Compaq ECQD2KCTE Laptop User Manual


 
4–136 Alpha Architecture Handbook
4.11.3 Evict Data Cache Block
Format:
Operation:
va Rbv
IF { va maps to memory space } THEN
Prepare to reuse cache resources that are occupied by the
the addressed byte.
END
Exceptions:
Instruction mnemonics:
Qualifiers:
Description:
The ECB instruction provides a hint that the addressed location will not be referenced again in
the near future, so any cache space it occupies should be made available to cache other mem-
ory locations. If the cache copy of the location is dirty, the processor may start writing it back;
if the cache has multiple sets, the processor may arrange for the set containing the addressed
byte to be the next set allocated.
The ECB instruction does not generate exceptions; if it encounters data address translation
errors (access violation, translation not valid, and so forth) during execution, it is treated as a
NOP.
If the address maps to non-memory-like (I/O) space, ECB is treated as a NOP.
Software Note:
ECB makes a particular cache location available for reuse by evicting and invalidating
its contents. The intent is to give software more control over cache allocation policy in
set-associative caches so that "useful" blocks can be retained in the cache.
ECB is a performance hint — it does not serialize the eviction of the addressed cache
block with any preceding or following memory operation.
ECB (Rb.ab)
! Memory format
None
ECB Evict Cache Block
None