📄 2.2.htm
字号:
<p><span lang=EN-US style='font-size:13.5pt'>
VALID=1 表示TAG字段对应的块号实际上装进了CACHE<br>
<br>
VALID=0 表示TAG 字段对应的块号在CACHE中失效.<br>
</span><span lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'> (4)主存地址格式<br>
TAG CACHE块地址 CACHE块内地址<br>
</span><span lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'> (5)读CACHE操作</span> </p>
<p><span lang=EN-US style='font-size:13.5pt'> 例如:具有8字的CACHE ,固定主存地址的最低3位是块号.下面是每次访问的具体步骤.</span><span
lang=EN-US> <o:p></o:p></span></p>
<div align=center>
<table border=1 cellpadding=0 width="89%" style='width:89.0%;mso-cellspacing:
1.5pt;mso-padding-alt:0cm 0cm 0cm 0cm' bordercolordark="#CC9966"
bordercolorlight="#FFCC66">
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'> </span><span
style='font-size:10.0pt'>十进制访问地址</span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span style='font-size:13.5pt'>二进制访问地址</span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'> 失效或是命中</span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span style='font-size:13.5pt'>分配<span lang=EN-US>CACHE 块</span></span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'> 22 </span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>10110tow
</span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>MISS(7.5B) </span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(10110tow mod
8)=110tow</span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>26 </span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>11010tow</span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'> MISS(7.5C)</span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(11010tow mod
8)=010tow</span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>22</span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>10110tow</span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>HIT </span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(10110tow mod
8)=110tow</span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>26 </span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>11010tow </span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'> HIT </span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(11010tow mod
8)=010tow</span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>16 </span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'> 10000tow </span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>MISS(7.5D) </span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(10000tow mod
8)=000tow</span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>4 </span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>00100tow </span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>MISS(7.5E) </span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(00100tow mod
8)=100tow</span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>16 </span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>10000tow </span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>HIT</span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(10000tow mod
8)=000tow</span></p>
</td>
</tr>
<tr>
<td width="21%" style='width:21.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>18 </span></p>
</td>
<td width="22%" style='width:22.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>10010tow</span></p>
</td>
<td width="18%" style='width:18.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'> MISS(7.5F)</span></p>
</td>
<td width="39%" style='width:39.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:13.5pt'>(10010tow mod 8)=010tow</span></p>
</td>
</tr>
</table>
</div>
<p><span lang=EN-US style='font-size:13.5pt'> 具体步骤是(图7.5)：<br>
<img border=0 width=744 height=272 id="_x0000_i1028"
src="IMAGES\2.2.ht6.gif"><br>
a.初始加电
b.处理10110tow地址后 <img border=0 width=747 height=269 id="_x0000_i1029"
src="IMAGES\2.2.ht7.gif"></span></p>
<p><span lang=EN-US style='font-size:13.5pt'> c.处理11010tow地址失效后 d.处理10000tow地址失后
<img border=0 width=688 height=272 id="_x0000_i1030" src="IMAGES\2.2.ht8.gif"><br>
<br>
e.处理地址00100tow失效后 f.处理地址10010tow失效后</span></p>
<p><span lang=EN-US style='font-size:13.5pt'> (6)调度方法 </span><span
lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'>
当在地址18中的字块被带到CACHE中的2 号位置时,原先在2号位置的地址26 中的数据.这种行为更好的利用了时间局部性—最近要访问的字替换最近最少访问的 字.在直接映射的CACHE
中,只有一个地方来存放所需的元素,因此只有一种替换选择.</span><span lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'>(7)CACHE总容量的计算(BITS)</span><span
lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'> 总容量(BITS)=2<sup>n</sup>*(块大小+TAG大小+有效位)</span><span
lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'> 在MIPS中 <br>
块大小=1字(32位) 地址宽度=1字(32位)</span><span
lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'>
总容量=2<sup>n</sup>*(32+(32-n-2)+1)=2<sup>n</sup>*(63-n) <br>
<br>
例如: 64K字节的数据,CACHE需多少总容量?</span><span
lang=EN-US> </span></p>
<p><span lang=EN-US style='font-size:13.5pt'> 解:
64KB=16K words 即n=14<br>
<br>
2*(63-14)=2*49=784Kbits</span></p>
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