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Cache
6-2
Freescale Semiconductor
Instruction and data caches implement line-fill buffers to optimize line-sized burst accesses. The data
cache supports operation of copyback, write-through, or cache-inhibited modes. A four-entry, 32-bit buffer
supports cache line-push operations, and can be configured to defer write buffering in write-through or
cache-inhibited modes. The cache lock feature can be used to guarantee deterministic response for critical
code or data areas.
A non-blocking cache services read or write hits from the processor while a fill (caused by a cache
allocation) is in progress. As
shows, accesses use a single bus connected to the cache.
All addresses from the processor to the cache are physical addresses. A cache hit occurs when an address
matches a cache entry. For a read, the cache supplies data to the processor. For a write, which is permitted
to the data cache only, the processor updates the cache. If an access does not match a cache entry (misses
the cache) or if a write access must be written through to memory, the cache performs a bus cycle on the
internal bus and correspondingly on the external bus.
The cache module does not implement bus snooping; cache coherency with other possible bus masters
must be maintained in software.
6.2
Cache Organization
A four-way set-associative cache is organized as four ways (levels). There are 256 sets in the 16-Kbyte
data cache with each set defined as the grouping of four lines (one from each level, or way), corresponding
to the same index into the cache array. Each line contains 16 bytes (4 longwords). The 16-Kbyte instruction
cache has 256 sets as well. Entire cache lines are loaded from memory by burst-mode accesses that cache
four longwords of data or instructions. All four longwords must be loaded for the cache line to be valid.
shows data cache organization, as well as terminology used.
Figure 6-2. Data Cache Organization and Line Format
Way 0
Way 1
Way 2
Way 3
Line
Set 0
Set 1
•
•
•
•
•
•
•
•
•
•
•
•
TAG
V
M
Longword 0
Longword 1
Longword 2
Longword 3
Where:
TAG—20-bit address tag
V—Valid bit for line
M—Modified bit for line (data cache only)
Cache Line Format
Set 255
Set 254
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...