ARM Technical Support Knowledge Articles

What will happen on a write-miss to a cacheable location?

Applies to: ARM720T

Answer

The cache operates on read-miss replacement only. In the bufferable case, the write will go into the write buffer and the cache will be unaffected. The core continues to execute the next instruction and the write takes place after any previous writes in the write buffer have completed and the ARM720T is granted the AMBA bus.

For an area marked as unbufferable, the cache is again unaffected (as it was a miss). Anything currently in the write buffer will be written out to memory and then the store instruction will complete. (This potentially makes the store operation take quite some time, if the write buffer was full). This means that writes always take place in the same sequence as in the program code.

Note also that any external memory read (such as a cache linefill or access to an uncached location) will always wait for the write buffer to empty, to preserve memory coherency.

Article last edited on: 2008-09-09 15:47:37

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