4-6
MCF5282 User’s Manual
MOTOROLA
Cache Operation
Once an external fetch has been initiated and the data is loaded into the line-fill buffer, the
cache maintains a special “most-recently-used” indicator that tracks the contents of the
associated line-fill buffer versus its corresponding cache location. At the time of the miss,
the hardware indicator is set, marking the line-fill buffer as “most recently used.” If a
subsequent access occurs to the cache location defined by bits [10:4] (or bits [9:4] for split
configurations of the fill buffer address), the data in the cache memory array is now most
recently used, so the hardware indicator is cleared. In all cases, the indicator defines
whether the contents of the line-fill buffer or the memory data array are most recently used.
At the time of the next cache miss, the contents of the line-fill buffer are written into the
memory array if the entire line is present, and the line-fill buffer data is still most recently
used compared to the memory array.
Generally, longword references are used for sequential instruction fetches. If the processor
branches to an odd word address, a word-sized instruction fetch is generated.
For instruction fetches, the fill buffer can also be used as temporary storage for line-sized
bursts of non-cacheable references under control of CACR[CEIB]. With this bit set, a
noncacheable instruction fetch is processed as defined by Table 4-2. For this condition, the
line-fill buffer is loaded and subsequent references can hit in the buffer, but the data is never
loaded into the memory array.
Table 4-2 shows the relationship between CACR bits 31 and 10 and the type of instruction
fetch.
Table 4-2. Instruction Cache Operation as Defined by CACR[31, 10]
CACR[31]
CACR[10]
Type of Instruction Fetch
Description
0
0
N/A
Cache is completely disabled; all instruction fetches are
word or longword in size.
0
1
N/A
All instruction fetches are word or longword in size
1
X
Cacheable
Fetch size is defined by Table 4-1 and contents of the
line-fill buffer can be written into the memory array
1
0
Noncacheable
All instruction fetches are word or longword in size, and
not loaded into the line-fill buffer
1
1
Noncacheable
Instruction fetch size is defined by Table 4-1 and loaded
into the line-fill buffer, but are never written into the
memory array.
Summary of Contents for ColdFire MCF5281
Page 124: ...3 20 MCF5282 User s Manual MOTOROLA EMAC Instruction Set Summary ...
Page 141: ...MOTOROLA Chapter 5 Static RAM SRAM 5 5 SRAM Programming Model ...
Page 142: ...5 6 MCF5282 User s Manual MOTOROLA SRAM Programming Model ...
Page 168: ...6 26 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 186: ...7 18 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 228: ...9 22 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 246: ...10 18 MCF5282 User s Manual MOTOROLA Low Power Wakeup Operation ...
Page 254: ...11 8 MCF5282 User s Manual MOTOROLA Memory Map and Registers ...
Page 264: ...12 10 MCF5282 User s Manual MOTOROLA Chip Select Registers ...
Page 280: ...13 16 MCF5282 User s Manual MOTOROLA Misaligned Operands ...
Page 314: ...14 34 MCF5282 User s Manual MOTOROLA MCF5282 External Signals ...
Page 339: ...MOTOROLA Chapter 15 Synchronous DRAM Controller Module 15 25 SDRAM Example ...
Page 340: ...15 26 MCF5282 User s Manual MOTOROLA SDRAM Example ...
Page 356: ...16 16 MCF5282 User s Manual MOTOROLA DMA Controller Module Functional Description ...
Page 408: ...17 52 MCF5282 User s Manual MOTOROLA Buffer Descriptors ...
Page 446: ...20 24 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 474: ...22 18 MCF5282 User s Manual MOTOROLA Programming Model ...
Page 510: ...23 36 MCF5282 User s Manual MOTOROLA Operation ...
Page 526: ...24 16 MCF5282 User s Manual MOTOROLA I2C Programming Examples ...
Page 672: ...28 12 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 718: ...29 46 MCF5282 User s Manual MOTOROLA Motorola Recommended BDM Pinout ...
Page 750: ...32 8 MCF5282 User s Manual MOTOROLA Ordering Information ...