AVR32AP datasheet(75/181 Pages) ATMEL

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32001A–AVR32–06/06

AVR32

7.2

Write buffer behaviour

Reset invalidates the entire write buffer.

Writes are separated into "write now" (unbufferable) and "write later" (bufferable) writes. Multiple

bufferable writes to the same aligned 32-byte line may be merged for performance, and reads

may forward buffered data directely from the buffer. Bufferable writes will stay in the write buffer

until forced out when one of the following occur:

A buffered write is to another 32-byte line than the one currently in the buffer. The old data are

moved to the "write now" part of the buffer, and the new data are kept as "write later".

A read finds only part of the requested data in the write buffer, e.g a word read finds one byte of

the word in the write buffer. The buffered data are moved to the "write now" part of the buffer,

and the read is qued until the write has completed. This ensures data consistency.

A SYNC instruction is executed. All data in the write buffer are written to the bus.

Unbufferable writes are put in the "write now" part of the buffer. These are written to the bus at

the earliest oportunity, in the same order as issued, and without any write combining. These

data cannot be forwarded by reads, and are always performed before any read misses.

7.3

Cache and write buffer operations

7.3.1

The Cache instruction

The cache instruction can be used to send special commands to the cache with a 32-bit param-

eter. Se the architecture reference manual for description of the instruction. The following

commands are currently defined:

Table 7-1.

Cache instruction parameters

Op[4:3]

Op[2:0]

Operation

Parameter

000

Flush

Flush Mode

001

Lock

Virtual Address

010

Unlock

Virtual Address

011

Invalidate

Virtual Address

100

Clean

Virtual Address

101

Clean & Invalidate

Virtual Address

110

Reserved for future use

Undefined

111

Reserved for future use

Undefined

Other

xxx

Reserved for other caches

N/A

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