在AMBA协议中我们会问WRAP BURST是做什么用的, 答曰是作为CACHE LINE来使用。+ Q3 e% r8 V. j+ x
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那CACHE LINE是什么东西呢？( }4 q1 Z- z) w( J/ c: [
CACHE LINE是在主存和CACHE之间传送的最小单位，当CACHE读取SDRAM时，会同时读取邻近的数据。
& y8 b& ^) y" D; p5 K. w这时BURST就发挥作用，因为SDRAM支持BURST的快速传输。' Y) B3 K/ Z; j: \5 p; F
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那为什么会是WRAP读取的呢？$ E; U' _1 F8 M8 [4 o; W- s
我也不知道，求答案。

IT is The smallest unit of memory than can be transferred between the main memory and the cache.  Rather than reading a single word or byte from main memory at a time, each cache entry is usually holds a certain number of words, known as a "cache line" or "cache block" and a whole line is read and cached at once.  This takes advantage of the principle of locality of reference: if one location is read then nearby locations (particularly following locations) are likely to be read soon afterwards.  It can also take advantage of page-mode DRAM which allows faster access to consecutive locations.

wrap传输是设计用于cache访问内存等情况下的读写的，但它本身的定义并不是针对cache line来定义的，它的传输地址是靠size和burst长度来计算的，到达边界时就wrap回来。