AVR32AP datasheet(71/181 Pages) ATMEL

71 / 181 page

32001A–AVR32–06/06

AVR32

6.2.4

The Unlock operation

The unlock operation will try to unlock the line containing the address given by the parameter.

The address is treated as a virtual address, and is translated to a physical address by the MMU.

If the line exists in the cache and is locked, it is unlocked. Otherwise nothing is done. If any MMU

exceptions happen, the operation is silently aborted.

6.2.5

The Prefetch operation

The prefetch operation will try to load the line containing the address given by the parameter into

the cache. The address is treated as a virtual address, and is translated to a physical address by

the MMU. If the line exists in the cache, nothing is done. If the line does not exist in the cache, it

will be fetched from the bus - even if the area is uncacheable. If any exceptions happen - MMU

or bus exceptions - the operation is silently aborted.

6.3

Memory coherency

Whenever code is modified in some way, e.g. through self-modifying code, there is a chance

that the instruction cache may hold cached copies of the old instructions. To ensure correct exe-

cution of the new code, the user must manually force the caches to update. The procedures for

doing so are described below.

6.3.1

DMA of program code

If some peripheral updates program code through DMA to memory, the instruction cache may

hold cached copies of the old code. The old code must be manually flushed from the instruction

cache by following these steps:

Flush the entire instruction cache, as described in chapter 6.2.1, or

Flush only the affected memory areas through one or more Invalidate operations, as

described in chapter 6.2.2.

Jump to the new code using an unpredicted branch

Example:

mov R0, 0

cache ICACHE_FLUSH, R0[ICACHE_INVALIDATE_ALL]

mov PC, new_code_label

6.3.2

Self-modifying code

If the CPU updates the code through writing to memory, the updated code may be buffered in

the data cache or the write buffer, and the instruction cache may hold cached copies of the old

code. The caches must be manually updated by following these steps:

Clean the entire data cache, as described in TODO, or

Clean only the affected memory areas through one or more Clean operations, as

described in TODO.

Empty the write buffer, as described in TODO

Flush the entire instruction cache, as described in chapter 6.2.1, or

Flush only the affected memory areas through one or more Invalidate operations, as

described in chapter 6.2.2.

Jump to the new code using an unpredicted branch

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