ARM.SoC.Architecture

The same one cycle penalty applies to branch and link

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Unformatted text preview: The I-cache holds 16 Kbytes of instructions in 512 lines of eight instructions (32 bytes). The cache is 32-way associative (using a CAM-RAM organization) with a cyclic replacement algorithm and uses the processor's virtual address. The block size is the same as the line size, so whole lines are loaded from memory at a time. Individual areas of memory may be marked as cacheable or uncacheable using the memory management tables, and the cache may be disabled and flushed (in its entirety) under software control. The data cache uses a similar organization to the instruction cache but with added functions to cope with data stores (instructions are read-only). It has a capacity of 16 Kbytes with 512 32-byte lines arranged as a 32-way virtually addressed associative cache with cyclic replacement. The block size is also 32 bytes. The cache may be disabled by software and individual regions of memory may be made uncacheable. (Making I/O regions uncacheable is usually a good idea.) The data cache uses a copy-back write strategy, and has two dirty bits per line so that when a line is evicted from the cache all, half or none of it is written to memory. The use of two dirty bits rather than one reduces memory traffic since the 'half dirty' case is quite common. The cache stores a copy of the physical address with each line for use when the line is written back to memory, and evicted lines are placed into the write buffer. Since the cache uses a copy-back write strategy, it is sometimes necessary to cause all dirty lines to be written back to memory. On StrongARM this is achieved using software to load new data into every line, causing dirty lines to be evicted. As with any virtually addressed cache, care must be taken to ensure that all cacheable physical memory locations have unique virtual addresses that map to them. When two different virtual addresses map to the same physical location the virtual addresses are synonyms; where synonyms exist, neither virtual address should be cacheable. Multiplier Instruction cache Data cache Synonyms The StrongARM SA-110 333 Cache consistency The separate instruction and data cach...
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