glossary.htm

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<p>
  <a name="1051861"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>stack</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051862"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A stack is a data storage structure that uses a `first in, last out' access model. Adding an item to a stack is called pushing on, and extracting a value is called popping. A program stack is normally implemented using the <span class=Signal>Wptr</span> as the stack pointer. The <span class=Signal>Areg</span>, <span class=Signal>Breg</span> and <span class=Signal>Creg</span> form the <a href="glossary.htm#1051650"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>evaluation stack</i></font></a>.</font>
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<p>
  <a name="1051864"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>stack, evaluation</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051865"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">See <a href="glossary.htm#1051650"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>evaluation stack</i></font></a>.</font>
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<p>
  <a name="1051867"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>state</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051868"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">The state of a process is the data needed for the process to continue execution. This may include the <a href="glossary.htm#1051650"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>evaluation stack</i></font></a>, <a href="glossary.htm#1051728"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>IPTR</i></font></a>, <a href="glossary.htm#1051921"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>WPTR</i></font></a>, <a href="glossary.htm#1051870"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>STATUS register</i></font></a> and <a href="glossary.htm#1051740"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>local</i></font></a> data.</font>
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<p>
  <a name="1051870"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>STATUS register</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051871"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">The <span class=Signal>status</span> register holds CPU status information which must be saved if an <a href="glossary.htm#1051710"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>interrupt</i></font></a> occurs but is not saved if the process deschedules. Some <span class=Signal>status</span> register bits are global and are preserved when a process is descheduled and others are local to a <a href="glossary.htm#1051804"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process</i></font></a> and are lost when the process is <a href="glossary.htm#1054120"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>deschedule</i></font></a>d.</font>
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<p>
  <a name="1051873"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>task</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051874"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A <a href="glossary.htm#1051804"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process</i></font></a>.</font>
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<p>
  <a name="1051876"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>task descriptor</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051877"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">The identifier of a <a href="glossary.htm#1051804"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process</i></font></a>, which is a pointer to the <a href="glossary.htm#1051807"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process descriptor block</i></font></a>. When a process is executing, the <span class=Signal>Tdesc</span> holds the task descriptor of the process.</font>
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<p>
  <a name="1051879"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>TDESC</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051880"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A 32-bit register which holds the <a href="glossary.htm#1051876"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>task descriptor</i></font></a> of the current <a href="glossary.htm#1051804"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process</i></font></a>.</font>
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<p>
  <a name="1051882"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>thread</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051883"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A dynamically generated <a href="glossary.htm#1051804"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process</i></font></a>.</font>
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<p>
  <a name="1051885"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>timeslice</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051886"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">This <a href="glossary.htm#1054120"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>deschedule</i></font></a>s a <a href="glossary.htm#1051804"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process</i></font></a> to allow other processes access to the CPU. Timeslicing prevents any one process from occupying too much CPU time. A timesliced process is normally added to the back of the <a href="glossary.htm#1051834"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>scheduling queue</i></font></a> and the process on the front of the queue is restarted.</font>
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<p>
  <a name="1051888"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>trap</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051889"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">An <a href="glossary.htm#1051653"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>exception</i></font></a> caused by software, or an interrupt initiating a scheduling event.</font>
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<p>
  <a name="1051891"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>trap handler</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051892"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">The code and data which define what happens when a <a href="glossary.htm#1051888"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>trap</i></font></a> is taken.</font>
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<p>
  <a name="1051894"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>trapped</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051895"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A process is trapped when it is waiting for a <a href="glossary.htm#1051891"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>trap handler</i></font></a> to complete.</font>
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<p>
  <a name="1051897"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>unsigned value</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051898"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Value which could only be positive, so the most significant bit is not used as a <a href="glossary.htm#1051849"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>sign bit</i></font></a>.</font>
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<p>
  <a name="1051900"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>vector</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051901"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">An <a href="glossary.htm#1051596"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>array</i></font></a>.</font>
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<p>
  <a name="1051903"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>waiting</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051904"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A <a href="glossary.htm#1051804"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>process</i></font></a> is waiting for an event if it cannot continue execution until that event has occurred. The event could be for example a communication or a <a href="glossary.htm#1051840"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>semaphore</i></font></a> signal.</font>
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<p>
  <a name="1051906"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>word</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051907"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A word is a four byte (32-bit) location for data.</font>
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<p>
  <a name="1051909"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>word-aligned</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051910"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">An <a href="glossary.htm#1051584"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>address</i></font></a> is word-aligned if it is divisible by four, that is, if the least significant two bits are zero.</font>
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<p>
  <a name="1051912"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>work space</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051913"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Space in memory for <a href="glossary.htm#1051740"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>local</i></font></a> variables and values.</font>
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<p>
  <a name="1051915"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>work space cache</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051916"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Registers used to <a href="glossary.htm#1051614"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>cache</i></font></a> the lowest words of the <a href="glossary.htm#1051912"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>work space</i></font></a> in order to accelerate access to local variables. Also called <a href="glossary.htm#1051819"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>register cache</i></font></a> or <a href="glossary.htm#1051822"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>register file</i></font></a>.</font>
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<p>
  <a name="1051918"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>work space pointer</b></font>
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<dl><dl>    <dl>
      <dt> <a name="1051919"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">A 32-bit register pointing to the <a href="glossary.htm#1051912"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>work space</i></font></a> for the <a href="glossary.htm#1051627"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>current process</i></font></a>.</font>
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<p>
  <a name="1051921"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"><b>WPTR</b></font>
<br>

<dl><dl>    <dl>
      <dt> <a name="1051922"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">The <a href="glossary.htm#1051918"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>work space pointer</i></font></a>.</font>
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<p>
  <a name="1051923"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif"></font>
</p>
</blockquote>

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