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Cache
Freescale Semiconductor
6-15
Figure 6-7. Write-Miss in Copyback Mode
The new cache line is then updated with write data and the M bit is set for the line, leaving it in modified
state. Write misses to write-through regions write directly to memory without loading the corresponding
cache line into the cache.
6.4.2.3
Read Hit
On a read hit, the cache provides the data to the processor core and the cache line state remains unchanged.
If the cache mode changes for a specific region of address space, lines in the cache corresponding to that
region that contain modified data are not pushed out to memory when a read hit occurs within that line.
First, execute a CPUSHL instruction or set CACR[DCINVA,ICINVA] before switching the cache mode.
6.4.2.4
Write Hit (Data Cache Only)
The cache controller handles processor writes that hit in the data cache differently for write-through and
copyback regions. For write hits to a write-through region, portions of cache lines corresponding to the
size of the access are updated with the data. The data is also written to external memory. The cache line
state is unchanged. For copyback accesses, the cache controller updates the cache line and sets the M bit
for the line. An external write is not performed and the cache line state changes to (or remains in) the
modified state.
Cache Line
System
V = 1
M = 0
1. Writing character X to 0x0B generates a write miss. Data cannot be written to an invalid line.
Memory
V = 0
M = 0
0x0C
0x00
0x08
0x04
2. The cache line (characters A–P) is updated from system memory, and the line is marked valid.
X
ABCD EFGH IJKL MNOP
3. After the cache line is filled, the write that initiated the write miss (the character X) completes to 0x0B.
V = 1
M = 1
0x0C
0x00
0x08
0x04
0x0C
0x00
0x08
0x04
ABCD EXGH IJKL MNOP
ColdFire
processor
ColdFire
processor
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 ...