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MIPS – Memory Access Types: MIPS system provide several memory access types. These are characteristic ways to use physical memory and caches to perform a memory access.

The memory access type is identified by the Cacheability & Coherency Attribute (CCA) bits in the TLB entry for each mapped virtual page. The access type used for a location is associated with the virtual address, not the physical address or the instruction making the reference.

Memory access type

•  Uncached
• Cached

Uncached Memory Access Type : In an uncached memory access , physical memory resolves the access. Each reference causes a read or write to physical memory. Caches are not examined or modified.

Cached Memory Access Type:  In a cached access physical memory and all caches in the system containing a copy of th ephysical location are used to resolve the accesss. A copy of  a location is coherent if the copy was placed in the cache by a cached coherent access. A xopy of a location is non coherent if the copy ws placed in the cache by a cached non-coherent access. (Coherency is dctated by the system architecture not the processor implementation).

Caches containing a coherent copy of the location are examined and / or modified to keep the content of the location coherent . It is not possible to predict whether caches holding a noncoherent copy of the location will be examined and / or modified during a cached coherent access.

Originally Posted On: 2010-08-29 03:32:49

Anshul Makkar, anshul_makkar@justkernel.com