td>
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<a name="1102246"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The structure of the process descriptor block is shown in <a href="mult_ts3.htm#1102238"><font color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>Table⌨️ 快捷键说明
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