inst_s58.htm

来自「ST20 Embedded Toolset R2.0.5用于开发基于ST20芯片」· HTM 代码 · 共 83 行

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<h2>
  <a name="1102860"> </a><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">smacloop</font>
</h2><hr>


<p>
  <a name="1102866"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">short multiply accumulate loop</font>
</p>


<h5>
  <a name="1105297"> </a><i><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">Code</font></i>
</h5>


<p>
  <a name="1102867"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">21 F6</font>
</p>


<h5>
  <a name="1106083"> </a><i><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">Description</font></i>
</h5>


<p>
  <a name="1102868"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Multiply pairs of signed 16-bit values and accumulate the products. On entry <span class=Signal>Areg</span> and <span class=Signal>Breg</span> contain the addresses of arrays X and Y of 16-bit values and <span class=Signal>Creg</span> holds the initial 32-bit accumulator. On exit the accumulator is in <span class=Signal>Areg</span>, while <span class=Signal>Breg</span> and <span class=Signal>Creg</span> contain the next addresses in the X and Y arrays respectively. The X values can be in a circular buffer whose address is exactly divisible by the size. The loop count, buffer size, mode and scaling codes, held in the <span class=Signal>status</span> register, may be set by the <strong>smacinit</strong> instruction.</font>
</p>


<p>
  <a name="1116128"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif"><em>Note:	 This instruction is not interruptible. If interrupt latency is critical then a similar result may be achieved by executing the instruction many times with small counts. The result may not be the same, since rounding occurs at the end of the instruction from the internal 48-bit accumulator to a 32-bit result.</em></font>
</p>

<h5>
  <a name="1108129"> </a><i><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">Definition</font></i>
</h5>


<p>
  <a name="1102869"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">if (<span class=Signal>Status</span> <sub>overflow</sub>) <br>

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