PowerPC e500 Core Family Reference Manual, Rev. 1
11-24
Freescale Semiconductor
L1 Caches
proceed to the CCB. When the instructions are returned, they are forwarded to the instruction unit
but are not loaded into the instruction cache.
The instruction unit fetches a total of four instructions at a time directly from the memory
subsystem for caching-inhibited instruction fetches. Similar to the data cache, when the
instructions are returned, they are forwarded to the instruction unit but are not loaded into any of
the caches in this case.
11.6.1.3 Cache Allocation on Misses
Instruction cache misses cause a new line to be allocated into the instruction cache on a PLRU
basis, provided the cache is not completely locked or disabled.
If there is a data cache miss for a caching-allowed load or store (including touch instructions) and
the line is not already going to be allocated into the data cache as a result of a previous load/store
miss, the miss causes a new line to be allocated into the data cache on a PLRU basis, provided the
cache is not completely locked or disabled. A store that is write-through or caching-inhibited that
misses in the data cache does not cause a fill. Also, cache operations such as dcbi and dcbf that
miss in the cache do not cause a fill.
11.6.1.4 Store Miss Merging
When a caching-allowed store misses in the data cache, an entry is allocated in the DLFB. The
store data is written into the DLFB. The remainder of the bytes not written by the store data are
filled in when the cache block is eventually fetched from memory through the CCB. When all 32
bytes are valid, the cache block is reloaded into the data cache.
If a subsequent store miss hits on a DLFB entry for a previous store miss, the subsequent store
miss also writes its data into the DLFB for that entry. Any number of stores that hit the DLFB entry
created by the original store miss can be written in to the DLFB before it reloads the data into the
data cache. This behavior is known as store miss merging
11.6.1.5 Store Hit to a Data Cache Block Marked Shared
When a write-back store hits in the L1 data cache and the block is in the shared state, the target
block is invalidated in the data cache. The store is then treated as a miss.
11.6.1.6 Data Cache Block Push Operation
When an L1 cache block in the core complex is snooped (by another bus master) and the data hits
and is modified, the cache block must be written to memory and made available to the snooping
device. The push operation propagates to the DWB and then to the CCB.
Содержание PowerPC e500 Core
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