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Caches and write buffer
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NS9750 Hardware Reference
The DCache stores the Physical Address Tag (PA tag) corresponding to each
DCache entry in the tag RAM for use during cache line write-backs, in
addition to the virtual address tag stored in the tag RAM. This means that
the MMU is not involved in DCache write-back operations, which removes
the possibility of TLB misses to the write-back address.
Cache maintenance operations provide efficient invalidation of:
– The entire DCache or ICache
– Regions of the DCache or ICache
– Regions of virtual memory
Cache maintenance operations also provide for efficient cleaning and
invalidation of:
– The entire DCache
– Regions of the DCache
– Regions of virtual memory
The latter allows DCache coherency to be efficiently maintained when small
code changes occur; for example, for self-modifying code and changes to
exception vectors.
Write buffer
The write buffer is used for all writes to a noncachable bufferable region, write-
through region, and write misses to a write-back region. A separate buffer is
incorporated in the DCache for holding write-back data for cache line evictions or
cleaning of dirty cache lines.
The main write buffer has a 16-word data buffer and a four-address buffer.
The DCache write-back buffer has eight data word entries and a single
address entry.
The
MCR drain write buffer instruction enables both write buffers to be drained under
software control.
The
MCR wait -for-interrupt causes both write buffers to be drained, and the
ARM926EJ-S processor to be put into low-power state until an interrupt occurs.